Dissertations / Theses on the topic 'Brachytherapy'

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2008.
Includes bibliographical references (p. 131-139).
The practice of brachytherapy and brachytherapy dosimetry was investigated with emphasis on evaluations of dose distributions and shielding considerations for both photon- and neutron-emitting radionuclides. Monte Carlo simulation methods were employed to calculate dose distributions for virtual and commercial brachytherapy sources. Radionuclides studied were 103Pd, 1251, 131Cs, 137Cs, 169b, 192Ir, and 252Cf. 252Cf sources also emit neutrons from spontaneous fission. The brachytherapy dosimetry protocol recommended by the American Association of Physicists in Medicine was followed and evaluated for conditions of partial scatter (non-infinite media) and material inhomogeneities, both commonly encountered in brachytherapy treatment. Furthermore, energy-dependent characteristics of dosimetry parameters were evaluated and reference calculations performed for virtual photon and neutron sources. These findings were applied to three clinical brachytherapy cases: eye plaques using 103Pd, 125I, and 131Cs; high-dose rate 252Cf treatment; and, 2 Cf plaques for superficial lesions. For eye plaques, material heterogeneities were significant for each radionuclide with dose reduction at 5 mm of 18%, 11%, and 10% for P03pd, 125I, and 131Cs, respectively. For a proposed highdose rate 252Cf source (5mm length), relative brachytherapy dosimetry parameters were found to be similar to those obtained for a low-dose rate Applicator Tube-type source (15 mm length). Considering 252Cf plaque brachytherapy when partial scatter conditions were accounted for, central axis equivalent dose rate decreased by 11 ± 1% and 7 ± 2% for depths of 4 to 50 mm, respectively.
(cont.) The ratio of neutron dose to total physical dose was 70 ± 1% and 57 ± 2% for depths of 4 and 50 mm, respectively, while the fractional dose-equivalent due to neutrons was 93 + 1% and 89 ± 2% at these depths, respectively. Finally, shielding requirements for a clinical high-dose rate 252Cf source were explored for common shielding materials and a linear accelerator vault. Lead, polyethylene, and borated polyethylene were evaluated for neutron, primary photon, and secondary photon attenuation. Half-value layers of 0.70, 0.15, and 0.13 m were obtained for lead, polyethylene, and borated polyethylene, respectively. A linear accelerator vault was found to adequately shield up to a 5 mg 252Cf source for regular clinical use.
by Christopher S. Melhus.
Ph.D.

Photoacoustic (PA) imaging is an emerging imaging modality that relies on the PA effect. The PA effect is caused by exposing an optically absorbing sample to near-infrared light which causes the sample to experience a temporary temperature increase through optical absorption. The heated region undergoes thermoelastic expansion and produces an abrupt and localized pressure change. This change results in a transient PA wave that propagates out toward the sample surface for collection by an ultrasound (US) transducer. Through image reconstruction, the optical property of the sample can be obtained. PA imaging is promising in detecting brachytherapy seeds during prostate brachytherapy. The high absorption coefficient of the metallic seeds leads to high PA imaging contrast. One major drawback is the limited imaging depth due to high optical attenuation of the excitation light in tissue. One of the goals of this thesis is to conduct initial feasibility tests of enhancing the PA contrast through brachytherapy seeds modifications. Seed coated with a contrast enhancing material shows an increase of 18 dB in signal-to-noise ratio (SNR) and two time increase in the imaging depth (5 cm). Another method of silver coating leads to a 5 dB improvement in the SNR of the modified seeds. An alternative approach in using dyed ethanol solution as a contrast enhancing agent by filling the spaces between two seeds is also reported. The result showed improvement comparable to the black paint method. Another goal is to propose a novel method of tissue typing in PA imaging. A temperature change in tissue can lead to changes of several tissue parameters which can be used for tissue typing. One of the parameters is the speed of sound in tissue, which increases in water-based non-fatty tissue and decreases in fatty tissue as temperature is raised. We show that on average, 6.9±1.5 %/min increase and 4.2±1.5 %/min decrease in PA intensity are observed in porcine liver and bovine fat samples respectively through one minute of laser heating. These results demonstrate that by analyzing the PA intensity change of the illuminated sample, one can extract characteristic information that can lead to tissue type differentiation.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

One out of eight deaths throughout the world is due to cancer. Developing new treatments and improving existing treatments is hence of major importance. In this thesis we have studied how mathematical optimization can be used to improve an existing treatment method: high-dose-rate (HDR) brachytherapy. HDR brachytherapy is a radiation modality used to treat tumours of for example the cervix, prostate, breasts, and skin. In HDR brachytherapy catheters are implanted into or close to the tumour volume. A radioactive source is moved through the catheters, and by adjusting where the catheters are placed, called catheter positioning, and how the source is moved through the catheters, called the dwelling time pattern, the dose distribution can be controlled. By constructing an individualized catheter positioning and dwelling time pattern, called dose plan, based on each patient's anatomy, it is possible to improve the treatment result. Mathematical optimization has during the last decade been used to aid in creating individualized dose plans. The dominating optimization model for this purpose is a linear penalty model. This model only considers the dwelling time pattern within already implanted catheters, and minimizes a weighted deviation from dose intervals prescribed by a physician. In this thesis we show that the distribution of the basic variables in the linear penalty model implies that only dwelling time patterns that have certain characteristics can be optimal. These characteristics cause troublesome inhomogeneities in the plans, and although various measures for mitigating these are already available, it is of fundamental interest to understand their cause. We have also shown that the relationship between the objective function of the linear penalty model and the measures commonly used for evaluating the quality of the dose distribution is weak. This implies that even if the model is solved to optimality there is no guarantee that the generated plan is optimal with respect to clinically relevant objectives, or even near-optimal. We have therefore constructed a new model for optimizing the dwelling time pattern. This model approximates the quality measures by the concept conditional value-at-risk, and we show that the relationship between our new model and the quality measures is strong. Furthermore, the new model generates dwelling time patterns that yield high-quality dose distributions. Combining optimization of the dwelling time pattern with optimization of the catheter positioning yields a problem for which it is rarely possible to find a proven optimal solution within a reasonable time frame. We have therefore developed a variable neighbourhood search heuristic that outperforms a state-of-the-art optimization software (CPLEX). We have also developed a tailored branch-and-bound algorithm that is better at improving the dual bound than a general branch-and-bound algorithm. This is a step towards the development of a method that can find proven optimal solutions to the combined problem within a reasonable time frame.

Low-dose-rate prostate brachytherapy is a minimally invasive treatment approach for localized prostate cancer. It takes place in one session by permanent implantation of several small radio-active seeds inside and adjacent to the prostate. The current procedure at the majority of institutions requires planning of seed locations prior to implantation from transrectal ultrasound (TRUS) images acquired weeks in advance. The planning is based on a set of contours representing the clinical target volume (CTV). Seeds are manually placed with respect to a planning target volume (PTV), which is an anisotropic dilation of the CTV, followed by dosimetry analysis. The main objective of the plan is to meet clinical guidelines in terms of recommended dosimetry by covering the entire PTV with the placement of seeds. The current planning process is manual, hence highly subjective, and can potentially contribute to the rate and type of treatment related morbidity. The goal of this thesis is to reduce subjectivity in prostate brachytherapy planning. To this end, we developed and evaluated several frameworks to automate various components of the current prostate brachytherapy planning process. This involved development of techniques with which target volume labels can be automatically delineated from TRUS images. A seed arrangement planning approach was developed by distributing seeds with respect to priors and optimizing the arrangement according to the clinical guidelines. The design of the proposed frameworks involved the introduction and assessment of data fusion techniques that aim to extract joint information in retrospective clinical plans, containing the TRUS volume, the CTV, the PTV and the seed arrangement. We evaluated the proposed techniques using data obtained in a cohort of 590 brachytherapy treatment cases from the Vancouver Cancer Centre, and compare the automation results with the clinical gold-standards and previously delivered plans. Our results demonstrate that data fusion techniques have the potential to enable automatic planning of prostate brachytherapy.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

The Axxent device developed by Xoft Inc. is a novel electronic brachytherapy system capable of generating x-rays up to 50 keV. The objective of this study is to characterize the x-ray beam and to model the x-ray tube using the Geant4 Monte Carlo code. Spectral measurements are done using an Amptek XR-100T CdTe spectrometer. Attenuation curves are measured using both a NE-2571 farmer chamber and a PTW-23342 parallel plate chamber. 2-D dose distributions are measured using EBT Gafchromic films. The Geant4 Monte Carlo code is bench-marked against BEAMnrc results. HVL values and effective energies are obtained from spectral measurements, attenuation curve measurements, and Geant4 simulations. The results mostly agree within one standard deviation. Measurements show that the HVL decreases with beam angle. However, this trend is not observed in Geant4 results. 2-D dose distributions are compared with Geant4 Monte Carlo results. The agreement is mostly within 10 %. However, there are significant differences aft of the source.
La sonde Axxent, conçu par Xoft inc., est un nouveau système de curiethérapie électronique qui peut générer des rayons X avec une énergie maximum de 50 keV. L'objectif de cette étude est de décrire le spectre de rayons X émis et de créer un modèle du tube à rayons X en utilisant le code de Monte Carlo Geant4. Les mesures de spectres ont été réalisées à l'aide d'un spectromètre CdTe XR-100T de marque Amptek. Les courbes d'atténuation ont été mesurées à l'aide de deux chambres d'ionisation: une chambre NE-2571 de type Farmer et une chambre PTW-23342 de type chambre plate. Des films Garchromiques EBT ont été utilisés pour la mesure de distributions de dose en 2 dimensions autour de la source. Les résultats obtenus avec le code Geant4 one été comparés avec les résultats générés grâce à un code de Monte Carlo différent: BEAMnrc. Les épaisseurs de demi-atténuation et les énergies effectives on été également déduites des mesures spectrales, des courbes d'atténuation et des simulations de Geant4. Les résultats s'accordent avec une différence de moins d'un écart-type dans la plupart des cas. Les mesures indiquent que les épaisseurs de demi-atténuation diminuent avec l'angle du rayon choisi pour la mesure. Par contre, cette tendance n'est pas observée dans les simulations Monte Carlo avec Geant4. La comparaison entre les mesures et les calculs de Geant4 des distributions de dose en deux dimensions montre un accord généralement meilleur que 10 %. Néanmoins, il y a des différences importantes en arriére de la source.

Thesis (Ph. D.)--University of Florida, 2001.
Title from first page of PDF file. Document formatted into pages; contains xiii, 140 p.; also contains graphics. Vita. Includes bibliographical references (p. 132-139).

Für die Therapie maligner intranasaler Neoplasien beim Hund existieren nur mäßig be-friedigende Behandlungsstrategien. Als Therapiemodalität der Wahl wird die Radiothe-rapie angesehen, die gegenwärtig v.a. in Form einer perkutanen Bestrahlung (Telethe-rapie) mit aufwendigen, bis zu 20 Fraktionen umfassenden Protokollen kurativer Intenti-on angewendet wird. Die erreichbaren Überlebenszeiten sind meist limitiert durch das Auftreten eines Rezidivs des Nasentumors innerhalb des Bestrahlungsfeldes, sodass eine Erhöhung der applizierten Gesamtdosis nötig erscheint. Dies ist jedoch im Rahmen einer Teletherapie aufgrund nicht vertretbarer akuter Nebenwirkungen nicht möglich. Alternativ steht die Brachytherapie zur Verfügung, die aufgrund ihrer physikalischen Charakteristika zur besseren Schonung des umliegenden Normalgewebes beiträgt. Ge-genwärtig existieren keine anderen Untersuchungen zur Anwendung der fraktionierten High-Dose-Rate-Brachytherapie bei Nasentumoren des Hundes. Ziel dieser Studie war es daher, die Durchführbarkeit dieser Therapiemodalität beim Hund erstmals zu unter-suchen und die akuten und chronischen Nebenwirkungen sowie die erzielbare progres-sionsfreie Zeit und die Überlebenszeit zu dokumentieren. Im Zeitraum von 2001 bis 2007 gingen 18 Hunde in die Studie ein. Das diagnostische Vorgehen beinhaltete neben einer klinischen Untersuchung und der Röntgenuntersu-chung von Nase und Thorax auch die kernspintomographische Beurteilung der Nasen-höhlen und eine nachfolgende Rhinoskopie inklusive Biopsie. Die Therapie bestand aus zwei wöchentlichen Fraktionen, bei denen in Vollnarkose über einen in der Nasenhöhle applizierten Katheter mithilfe des Radioisotops 192Iridium jeweils 5 Gy appliziert wurden. Die damit über vier Wochen erreichte Gesamtdosis lag bei 40 Gy, und entsprach damit der biologischen Effizienz einer perkutan applizierten konventionell fraktionierten Ge-samtdosis von circa 60 Gy. Im Anschluss an die Therapie wurden die Hunde monatlich klinisch untersucht und die auftretenden Nebenwirkungen anhand des Radiation Morbi-dity Scores der VRTOG beschrieben. Es wurden außerdem weiterführende Untersu-chungen in Form von MRT, Rhinoskopie und Biopsie durchgeführt. Die aufgetretenen Nebenwirkungen waren mit denen in der Literatur nach Teletherapie beschriebenen vergleichbar, beziehungsweise fielen im Bereich von Augen und Maulschleimhaut ge-ringer aus. Nebenwirkungen im Bereich der Haut traten in Form von Alopezie, Hyper-pigmentation oder Leukotrichie auf. Im Bereich der Nasenschleimhaut zeigten fast alle Hunde eine leichte chronische Rhinitis. Als problematische Nebenwirkungen traten bei drei Patienten Osteoradionekrosen auf, die einer aufwendigeren chirurgischen Versor-gung bedurften. Die mediane progressionsfreie Zeit lag bei 13 Monaten, die mediane Überlebenszeit bei 17 Monaten. Die Adenokarzinome wiesen die längste Überlebens-zeit auf, dies war jedoch aufgrund der insgesamt kleinen Patientenzahl nicht signifikant. Ein Zusammenhang zwischen dem Tumorstadium und der progessionsfreien Zeit oder Überlebenszeit bestand nicht. Bei dem beschriebenen Protokoll handelt es sich um eine unter klinischen Bedingungen praktikable Therapieform, die mit ihren insgesamt acht Fraktionen für Besitzer und Tier wesentlich weniger belastend ist als teletherapeutische kurative Protokolle mit 12-20 Fraktionen. Gleichzeitig gelingt es, eine Gesamtdosis von verhältnismäßig hoher biolo-gischer Effizienz zu applizieren, ohne jedoch stärkere Nebenwirkungen in Kauf nehmen zu müssen. Im Bereich von Auge und Maulschleimhaut sind die Nebenwirkungen sogar geringer. Bei einem kleinen Teil der Patienten treten jedoch auch hier, ebenso wie nach teletherapeutischen Protokollen, problematische chronische Nebenwirkungen auf, die die Lebensqualität der betroffenen Tiere beeinträchtigen und die einer aufwendigeren Therapie zwingend bedürfen. Die mit diesem Protokoll erreichten Remissions- und Ü-berlebenszeiten sind mit denen aus der Literatur vergleichbar bis tendenziell besser. Aufgrund der oben genannten Vorteile erscheint die vorgestellte Therapie daher als Al-ternative zu Teletherapie bei der Behandlung kaniner Nasentumoren durchaus geeig-net. Weitere Studien mit größeren Patientenzahlen unter Einbeziehung einer anders therapierten Kontrollgruppe sind jedoch notwendig

Radioactive seed implant brachytherapy is a common radiotherapy treatment method for prostate cancer. In current clinical practice, a seed consists of a single isotope, such as 125I or 103Pd. A seed containing a mixture of two isotopes has been proposed for prostate cancer treatment. This study investigates a method for defining a prescription dose for new seed compositions based on matching the biological equivalent dose (BED) of a reference plan. Ten prostate cancer cases previously treated using single isotope seeds (5 using 125I seeds and 5 using 103Pd seeds) were selected for this study. Verification of the method was done by calculating prescription doses for 103Pd and 125I seeds. A prescription dose for a 50/50 hybrid seed was calculated. Number and location of seeds remained invariant within each case. The BED distributions for hybrid and single isotope seed plans were generated and matched to the BED distribution generated off of the optimized plans. For the 125I isotopes, the dose necessary to cover 90% of the prostate with a BED of 110 Gy is 145 Gy. For the same BED coverage, the dose for 103Pd and 50/50 hybrid seed is 120 Gy and 137 Gy respectively. A method is introduced for obtaining prescription doses for new brachytherapy sources. The method was verified by obtaining doses for 125I and 103Pd isotopes which match clinical prescription doses. The method developed is robust enough to calculate prescription doses in any region of interest, for any seed type, and for any isotope as long as the BED coverage remains invariant with respect to the treatment plan. Numerical calculations were performed to derive analytical conversions of total dose to BED for 50/50, 75/25 and 25/75 hybrid seeds. These analytical conversions are faster than the original numerical methods employed allowing for real-time BED optimization for hybrid seeds. Varying seed distribution was seen not to influence the analytical conversions. It was observed that when total dose remained invariant while individual isotope contributions varied, the value of BED varied. The BED variance was seen to be the smaller at larger BED values (~2% at 100 Gy). Using the conversions derived in this paper, BED based optimization for hybrid seeds are now performable. However, these conversions should only be used in high dose regions due to high uncertainty in the low regime.

Magnetic Resonance Imaging (MRI) and Fricke-gelatin dosimetry are used to measure absorbed dose distributions from high dose rate (HDR) brachytherapy treatments. The high activity of the HDR brachytherapy source is suitable for the prompt delivery of the high doses required to give changes in the Fricke-gelatin Nuclear Magnetic Resonance (NMR) characteristics which are readily detected by MRI. The MR images can map 3D dose distributions deposited in the Fricke-gelatin matrix. Spin-lattice relaxation times (T1) and rates (R1) are computed from MR images of irradiated Fricke gelatin phantoms in order to study the dose response relationship for the Fricke gelatin system. It was confirmed that the Fricke gelatin system's R1 varies linearly with absorbed dose to a saturation limit. A fast approach for determining radiation dose from MR image intensity using a calibration curve is described. Dose distributions generated from MR images via the calibration curve show good agreement with expected distributions generated from a computerized treatment plan. As well, dose data generated using R1 maps agreed well with those generated by calibration curve. The use of MRI with Fricke-gel dosimetry is shown to be a viable means of verifying the dose distributions from high activity brachytherapy sources.

In the various brachytherapy techniques the intent is to deliver as high a tumour dose as possible, limited only by surrounding normal tissue tolerance. The main feature of the techniques is very steep dose gradients, representing a potential limiting factor in accurate dose distribution measurements around sources. Dose distributions at distances less than 1 cm are therefore normally generated using either validated Monte Carlo (MC) simulations or standard dose calculation formalisms, for example that of AAPM TG 43, while dose measurements can only be performed at larger distances, normally greater than 1 cm from the outer dimensions of the source encapsulation Ge-doped silica fibres are a viable thermoluminescent dosimetry (TLD) system, providing good spatial resolution of approximately 120 urn, sensitive response to ionizing radiations, large dynamic dose range, good reproducibility and reusability, dose rate independence, minimal fading, resistance to water and low cost. Dosimetric characterisation of commercial Ge-doped silica fibres have been obtained by subjecting them to kilovoltage therapeutic x-ray radiation beams, verifying their use for brachytherapy sources; dose response, reproducibility and fading at 90 kVp and 300 kVp have been investigated. Central-axis depth doses have been obtained at the two accelerating potentials using different field size applicators, measurements being made using the fibres in both water and a GAMMEX RMr 4571 solid water phantom. Comparison has been made with central-axis depth doses, measured using a 0.6 cm3 graphite-walled ionisation chamber data and British Journal of Radiology Supplement 25 tabulated values (both in water). Ge-doped optical fibre dosimeters show good dosimetric response for low photon energies. These desirable characteristics support the use of these TL fibres as dosimeters for brachytherapy applications. Ge-doped optical fibre TL dosimeters have been used to measure the dose distribution around two Low Dose Rate (LDR) 125r seeds; model 6711, the new thinner model 9011 and a High Dose Rate (HDR) 192rr (MicroSelectron V2) source at proximal distances down to 1 mm, measured in a Perspex medium. The anisotropy has also been measured in Perspex, for distances from 10 to 100 mm from a LDR 1251 seed model 6711 centre, in 10 mm increments and at angles 10° to 90° in 10° increments from the seed central axis. Measured doses have been compared with calculations and treatment planning system (TPS) predicted doses for the same locations. Monte Carlo simulations were obtained using the EGSnrc \ DOSRZnrc codes and TPS predicted doses were obtained using the system VariSeed V8.0.2. For 1251 seed model 6711, the measurements agree with simulations to within 2.3 % ± 0.3 % along the transverse and perpendicular axes and within 3.0 % ± 0.5 % for measurements investigating anisotropy in angular dose distribution. Measured and Veriseed™ brachytherapy treatment planning system (TPS) values agreed to within 2.7 % ± 0.5 %. For the new thinner 1251 model 9011, dose measurements were in good agreement with simulations to within 2.1 ± 0.2 %, while dose measurements and doses obtained through use of the Variseed TPS agreed well, to within 2.2 ± 0.5 %. The above work has therefore demonstrated the applicability of Ge-doped optical fibres for use in brachytherapy.

Purpose: To assess rotating shield brachytherapy (RSBT) delivered with the electronic brachytherapy (eBT) source comparing to intracavitary (IC) and intracavitary plus supplemental interstitial brachytherapy (IC+IS BT) delivered with a conventional 192Ir radioactive source. Method and Materials: IC, IC+IS and RSBT treamtent plan were simulated for 5 patients with bulky (>40 cc) cervical cancer. One BT plan for each patient (fraction 1) guided by magnetic resonance imaging (MRI) was used in our treatment planning system (TPS). A bio- and MRI-compatible polycarbonate (Makrolon Rx3158) intrauterine applicator was simulated for IC and RSBT, and the Vienna applicator was simulated for IC+IS BT. 192Ir was used as the radiation source of IC and IC+IS BT, and the Xoft AxxentTM eBT source was used for RSBT. A 0.5 mm thick tungsten shield was used for RSBT with different azimuthal and zenith angles, which reduced radiation transmission through the shield to less than 0.1%. The total dose delivered was calculated as the external beam radiation therapy (EBRT) dose plus the BT dose delivered over five treatment fractions. Results: RSBT and IC+IS BT had higher dose conformity in terms of the minimum dose to the hottest 90% (D90) of the high-risk clinical target volume (HR-CTV) than IC BT for all the patients. The advantage of RSBT over IC+IS BT was dependent on the shield emission angle, tumor shape and tandem applicator location. The delivery time of RSBT was increased as finer emission angle were selected. Conclusions: RSBT is a less-invasive potential alternative to conventional IC and IC+IS BT for treating bulky cervical cancer. RSBT delivery times are clinically acceptable if proper emission angle is selected based on the tumor shape and tandem applicator location.

In this thesis, we aim to develop fundamentally new techniques and algorithms for efficiently computing rotating-shield brachytherapy (RSBT) treatment plans. We propose that these algorithms will pave the way for making RSBT available in clinical practices. RSBT is an intensity modulated high-dose-rate brachytherapy (HDR-BT) technique. Theoretically, RSBT offers advantages over the conventional HDR-BT. Although this technique is promising in theory, its application in practice is still at an early stage. The RSBT technique entails rotating a radiation-attenuating shield about a brachytherapy source to directionally modulate the radiation in an optimized fashion. The unshielded brachytherapy source used in conventional HDR-BT delivers radially symmetric dose distributions, thus the intensity modulation capability of the conventional HDR-BT is limited. With the capability of making anisotropic radiation, RSBT will revolutionize the brachytherapy technique through superior dose conformity, increased flexibility and inherent accuracy. Due to the enhanced power of intensity-modulation, RSBT will also enable dose escalation without increasing toxicity to the organs-at-risk, thus improving quality of life for millions of cancer patients. Although the first conceptual RSBT method was proposed more than ten years ago, there are still tremendous challenges for applying it in clinical practices. Creating efficient and automated treatment planning system is one of the major technical obstacles for making RSBT deliverable in the clinic. The time-critical nature of the application significantly increases the difficulty of RSBT treatment planning, demanding innovative techniques for information integration. Therefore, we propose that fundamentally novel technology and algorithms for RSBT treatment planning can make RSBT clinically accessible. The fundamental concept used for this thesis is to decompose the dose optimization step for RSBT treatment planning into two steps, namely anchor plan optimization and optimal sequencing. The degree of freedom in anchor plan optimization is controlled at a low level compared to single-step dose optimization, and the optimal sequencing algorithms can efficiently calculate treatment plans by reusing the solutions from anchor plan optimization. Thus, by decomposing the dose optimization, the computational complexity in the two-step method is greatly reduced compared to the single-step method. In the anchor plan optimization, an abstract RSBT delivery model is assumed. The abstract RSBT delivery model assumes that only beams with fixed small azimuthal emission angle, which are called beamlets, will be used during the delivery. An anchor plan is created based on this assumption that only these beamlets will be used. Generally, an anchor plan will be of high quality in the sense of dose distribution, but of low quality in the sense that it has prohibitory long delivery time. In the optimal sequencing step, beamlets will be superposed into beams to reduce the delivery time. By limiting the delivery time to a clinically acceptable level, the anchor plans turn into deliverable plans. Unlike anchor plan optimization, where an abstract RSBT delivery model is assumed, the optimal sequencing step depends on more concrete RSBT delivery models. Specifically, we will study three methods of RSBT, namely the single rotating-shield brachytherapy (S-RSBT), the dynamic rotating-shield brachytherapy (D-RSBT) and the paddle rotating-shield brachytherapy (P-RSBT). We proposed a novel anchor plan dose optimization method as well as novel optimal sequencing methods for each of the RSBT delivery methods studied in this work. We have implemented all the proposed algorithms and experimented with them using real medical data. With the methods proposed in this thesis, the optimization time for creating delivery plans can be controlled within 15 minutes based on the data from our experiments. Compared to the conventional brachytherapy techniques, the three methods studied in this work can produce more conformal dose distributions at an acceptable level of delivery time increase. With 15 min/fx delivery time, S-RSBT, D-RSBT and P-RSBT averagely increased the D90 (the minimum dose received by the hottest 90% of the tumor) by 17, 9 and 5 Gy compared to conventional interstitial plus intracavitary brachytherapy, whose D90 is 79 Gy. The best choice depends on the specified delivery time or quality requirement, as well as the complexity of building the equipment. Roughly speaking, among the three RSBT methods studied in this thesis, P-RSBT has the most complex applicators as well as the highest plan qualities. S-RSBT has the simplest applicators, and its plan qualities is generally better than D-RSBT with limited delivery time (/fx). With sufficient delivery time (~30 min/fx), D-RSBT may be considered as the best solution in the sense of balancing the complexity of applicators and the dose qualities.

Multi-helix rotating shield brachytherapy (RSBT) applicator and multi-source RSBT apparatus are two novel intensity-modulated brachytherapy techniques for the treatment of cervical and prostate cancer, respectively. The use of imaging techniques such as magnetic resonance imaging guided brachytherapy has enabled the precise identification and contouring of tumor volumes for treatment planning, as well as demonstrated the challenges associated with using conventional high dose rate brachytherapy (HDR-BT) approaches to conform the radiation dose to the target and avoid surrounding sensitive healthy tissues. The target conformity of conventional HDR-BT dose distributions is restricted based on the geometrical constraints imposed by the position and shape of the tube-shaped applicators, as well as the radially-symmetric radiation dose distributions produced by the radiation sources. Dose distribution conformity for cervical and prostate cancer can be significantly improved relative to conventional HDR-BT through the use of multi-helix and multi-source RSBT techniques, respectively. In this study, two novel RSBT concepts for treating cervical and prostate cancer were introduced and the dosimetric impact was evaluated. A Henschke-type cervical cancer applicator, designed for an electronic brachytherapy (eBx) source (Xoft AxxentTM) and a 0.5 mm thick tungsten partial shield with 180° or 45° azimuthal emission angles, is proposed. The interior wall of the applicator contains six evenly-spaced helical keyways that rigidly define the emission direction of the partial radiation shield as a function of depth in the applicator. The shield contains three uniformly-distributed protruding keys on its exterior wall and is attached to the source such that it rotates freely, thus longitudinal translational motion of the source is transferred to rotational motion of the shield. RSBT treatment plans were generated for five cervical cancer patients with a diverse range of high-risk target volume (HR-CTV) shapes and applicator positions. Treatment delivery time and tumor coverage (D90 of HR-CTV) were the two metrics used as the basis for evaluation and comparison. With multi-source RSBT apparatus, precise angular and linear positioning of partially-shielded 153Gd brachytherapy sources in interstitial needles for the treatment of locally-advanced prostate cancer is carried out. Following needle implantation through the patient template, an angular drive mechanism is docked to the patient template. Each needle is coupled to a multisource afterloader catheter by a connector passing through a shaft. The shafts are rotated about their axes by translating a moving template between two stationary templates. Shafts’ surfaces and moving template holes are helically threaded with the same pattern such that translation of the moving template causes simultaneous rotation of the shafts. The catheter angles are simultaneously incremented throughout treatment. For each rotation angle, source depth in each needle is controlled by a multisource afterloader, which is proposed as an array of belt-driven linear actuators, each of which drives a wire that controls catheter depth in a needle. In conclusion, the helical RSBT approach for treating cervical cancer and the multi-catheter RSBT approach for treating prostate cancer, powered with novel radiation sources amenable to shielding, are clinically- and mechanically-feasible techniques that dosimetrically outperform conventional brachytherapy methods while minimizing damage to healthy tissues inside and/or adjacent to the target.

Current brachytherapy treatment planning systems are unable to accurately calculate dose distributions in the vicinity of brachytherapy sources having active lengths much greater than 5 mm. While low dose-rate ¹³⁷Cs sources are dosimetrically characterized using antiquated along-away tables with simple linear-linear interpolation errors in dose calculation exceeding 30% occur due to algorithm inadequacy. The method presented in this thesis permits dosimetric characterization of elongated brachytherapy sources with active lengths 0 < L < 10 cm for implementation on an FDA-approved clinical TPS. Low- and high-energy photon-emitting sources of Pd-103 and Ir-192, respectively, were examined.

Using the computer code Monte Carlo N-Particle (MCNP), doses were calculated for organs of interest such as the large intestine, urinary bladder, testes, and kidneys while patients were undergoing prostate brachytherapy. This research is important because the doses delivered to the prostate are extremely high and the organs near the prostate are potentially at risk for receiving high doses of radiation, leading to increased probabilities of adverse health effects such as cancer. In this research, two MCNP version 4C codes were used to calculate the imparted energies to the organs of interest delivered by 125I and 103Pd. As expected, the organs nearest to the prostate received the highest energy depositions and the organs farthest from the prostate received the lowest energy depositions. Once the energy depositions were calculated, the doses to the organs were calculated using the known volumes and densities of the organs. Finally, the doses to the organs over an infinite time period were calculated.

Prostate brachytherapy is a widely used treatment of localized prostate cancer. Intra-operative dose feedback would bring many benefits to patients and healthcare practitioners. Detection of brachytherapy seeds and segmentation of prostate boundaries play key roles in dosimetry for prostate brachytherapy. However, seed detection and prostate segmentation using conventional B-mode transrectal ultrasound still remains a challenge for prostate brachytherapy, mainly due to the small size of brachytherapy seeds in the relatively low-quality B-mode ultrasound images and due to the poor contrast between the prostate gland and surrounding tissues, speckle noise, shadowing and refraction artifacts. In this thesis, a new method called the reflected power imaging is presented to enhance the visibility and imaging of implanted seeds. It directly measures the reflected energy of ultrasound radio-frequency signals without logarithmic compression. Based on this method, we propose a new solution for brachytherapy seed detection in a 3D reflected power image computed from ultrasound radio-frequency signals, instead of conventional B-mode images. Then implanted seeds are segmented in 3D local search spaces that are determined by α priori knowledge, e.g. needle entry points and seed placements in a pre-operative dosimetry plan. Needle insertion tracks are also detected locally by using the Hough Transform. Experimental results show that the proposed solution works well for seed localization in a tissue-equivalent ultrasound prostate phantom implanted according to a realistic treatment plan with 136 seeds from 26 needles. As the prostate is a firm organ relative to surrounding tissues, elastography is a potential imaging modality for the guidance of prostate brachytherapy. A dynamic ultrasound elastography method named vibro-elastography can provide more complete dynamic tissue description in terms of transfer functions and coherence functions. In this thesis, we develop fast computational algorithms and programs to implement vibro-elastography imaging in real time. Phantom experiments demonstrate that the vibro-elastography techniques produce stable and operator-independent strain images with high contrast-to-noise ratio. Furthermore, the software for a 3D vibro-elastography imaging system has been designed, implemented and used in the data collection. Over 15 patients have been scanned at the British Columbia Cancer Agency, Vancouver Centre, and the results are encouraging.

Le cancer de la prostate est le cancer le plus fréquent chez l'homme en France et aux pays occidentaux. Il est la troisième cause de décès liés au cancer, étant responsable d'environ 10% des morts. La curiethérapie, une technique de radiothérapie, est liée à une meilleure qualité de vie après le traitement, par rapport aux autres méthodes de traitement. La curiethérapie de la prostate consiste à insérer des sources radioactives dans la prostate afin de délivrer une dose d'irradiation localisée à la tumeur tout en protégeant les tissus sains environnants. L'imagerie multimodale est utilisée afin d'améliorer la précision du traitement. Les images Tomodensitométriques préopératoires, appelées Computed Tomography (CT), peuvent être utilisées pour calculer une distribution personnalisée et plus précise de dose. Pendant l'intervention, le chirurgien utilise un système de guidage temps-réel par l'Ultrason Transrectale, Transrectal Ultrasound (TRUS), pour placer correctement les sources radioactives dans leurs positions souhaitées. Par conséquent, si les positions des sources sont déterminées sur l'image CT, elles doivent être transférées à l'image US. Cependant, un recalage US/CT direct et robuste est difficilement envisageable parce que les tissus mous, telle que la prostate, offrent peu de contraste en CT et en US. En revanche, l'Imagerie par Résonance Magnétique (IRM) fournit un meilleur contraste et peut, potentiellement, améliorer le traitement en améliorant la visualisation. Donc, ces trois modalités (IRM, CT et US) doivent être correctement alignées. Pour compenser les déformations de la prostate, due au changement de taille et forme entre les différentes acquisitions, un recalage non-rigide est nécessaire. Une méthode de recalage entièrement automatique est nécessaire, afin de faciliter son intégration au bloc opératoire. Nous proposons dans un premier temps un recalage IRM/CT basé sur la maximisation de l'information mutuelle en combinaison avec un champ de déformation paramétré par B-Splines. Nous proposons de contraindre le recalage sur des volumes d'intérêt (VOIs) afin d'améliorer la robustesse et le temps de calcul. L'approche proposée a été validée sur des jeux de données cliniques. Une évaluation quantitative a montré que l'erreur de recalage est égale à 1.15±0.20 mm; qui répond à la précision clinique souhaitée. Ensuite, nous proposons un deuxième recalage US/IRM, où nous utilisons une approche multi-résolution pour éviter les minima locaux et améliorer le temps de calcul. Un critère de similarité, qui met en corrélation l'intensité de l'image US avec l'intensité ainsi que le gradient de l'image IRM, a été utilisé afin de trouver la transformation qui aligne les deux images. Cette méthode a été validée sur un fantôme de prostate dans un premier temps pour évaluer sa faisabilité. Ensuite, elle a été validée sur des jeux de données cliniques en utilisant des critères qualitatives et quantitatives. La distance Hausdorff a montré que l'erreur de recalage est égale à 1.44±0.06 mm. L'approche proposée dans ce travail permet d'aller vers un protocole de curiethérapie guidée par l'imagerie multimodale qui puisse améliorer la précision globale de cette procédure. Malgré ces résultats plutôt encourageants, les travaux futurs impliqueront une évaluation plus approfondie sur plus de jeux de données afin d'évaluer la fiabilité et l'efficacité de cette méthode avant de l'intégrer au bloc opératoire
Prostate cancer is the most common cancer in men in France and western countries. It is the third leading cause of death from cancer, being responsible for around 10% of deaths. Brachytherapy, a radiotherapy technique, is associated with a better health-related quality of life after the treatment, compared to other treatment techniques. Prostate brachytherapy involves the implantation of radioactive sources inside the prostate to deliver a localized radiation dose to the tumor while sparing the surrounding healthy tissues. Multi-modal imaging is used in order to improve the overall accuracy of the treatment. The pre-operative Computed Tomography (CT) images can be used to calculate a personalized and accurate dose distribution. During the intervention, the surgeon utilizes a real-time guiding system, Trasnrectal Ultrasound (TRUS), to accurately place the radioactive sources in their desired pre-planned positions. Therefore, if the positions of the sources were determined on CT, they need to be transferred to US. However, a robust and direct US/CT registration is hardly possible since they both provide low soft tissue contrast. Magnetic Resonance Imaging (MRI), on the other hand, has a superior contrast and can potentially improve the treatment planning and delivery by providing a better visualization. Thus, these three modalities (MRI, US and CT) need to be accurately registered. To compensate for prostate deformations, caused by changes in size and form between the different acquisitions, non-rigid registration is essential. Fully automatic registration methodology is necessary in order to facilitate its integration in a clinical workflow. At first, we propose a registration between pre-operative MR and CT images based on the maximization of the mutual information in combination with a deformation field parameterized by cubic B-Splines. We propose to constrain the registration to volumes of interest (VOIs) in order to improve the robustness and the computational efficiency. The proposed approach was validated on clinical patient datasets. Quantitative evaluation indicated that the overall registration error was of 1.15±0.20 mm; which satisfies the desired clinical accuracy. Then, we propose a second intra-operative US/MRI registration, where a multi-resolution approach is implemented to reduce the probability of local minima and improve the computational efficiency. A similarity measure, which correlates intensities of the US image with intensities and gradient magnitude of the MRI, is used to determine the transformation that aligns the two images. The proposed methodology was validated on a prostate phantom at first to assess its feasibility. Subsequently, the method was validated on clinical patient datasets and evaluated using qualitative and quantitative criteria, resulting in a registration error of 1.44±0.06 mm. The approach proposed in this work allows going towards a multimodal protocol for image-guided brachytherapy which can improve the overall accuracy of this procedure. Despite such encouraging results, future work will involve further evaluation on a larger number of datasets in order to assess the reliability and the efficiency of this methodology before integrating it in a clinical workflow

Les procédures de radiothérapie visent à exposer les cellules cancéreuses aux rayonnements ionisants. L'implantation permanente de sources radioactives à proximité des cellules cancéreuses est une technique classique pour guérir le cancer de la prostate à un stade précoce. Le processus implique l'acquisition d'images du patient, la délimitation des volumes cibles et des organes à risque à l'aide de l'imagerie, la planification du traitement, l’implantation de grains radioactifs guidées par l'image et l'évaluation post-implantatoire. L'analyse d'images médicales basée sur l'intelligence artificielle peut être bénéfique pour des procédures de radiothérapie. Elle peut aider à faciliter et à améliorer l'efficacité des procédures en segmentant automatiquement les organes cibles les images et en extrapolant des informations cliniquement pertinentes. Cependant, la délimitation manuelle des volumes cibles est toujours la routine standard pour la plupart des centres cliniques, ce qui prend du temps et n'est pas à l'abri de variations intra et inter-observateurs. Dans cette thèse, nous visons à développer des solutions de traitement d'images médicales pour automatiser divers étapes des procédures actuelles de curiethérapie de la prostate guidée par l'image, notamment l'identification des grains radioactifs à partir d'images de scanner X et la segmentation du volume cible clinique à partir d'images médicales.Dans la première application, nous avons développé et évalué une nouvelle technique de détection et d'identification des grains radioactifs implantés sur des scanner X post-implantatoire en rapport avec la curiethérapie prostatique. Cela permet aux experts d'évaluer la qualité du positionnement de grains radioactifs guidées par l'image en calculant les paramètres dosimétriques, en particulier le calcul de dosimétrie post-implantoire de la curiethérapie de rattrapage de la prostate réalisée des années après la curiethérapie initiale dans le cadre de récidive de cancer de la prostate. La deuxième application impliquait le développement de méthodes d'apprentissage profond pour délimiter automatiquement les volumes cibles cliniques. Nous avons évalué les méthodes proposées sur une base de données cliniques d'échographie transrectale peropératoire et des images scanner X post-implantoires de la curiethérapie prostatique guidée par l'image. L'évaluation de notre méthode a été ensuite étendue à d'autres applications d'analyse d'images médicales. Nos méthodes ont donné des résultats prometteurs menant à une perspective essentielle pour des tâches d'analyse d'images médicales efficaces et précises. Elles peuvent être rebuvant être appliquées pour automatiser la gestion des procédures de curiethérapie prostatique guidée par l'image
Radiotherapy procedures aim at exposing cancer cells to ionizing radiation. Permanently implanting radioactive sources near to the cancer cells is a typical technique to cure early-stage prostate cancer. It involves image acquisition of the patient, delineating the target volumes and organs at risk on different medical images, treatment planning, image-guided radioactive seed delivery, and post-implant evaluation. Artificial intelligence-based medical image analysis can benefit radiotherapy procedures. It can help to facilitate and improve the efficiency of the procedures by automatically segmenting target organs and extrapolating clinically relevant information. However, manual delineation of target volumes is still the standard routine for most clinical centers, which is time-consuming, challenging, and not immune to intra- and inter-observer variations. In this thesis, we aim to develop medical image processing solutions to automate various components of the current image-guided prostate brachytherapy procedures, including radioactive seeds identification from CT images and clinical target volume segmentation from different medical images. In the first application, we developed and evaluated a new technique for detecting and identifying implanted radioactive seeds on post-implant CT scans of prostate brachytherapy. This allows experts to evaluate the quality of the image-guided radioactive seed delivery by computing the delivered dosimetric parameters, specifically to compute the post-implant dosimetry of salvage prostate brachytherapy performed years after primary brachytherapy in the treatment of relapsed prostate cancer. The second application involved the development of deep learning methods to delineate clinical target volumes automatically. We evaluated the proposed methods on a clinical database of intraoperative transrectal ultrasound and post-implant CT images of image-guided prostate brachytherapy. The evaluation is then extended to other medical image analysis applications. Our methods yielded promising results and opening important perspectives towards efficient and accurate medical image analysis tasks. They can be applied to automate the management of image-guided prostate brachytherapy procedures

Thesis (M.S.)--University of Florida, 2000.
Title from first page of PDF file. Document formatted into pages; contains ix, 38 p.; also contains graphics. Vita. Includes bibliographical references (p. 37).

In High Dose Rate (HDR) brachytherapy, treatment dose to patients is highly dependent on the accuracy of positioning and duration of the source. Source misplacement or wrong duration of treatment could potentially result in adverse clinical side effects to patients. In order to maintain successful treatment for patients, an independent Quality Assurance (QA) verification is crucial to measure the High Dose Rate (HDR) source positioning and dwell time periodically to ensure the prescribed dose is correct and safe for brachytherapy treatment. The current QA practice used to validate the accuracy of dwell time of the source is by using a stopwatch and measure the dwell position on the source position check ruler. Nevertheless, reaction time of human poses a major concern regarding the accuracy in these manual operating procedures. In this thesis, a new QA tool is proposed to acquire accurate information about time structure and source positioning in HDR brachytherapy. The tool consists of a consumer-grade webcam, a source position check ruler, a laptop computer and a custom-made combined camera-ruler mounting tool. The camera is used to capture the motion of the moving source in real time. Each frame contains positional and temporal information that are important to determine the difference between the measured and the actual HDR source position and time structure. Finally, a Graphical User Interface (GUI) application program is developed to receive the input from the camera for image processing. The measured results (time structure and positional information) are displayed on the computer screen as the output of the designed application. The tool was found to be able to reduce the time required significantly for the QA and minimize the impact of human errors. At the time of writing, the sensitivity of the system to luminous changes in the environment warrants further efforts to render the tool even more useful. Based on the experimental results, the accuracy of dwell time measured by the proposed system was ± 40 ms. The minimum detectable dwell time of the proposed system was 200 ms. The range of effective dwell position that could be measured by the system ranged from 1300 mm to 1500 mm (excluding 1300 mm and 1500 mm). The accuracy of dwell position measured by the proposed system was ± 1mm.
published_or_final_version
Diagnostic Radiology
Master
Master of Medical Sciences

A beta-emitting glass seed was proposed for the brachytherapy treatment of prostate cancer. Criteria for seed design were derived and several beta-emitting nuclides were examined for suitability. 142Pr was selected as the isotope of choice. Seeds 0.08 cm in diameter and 0.9 cm long were manufactured for testing. The seeds were activated in the Texas A&M University research reactor. The activity produced was as expected when considering the meta-stable state and epi-thermal neutron flux. The MCNP5 Monte Carlo code was used to calculate the quantitative dosimetric parameters suggested in the American Association of Physicists in Medicine (AAPM) TG-43/60. The Monte Carlo calculation results were compared with those from a dose point kernel code. The dose profiles agree well with each other. The gamma dose of 142Pr was evaluated. The gamma dose is 0.3 Gy at 1.0 cm with initial activity of 5.95 mCi and is insignificant to other organs. Measurements were performed to assess the 2-dimensional axial dose distributions using Gafchromic radiochromic film. The radiochromic film was calibrated using an X-ray machine calibrated against a National Institute of Standards and Technology (NIST) traceable ion chamber. A calibration curve was derived using a least squares fit of a second order polynomial. The measured dose distribution agrees well with results from the Monte Carlo simulation. The dose was 130.8 Gy at 6 mm from the seed center with initial activity of 5.95 mCi. AAPM TG-43/60 parameters were determined. The reference dose rate for 2 mm and 6 mm were 0.67 and 0.02 cGy/s/mCi, respectively. The geometry function, radial dose function and anisotropy function were generated.

This thesis describes experimental work performed (1998-2001) during the author's involvement with the Brachytherapy group at the Peter MacCallum Cancer Centre (PMCC), where he was employed by its Department of Physical Sciences and subsequent modeling and analytical studies. When PMCC added HDR brachytherapy to its radiation therapy practice, an existing operating suite was considered the ideal location for such procedures to be carried out. The integration of brachytherapy into the theatre environment was considered logical due to the relatively invasive nature of brachytherapy techniques and the availability of medical equipment. This thesis contains the detailed study of three key Research Questions involved in clinical aspects relating to quality assurance of an HDR brachytherapy practice. An investigative chapter is dedicated to the pursuit of each of the Research Questions. The first question asked… Is the novel approach to using modular shielding combined with time and distance constraints adequately optimized during HDR brachytherapy? In order to establish optimal clinical practices, this project evaluates the effectiveness of additional shielding added to the modular shielding system without modification of the previously determined time and distance constraints for PMCC staff, other patients, and member of the public. The DOSXYZnrc user code for the EGSnrc Monte Carlo radiation transport code has been used to model exposure pathways to strategic locations used for measurement in and around the operating theatre suite. Modeling allowed exposure pathways to various areas with the facility to be tested without the need to use real sources. The second Research Question asked… How well is dose anisotropy characterized in the near field range of the clinic's HDR 192Ir source? This study experimentally investigated the anisotropy of dose around a 192Ir HDR source in a water phantom using MOSFETs as relative dosimeters. In addition, modeling using the DOSRZnrc user code for the EGSnrc Monte Carlo radiation transport code was performed to provide a complete dose distribution consistent with the MOSFET measurements. Measurements performed for radial distances from 5 to 30 mm extend the range of measurements to 5 mm which has not been previously reported for this source construction. The third Research Question is aimed at the patient level. Is the dose delivered to in vivo dosimeters, located within critical anatomical structures near the prostate, within acceptable clinical tolerance for a large group of HDR prostate patients? An in vivo dosimetry technique employing TLDs to experimentally measure doses delivered to the urethra and rectum during HDR prostate brachytherapy was investigated. Urethral and rectal in vivo measurements for 56 patients have been performed in the initial fraction of four-fraction brachytherapy boost. In the absence of comparable in vivo data, the following local corrective action level was initially proposed: more than 50% of the prostatic urethra receiving a dose 10% beyond the urethral tolerance. The level for investigative action is considered from the analyses of dose differences between measured data and TPS calculation.

New approaches are urgently needed for treatment of cancer. The inherent heterogeneity of cells in solid tumors has thwarted most approaches developed to date. A fundamentally new approach, targeted molecular brachytherapy, also known as selective targeted amplified radiotherapy (S.T.A.R.), is attractive conceptually but has not yet been implemented. This new method selectively accumulates radioactive precipitates in tumor sites by systemic treatment of distinct agents in a sequential manner. One of the key agents for such a therapy is a soluble, precipitable reagent (SPR). The essence of this thesis includes design, synthesis and evaluation of porphyrin-based SPRs for the S.T.A.R. method. Three distinct designs of porphyrin-based SPRs were proposed. Synthetic approaches for target SPRs were explored, and several model compounds were synthesized. The development of a new synthetic approach to trans-AB-porphyrins, which are essential structures in the designs of SPRs, is also described in this thesis. Several target SPRs have not yet been synthesized due to synthetic difficulties as well as limitations related to water-solubility or stability of compounds. On the other hand, a diphosphate porphyrin exhibited successful enzymatic conversion from the water-soluble form to a porphyrin precipitate. Future work toward SPRs will focus on new designs that incorporate such diphosphate porphyrins.

Low dose rate prostate brachytherapy has emerged as a treatment option for localized prostate cancer. During prostate brachytherapy, tiny radioactive capsules - seeds - are implanted inside the tissue using long needles. The quality of the treatment depends on the accuracy of seed delivery to their desired positions. Prostate deformation and displacement during insertion and lack of sufficient visual feedback complicate accurate targeting and necessitates extensive training on the part of the physician. Needle insertion simulators can be useful for physician training. In addition, insertion of the needle with optimized parameters can compensate for prostate deformation, can decrease the targeting errors and, subsequently, can increase the post-treatment quality of life of the patients. Therefore, needle insertion simulation and path planning have gained a lot of attention in the research community in the past decade. Moreover, several robots have been designed for brachytherapy; however, they are yet to be coupled with proper needle insertion path planning algorithms. In this thesis, steps toward a path planning algorithm for needles are taken. An optimization method is proposed that updates the initial insertion parameters of a rigid needle, iteratively, based on the simulated positions of the targets, in order to reduce the error between the needle and several targets in a 3D tissue model. The finite element method is used in the needle insertion simulator. The simulator requires a model for the needle-tissue interaction. Therefore, an experimental method has been developed to identify the force model and the tissue elasticity parameters using measurements of insertion force, tissue displacement and needle position. Ultrasound imaging is used to measure tissue displacement. Ultrasound is a common imaging modality in the operating room and does not need beads or markers to track the tissue motion. Therefore, the experimental method can be used in patient studies. The needle-tissue modeling method and insertion parameter optimization were validated in experiments with tissue-mimicking phantoms. In order to facilitate the accommodation of needle flexibility for future applications, three flexible needle models have been compared. Based on these comparisons, it was determined that an efficient and accurate angular spring model is best suited for future studies.

In the UK, prostate cancer is the second most commonly occurring cancer in men.. The number of prostate cancer incidents is expected to increase due to improved screening and diagnostic techniques, whilst the mortality rate continues to fall as the variety ofavailable treatments increases. This research focuses on the commonly used brachytherapy seed OncoSeed™ Model 6711 manufactured by GE Healthcare. lodine-125 seeds are surgically implanted and left inside the prostate permanently to obtain local control of the malignant prostate cancer. Prior to the surgical procedure, a treatment plan is created on a computer planning system. There is currently no 3-D method to verify whether the planning system model matches the actual delivery ofradiation dose to the prostate. This study is presented as a typical case study of what can be achieved using solid polymer dosimetry. Experimental results are presented comparing solid polymer dosimetry using Optical-CT with radiochromic films (RCF) and Monte Carlo simulations. Initial Optical-CT results have shown good agreement to Monte Carlo, radiochromic films and comparable to previously published data.

Thesis (MTech (Radiography))--Cape Peninsula University of Technology, 2012
Introduction: Brachytherapy plays an essential role in the management of patients with cervical cancer. The high cervical cancer burden in Africa presents challenges with regard to provision and sustainability of these services. This study analysed treatment outcomes of two brachytherapy modalities, high dose rate (HDR) and low dose rate (LDR) intracavitary treatment for patients with cervical cancer, and evaluated the problems and challenges of the provision of these services within the African context. Methodology: The study was conducted using a case study approach with mixed methods at two sites in Africa, one in South Africa (Centre I) and the other in Kenya (Centre II). The study explored factors and issues affecting definitive radiotherapy of the patient with cervical cancer at the two sites with a focus on the brachytherapy treatment. The case study provided an opportunity to collect in-depth data consisting of quantitative and qualitative components that generated numeric and textual data. Treatment outcomes of one site treating with HDR and the other LDR intracavitary brachytherapy were retrospectively analysed for a maximum sample size of 193 (91%) patients in the HDR group and 49 (100%) patients in the LDR group. All patients were treated with external beam radiation therapy (EBRT) using parallel opposed beams (POP) for the patients that received LDR brachytherapy, and four field box technique or POP for those that received HDR brachytherapy. The linear quadratic formula was used to calculate the equivalent dose in 2 Gy fractions (EQD2) between the two groups.

L’objectif général de cette thèse est d’utiliser les connaissances en physique de la radiation, en programmation informatique et en équipement informatique à la haute pointe de la technologie pour améliorer les traitements du cancer. En particulier, l’élaboration d’un plan de traitement en radiothérapie peut être complexe et dépendant de l’utilisateur. Cette thèse a pour objectif de simplifier la planification de traitement actuelle en curiethérapie de la prostate à haut débit de dose (HDR). Ce projet a débuté à partir d’un algorithme de planification inverse largement utilisé, la planification de traitement inverse par recuit simulé (IPSA). Pour aboutir à un algorithme de planification inverse ultra-rapide et automatisé, trois algorithmes d’optimisation multicritères (MCO) ont été mis en oeuvre. Suite à la génération d’une banque de plans de traitement ayant divers compromis avec les algorithmes MCO, un plan de qualité a été automatiquement sélectionné. Dans la première étude, un algorithme MCO a été introduit pour explorer les frontières de Pareto en curiethérapie HDR. L’algorithme s’inspire de la fonctionnalité MCO intégrée au système Raystation (RaySearch Laboratories, Stockholm, Suède). Pour chaque cas, 300 plans de traitement ont été générés en série pour obtenir une approximation uniforme de la frontière de Pareto. Chaque plan optimal de Pareto a été calculé avec IPSA et chaque nouveau plan a été ajouté à la portion de la frontière de Pareto où la distance entre sa limite supérieure et sa limite inférieure était la plus grande. Dans une étude complémentaire, ou dans la seconde étude, un algorithme MCO basé sur la connaissance (kMCO) a été mis en oeuvre pour réduire le temps de calcul de l’algorithme MCO. Pour ce faire, deux stratégies ont été mises en oeuvre : une prédiction de l’espace des solutions cliniquement acceptables à partir de modèles de régression et d’un calcul parallèle des plans de traitement avec deux processeurs à six coeurs. En conséquence, une banque de plans de traitement de petite taille (14) a été générée et un plan a été sélectionné en tant que plan kMCO. L’efficacité de la planification et de la performance dosimétrique ont été comparées entre les plans approuvés par le médecin et les plans kMCO pour 236 cas. La troisième et dernière étude de cette thèse a été réalisée en coopération avec Cédric Bélanger. Un algorithme MCO (gMCO) basé sur l’utilisation d’un environnement de développement compatible avec les cartes graphiques a été mis en oeuvre pour accélérer davantage le calcul. De plus, un algorithme d’optimisation quasi-Newton a été implémenté pour remplacer le recuit simulé dans la première et la deuxième étude. De cette manière, un millier de plans de traitement avec divers compromis et équivalents à ceux générés par IPSA ont été calculés en parallèle. Parmi la banque de plans de traitement généré par l’agorithme gMCO, un plan a été sélectionné (plan gMCO). Le temps de planification et les résultats dosimétriques ont été comparés entre les plans approuvés par le médecin et les plans gMCO pour 457 cas. Une comparaison à grande échelle avec les plans approuvés par les radio-oncologues montre que notre dernier algorithme MCO (gMCO) peut améliorer l’efficacité de la planification du traitement (de quelques minutes à 9:4 s) ainsi que la qualité dosimétrique des plans de traitements (des plans passant de 92:6% à 99:8% selon les critères dosimétriques du groupe de traitement oncologique par radiation (RTOG)). Avec trois algorithmes MCO mis en oeuvre, cette thèse représente un effort soutenu pour développer un algorithme de planification inverse ultra-rapide, automatique et robuste en curiethérapie HDR.
L’objectif général de cette thèse est d’utiliser les connaissances en physique de la radiation, en programmation informatique et en équipement informatique à la haute pointe de la technologie pour améliorer les traitements du cancer. En particulier, l’élaboration d’un plan de traitement en radiothérapie peut être complexe et dépendant de l’utilisateur. Cette thèse a pour objectif de simplifier la planification de traitement actuelle en curiethérapie de la prostate à haut débit de dose (HDR). Ce projet a débuté à partir d’un algorithme de planification inverse largement utilisé, la planification de traitement inverse par recuit simulé (IPSA). Pour aboutir à un algorithme de planification inverse ultra-rapide et automatisé, trois algorithmes d’optimisation multicritères (MCO) ont été mis en oeuvre. Suite à la génération d’une banque de plans de traitement ayant divers compromis avec les algorithmes MCO, un plan de qualité a été automatiquement sélectionné. Dans la première étude, un algorithme MCO a été introduit pour explorer les frontières de Pareto en curiethérapie HDR. L’algorithme s’inspire de la fonctionnalité MCO intégrée au système Raystation (RaySearch Laboratories, Stockholm, Suède). Pour chaque cas, 300 plans de traitement ont été générés en série pour obtenir une approximation uniforme de la frontière de Pareto. Chaque plan optimal de Pareto a été calculé avec IPSA et chaque nouveau plan a été ajouté à la portion de la frontière de Pareto où la distance entre sa limite supérieure et sa limite inférieure était la plus grande. Dans une étude complémentaire, ou dans la seconde étude, un algorithme MCO basé sur la connaissance (kMCO) a été mis en oeuvre pour réduire le temps de calcul de l’algorithme MCO. Pour ce faire, deux stratégies ont été mises en oeuvre : une prédiction de l’espace des solutions cliniquement acceptables à partir de modèles de régression et d’un calcul parallèle des plans de traitement avec deux processeurs à six coeurs. En conséquence, une banque de plans de traitement de petite taille (14) a été générée et un plan a été sélectionné en tant que plan kMCO. L’efficacité de la planification et de la performance dosimétrique ont été comparées entre les plans approuvés par le médecin et les plans kMCO pour 236 cas. La troisième et dernière étude de cette thèse a été réalisée en coopération avec Cédric Bélanger. Un algorithme MCO (gMCO) basé sur l’utilisation d’un environnement de développement compatible avec les cartes graphiques a été mis en oeuvre pour accélérer davantage le calcul. De plus, un algorithme d’optimisation quasi-Newton a été implémenté pour remplacer le recuit simulé dans la première et la deuxième étude. De cette manière, un millier de plans de traitement avec divers compromis et équivalents à ceux générés par IPSA ont été calculés en parallèle. Parmi la banque de plans de traitement généré par l’agorithme gMCO, un plan a été sélectionné (plan gMCO). Le temps de planification et les résultats dosimétriques ont été comparés entre les plans approuvés par le médecin et les plans gMCO pour 457 cas. Une comparaison à grande échelle avec les plans approuvés par les radio-oncologues montre que notre dernier algorithme MCO (gMCO) peut améliorer l’efficacité de la planification du traitement (de quelques minutes à 9:4 s) ainsi que la qualité dosimétrique des plans de traitements (des plans passant de 92:6% à 99:8% selon les critères dosimétriques du groupe de traitement oncologique par radiation (RTOG)). Avec trois algorithmes MCO mis en oeuvre, cette thèse représente un effort soutenu pour développer un algorithme de planification inverse ultra-rapide, automatique et robuste en curiethérapie HDR.
The overall purpose of this thesis is to use the knowledge of radiation physics, computer programming and computing hardware to improve cancer treatments. In particular, designing a treatment plan in radiation therapy can be complex and user-dependent, and this thesis aims to simplify current treatment planning in high dose rate (HDR) prostate brachytherapy. This project was started from a widely used inverse planning algorithm, Inverse Planning Simulated Annealing (IPSA). In order to eventually lead to an ultra-fast and automatic inverse planning algorithm, three multi-criteria optimization (MCO) algorithms were implemented. With MCO algorithms, a desirable plan was selected after computing a set of treatment plans with various trade-offs. In the first study, an MCO algorithm was introduced to explore the Pareto surfaces in HDR brachytherapy. The algorithm was inspired by the MCO feature integrated in the Raystation system (RaySearch Laboratories, Stockholm, Sweden). For each case, 300 treatment plans were serially generated to obtain a uniform approximation of the Pareto surface. Each Pareto optimal plan was computed with IPSA, and each new plan was added to the Pareto surface portion where the distance between its upper boundary and its lower boundary was the largest. In a companion study, or the second study, a knowledge-based MCO (kMCO) algorithm was implemented to shorten the computation time of the MCO algorithm. To achieve this, two strategies were implemented: a prediction of clinical relevant solution space with previous knowledge, and a parallel computation of treatment plans with two six-core CPUs. As a result, a small size (14) plan dataset was created, and one plan was selected as the kMCO plan. The planning efficiency and the dosimetric performance were compared between the physician-approved plans and the kMCO plans for 236 cases. The third and final study of this thesis was conducted in cooperation with Cédric Bélanger. A graphics processing units (GPU) based MCO (gMCO) algorithm was implemented to further speed up the computation. Furthermore, a quasi-Newton optimization engine was implemented to replace simulated annealing in the first and the second study. In this way, one thousand IPSA equivalent treatment plans with various trade-offs were computed in parallel. One plan was selected as the gMCO plan from the calculated plan dataset. The planning time and the dosimetric results were compared between the physician-approved plans and the gMCO plans for 457 cases. A large-scale comparison against the physician-approved plans shows that our latest MCO algorithm (gMCO) can result in an improved treatment planning efficiency (from minutes to 9:4 s) as well as an improved treatment plan dosimetric quality (Radiation Therapy Oncology Group (RTOG) acceptance rate from 92.6% to 99.8%). With three implemented MCO algorithms, this thesis represents a sustained effort to develop an ultra-fast, automatic and robust inverse planning algorithm in HDR brachytherapy.
The overall purpose of this thesis is to use the knowledge of radiation physics, computer programming and computing hardware to improve cancer treatments. In particular, designing a treatment plan in radiation therapy can be complex and user-dependent, and this thesis aims to simplify current treatment planning in high dose rate (HDR) prostate brachytherapy. This project was started from a widely used inverse planning algorithm, Inverse Planning Simulated Annealing (IPSA). In order to eventually lead to an ultra-fast and automatic inverse planning algorithm, three multi-criteria optimization (MCO) algorithms were implemented. With MCO algorithms, a desirable plan was selected after computing a set of treatment plans with various trade-offs. In the first study, an MCO algorithm was introduced to explore the Pareto surfaces in HDR brachytherapy. The algorithm was inspired by the MCO feature integrated in the Raystation system (RaySearch Laboratories, Stockholm, Sweden). For each case, 300 treatment plans were serially generated to obtain a uniform approximation of the Pareto surface. Each Pareto optimal plan was computed with IPSA, and each new plan was added to the Pareto surface portion where the distance between its upper boundary and its lower boundary was the largest. In a companion study, or the second study, a knowledge-based MCO (kMCO) algorithm was implemented to shorten the computation time of the MCO algorithm. To achieve this, two strategies were implemented: a prediction of clinical relevant solution space with previous knowledge, and a parallel computation of treatment plans with two six-core CPUs. As a result, a small size (14) plan dataset was created, and one plan was selected as the kMCO plan. The planning efficiency and the dosimetric performance were compared between the physician-approved plans and the kMCO plans for 236 cases. The third and final study of this thesis was conducted in cooperation with Cédric Bélanger. A graphics processing units (GPU) based MCO (gMCO) algorithm was implemented to further speed up the computation. Furthermore, a quasi-Newton optimization engine was implemented to replace simulated annealing in the first and the second study. In this way, one thousand IPSA equivalent treatment plans with various trade-offs were computed in parallel. One plan was selected as the gMCO plan from the calculated plan dataset. The planning time and the dosimetric results were compared between the physician-approved plans and the gMCO plans for 457 cases. A large-scale comparison against the physician-approved plans shows that our latest MCO algorithm (gMCO) can result in an improved treatment planning efficiency (from minutes to 9:4 s) as well as an improved treatment plan dosimetric quality (Radiation Therapy Oncology Group (RTOG) acceptance rate from 92.6% to 99.8%). With three implemented MCO algorithms, this thesis represents a sustained effort to develop an ultra-fast, automatic and robust inverse planning algorithm in HDR brachytherapy.

Patients with cervical cancer are treated both with external beam radiotherapy(EBRT) and brachytherapy (BT) which involves an applicator. During the treatments, CT-images are taken and to perform dose calculations, deformable image registration (DIR) is performed. The image registration involves many challenges, for example, the organs may have different shapes and volumes in the images and the images have different intensities due to the applicator. Many DIR-methods are available but they fail in aligning the multiple organs correctly and simultaneously. This project aimed for developing a method that created triangle meshes of the rectum and bladder in EBRT- and BT-images.The generation of triangle meshes was driven by projection points on the organ and found pairs of points between the same organ in both images. The performance of using these triangle meshes in DIR was compared with that of using boundary conditions (also triangle meshes) and binary masks. Results show that the triangle meshes and boundary conditions performed similarly concerning the DSC, mean DTA and HD validated on rectum, bladder and bones, while the binary masks performed the worst. For the TRE results of the projection points, the triangle meshes outperformed the boundary conditions which shows potential for this method. One drawback of this method is its sensitivity to the initialization for generating triangle meshes, which can be improved. In its developing state, the method has proven to perform well but it remains to see how well it performs on other organs, such as the vagina, cervix and uterus combined and sigmoid.
Patienter med livmoderhalscancer behandlas med både extern strålterapi och brachyterapi vilket involverar en applikator. Under behandlingarna tas CT-bilder och för att beräkna stråldoserna genomförs deformabel bildregistrering. Bildregistreringen innebär många utmaningar, till exempel kan organen ha olika former och volymer i bilderna och bilderna har olika intensiteter på grund av applikatorn. Det finns många metoder som utför deformabel bildregistrering, men dessa misslyckas med att kunna deformera flera organkorrekt och samtidigt. Detta projekt strävade efter att utveckla en metod som skapade triangel meshar av ändtarmen och urinblåsan i båda bilderna. Skapandet av triangel mesharna drevs av projektionspunkter på organensamt funna par av punkter mellan samma organ i båda bilderna. Resultatet av att använda triangel mesharna i deformabel bildregistrering jämfördes med att använda så kallade “boundary conditions"(även de triangel meshar)och binära masker, vilket är de segmenterade organen. Resultatet visade att triangel mesharna och “boundary conditions" var lika bra sett till DSC, medel DTA och HD validerade på ändtarmen, urinblåsan och skelettet medan binära maskar presterade sämst. För TRE resultatet av projektionspunkterna var det triangel mesharna som överträffade “boundary conditions", vilket visarpotential för denna metod. En nackdel med denna metod är att den är känsligför initialiseringen för att skapa triangel mesharna, vilket kan förbättras. I utvecklingsstadiet har metoden presterat väl, men det återstår att se hur väldet presterar för andra organ, exempelvis vagina, cervix tillsammans medlivmoder, och sigmoid.

In the past twenty years, the combination of the advances in medical imaging technologies and therapeutic methods had a great impact in developing minimally invasive interventional procedures. Although the use of medical imaging for the surgery and therapy guidance dates back to the early days of x-ray discovery, there is an increasing evidence in using the new imaging modalities such as computed tomography (CT), magnetic reso- nance imaging (MRI) and ultrasound in the operating rooms. The focus of this thesis is on developing image-guided interventional methods and techniques to support the radiation therapy treatment of gynecologic cancers. Gynecologic cancers which involves malignan- cies of the uterus, cervix, vagina and the ovaries are one of the top causes of mortality and morbidity among the women in U.S. and worldwide. The common treatment plan for radiation therapy of gynecologic cancers is chemotherapy and external beam radiation therapy followed by brachytherapy. Gynecological brachytherapy involves placement of interstitial catheters in and around the tumor area, often with the aid of an applicator. The goal is to create an optimal brachytherapy treatment plan that leads to maximal radiation dose to the cancerous tissue and minimal destructive radiation to the organs at risk. The accuracy of the catheter placement has a leading effect in the success of the treatment. However there are several techniques are developed for navigation of catheters and needles for procedures such as prostate biopsy, brain biopsy, and cardiac ablation, it is obviously lacking for gynecologic brachytherapy procedures. This thesis proposes a technique which aims to increase the accuracy and efficiency of catheter placements in gynecologic brachytherapy by guiding the catheters with an electromagnetic tracking system. To increase the accuracy of needle placement a navigation system has been set up and the appropriate software tools were developed and released for the public use as a module in the open-source 3D Slicer software. The developed technology can be translated from benchmark to the bedside to offer the potential benefit of maximizing tumor coverage during catheter placement while avoiding damage to the adjacent organs including bladder, rectum and bowel. To test the designed system two independent experiments were designed and performed on a phantom model in order to evaluate the targeting accuracy of the tracking system and the mean targeting error over all experiments was less than 2.9 mm, which can be compared to the targeting errors in the available commercial clinical navigation systems.

Intensity-modulated brachytherapy techniques, compensator-based intensity modulated brachytherapy (CBT) and interstitial rotating shield brachytherapy (I-RSBT), are two novel conceptual radiation therapies for treating cervical and prostate cancer, respectively. Compared to conventional brachytherapy techniques for treating cervical cancer, CBT can potentially improve the dose conformity to the high-risk clinical target volume (CTV) of the cervix in a less invasive approach. I-RSBT can reduce the dose delivered to the prostate organ at risks (OARs) with the same radiation dose delivered to the prostate CTV. In this work, concepts and prototypes for CBT and I-RSBT were introduced and developed. Preliminary dosimetric measurements were performed for CBT and I-RSBT, respectively. A CBT prototype system was constructed and experimentally validated. A prototype cylindrical compensator with eight octants, each with different thicknesses, was designed. Direct metal laser sintering (DMLS) was used to construct CoCr and Ti compensator prototypes, and a 4-D milling technique was used to construct a Ti compensator prototype. Gafchromic EBT2 films, held by an acrylic quality assurance (QA) phantom, were irradiated to approximately 125 cGy with an electronic brachytherapy (eBT) source for both shielded and unshielded cases. The dose at each point on the films were calculated using a TG-43 calculation model that was modified to account for the presence of a compensator prototype by ray-tracing. With I-RSBT, a multi-pass dose delivery mechanism with prototypes was developed. Dosimetric measurements for a Gd-153 radioisotope was performed to demonstrate that using multiple partially shielded Gd-153 sources for I-RSBT is feasible. A treatment planning model was developed for applying I-RSBT clinically. A custom-built, stainless steel encapsulated 150 mCi Gd-153 capsule with an outer length of 12.8 mm, outer diameter of 2.10 mm, active length of 9.98 mm, and active diameter of 1.53 mm was used. A partially shielded catheter was constructed with a 500 micron platinum shield and a 500 micron aluminum emission window, both with 180° azimuthal coverage. An acrylic phantom was constructed to measure the dose distributions from the shielded catheter in the transverse plane using Gafchromic EBT3 films. Film calibration curves were generated from 50, 70, and 100 kVp x-ray beams with NIST-traceable air kerma values to account for energy variation. In conclusion, CBT, which is a non-invasive alternative to supplementary interstitial brachytherapy, is expected to improve dose conformity to bulky cervical tumors relative to conventional intracavitary brachytherapy. However, at the current stage, it would be time-consuming to construct a patient-specific compensator using DMLS, and the quality assurance of the compensator would be difficult. I-RSBT is a promising approach to reducing radiation dose delivered to prostate OARs. The next step in making Gd-153 based I-RSBT feasible in clinic is developing a Gd-153 source that is small enough such that the source, shield, and catheter all fit within a 16 guage needle, which has a 1.65 mm diameter.

Purpose

Individual optimized treatment planning is recommended when creating treatment plans for brachytherapy of cervical cancer. Manual alteration of the dose distribution is time consuming and the treatment plan may be dependent on the person creating it. Inverse planning simulated anneahng (IPSA) is an algorithm that can optimize the dose distribution considering dose to several delineated structures. This algorithm, currently available in the treatment planning system Masterplan, has been evaluated for brachytherapy of cervical cancer. The Masterplan system simulates a source type from at different manufacturer than the type used for treatment at St. Olavs Hospital at the time being. The dose distribution from the two source types were evaluated to see if Masterplan an be used to simulate the source type used for treatment at St. Olavs Hospital.

Methods and materials

The dose distributions from the two source types were compared based on calcuations from two treatment planning systems (Masterplan and Plato) simulating each source type.

Dose measurements of the source used at St. Olavs Hospital for brachytherapy treatment of cervical cancer were taken. These were compared with the dose distribution calculated by the two treatment planning systems.

At St. Olavs Hospital treatment are executed using a Fletcher type applicator. MR-images are taken with the applicator in place. Target and organs at risk are delineated in the images before the treatment planning is performed. For 11 patients treated with brachytherapy of cervical cancer at St. Olavs Hospital, three different IPSA-plans with different dose constraints (IPSA1, IPSA2 and IPSA3) and one treatment plan with equal dwell times were made in retrospect. All IPSA-plans constrain the same dose to the target. IPSA1 and IPSA3 have the same constraints to organs at risk, while IPSA2 allow a higher dose to the organs at risk. IPSA3 sets a limit for maximum dose in target volume. For evaluation of the quality of the treatment plans, dose parameters of chnical relevance were extracted from dose volume histograms.

Results

Deviations in the calculated dose distribution up to 30% is found for the two source types in certain areas. These deviations are found close to the source and below the connector end of the source. For distances ≥ 4 mm from the source center along one axis, deviations of the calculations were ≤ 4%. This is in correspondance with the measured dose values.

Target coverage for IPSA2 is 0.92. For IPSA1 and IPSA3 target coverage is 0.84 and 0.81 respectively. The number of treatment plans exceeding tolerance limit for one or more OAR is 82% for IPSA2, 55% for IPSA1 and 35% for IPSA3. The plan with equal dwell times have a target coverage of 0.66 and 45% of the treatment plans exceed the given tolerance limit for one or more organs at risk.

Conclusion

Deviations are found in the simulated dose distribution of the two source types tested, but only in clinical irrelevant areas for brachytherapy of cervical cancer. Masterplan can be used for simulating the dose distribution of the source used for treatment at St. Olavs Hospital.

Using IPSA is better when it comes to improving target coverage and not violating tolerance limit for organs at risk, than a conservative treatment plan with equal dwell times. Due to too high doses to organs at risk, IPSA2 should be rejected. IPSA1 has better target coverage and IPSA3 have lower dose to the organs at risk. To avoid inhomogeneities in dwell time values, IPSA3 is probably the best suggestion.

 

Sammendrag

Formål

Det er anbefalt & lage individuelt optimaliserte plan når behandlingsplaner skal lages i forbindelse med brachyterapi av livmorhalskreft. Manuell endring av dosefordelingen er tidkrevende og resultatet kan bli preget av personen som lager planen. 'Iverse planning simulated anneahng' (IPSA) er en algoritme som kan optimalisere dosefordehngen slik at dose til flere skisserte strukturer blir tatt hensyn til. Denne algoritmen, tilgjengehg i doseplanleggingssystemet Masterplan, har blitt vurdert for brachyterapi av livmorhalskreft.

Masterplan simulerer en kildetype fra en annen produsent enn den kildetypen som blir brukt til behandling på St. Olavs hospital i dag. Dosefordehngen til de to kildetypene har blitt vurdert for å se om Masterplan kan brukes til å simulere kildetypen brukt til behandling.

Metode og utstyr

Dosefordehngen fra de to kildetypene ble sammenlignet ved hjelp av doseberegninger fra to doseplanleggingssystemer (Masterplan og Plato) som simulerer hver sin kildetype.

Det ble tatt målinger av dosen fra kilden brukt på St. Olavs hospital til brachyterapi av livmorhalskreft. Disse ble sammenlignet med dosefordelingen regnet ut av de to planleggingssystemene.

På St. Olavs hospital blir en Fletcher type apphkator brukt til behandling. MR-bilder blir tatt etter at applikatoren er posisjonert. I bildene blir målvolum og risikooganer skissert før behandlingsplanleggingen gjennomføres. I denne studien har tre ulike IPSA-planer med forskjellig doserestriksjoner (IPSA1, IPSA2 and IPSA3) og en plan med lik liggetid i kildeposisjonene, blitt laget i ettertid for 11 pasienter behandlet for livmorhalskreft på St. Olavs hospital. IPSA-planene har samme doserestriksjoner til målvolum. IPSA1 og IPSA3 har samme begrensning til risikoorganer, mens IPSA2 tillater høyere dose til risikoorganer. IPSA3 har en begrensning for maksimum dose til volum for måvolumet. For vurdering av kvaliteten til planene ble klinisk relevante doseparametre funnet fra dosevolum-histogram.

Resultat

Det ble funnet avvik opp til 30% for beregnet dose i ulike punkt for de to kildetypene i visse omr&der. Disse avvikene ligger nærme kilden og rett under koblingsenden. For avstander ≥ 4 mm fra kildesenter transversalt på kilden er avvikene i beregningene ≤4%. Dosemålingene som ble tatt støtter dette.

Dekning av målvolum er 0.92 for IPSA2. For IPSA1 og IPSA3 er denne dekninjen henholdsvis 0.84 og 0.81. Antall planer hvor en definert grense for dosen til et eller flere risikoorgan har blitt oversteget, er 82% for IPSA2, 55% for IPSA1 og 35% for IPSA3. Planen hvor liggetidene er fordelt likt har malvolumdekning på 0.66 og 45% av planene overstiger den definerte toleranse grensen for et eller flere risikoorgan.

Konklusjon

Det ble funnet avvik i de simulerte dosefordelingene mellom de to kildetypene, men kun i klinisk irrelevante områder for brachyterapi av livmorhalskreft. Masterplan kan bli brukt til å simulere dosefordelingen til kilden som blir brukt til behandling på St. Olavs hospital.

Bruk av IPSA gir bedre resultater enn den konservative behandlingsplanen med lik liggetid ncir det gjelder dekning av målvolum og å overholde toleransegrensene som er satt for risikorganene. På grunn av for høye doser til risikoorganer burde IPSA2 forkastes. IPSA3 gir bedre dekning av måvolum mens IPSA3 gir lavere dose til risikoorganer. For å unngå store forskjeller mellom liggetidene i de ulike kildeposisjonene vil antagelig IPSA3 gi best utganspunkt for videre planlegging.

Radiation therapy in the definitive treatment of locally advanced carcinoma of the cervix consists of external beam radiotherapy (EBRT) combined with image-guided high-dose-rate (IG HDR) intracavitary brachytherapy (ICBT). IG HDR-ICBT is a relatively new, advanced form of brachytherapy treatment planning and delivery that still relies largely on dose criteria based either on clinical experience using older techniques, or on limited data. Calculation of cumulative dose received over multiple treatment fractions currently utilizes dose-volume-histograms (DVH), which do not provide information about the spatial distribution of dose within the structures of interest. Since most of the organs at risk (OAR) for this site, like the bladder and rectum, are highly deformable, DVH data summed over multiple treatment fractions do not provide accurate estimates of the cumulative dose to specific regions of the organ, and therefore may not be the most appropriate metric to use in treatment planning and dose assessment. The primary goal of this thesis was, therefore, to develop methods to more accurately quantify “locally accumulated” dose to the bladder-wall in multi-fraction IG HDR-ICBT for cervical cancer using deformable registration, and to apply these to a study of locally-accumulated dosimetric parameters as predictors of late urinary toxicity. To this end, different deformable image and point-set registration methods were evaluated, using phantom data, for their ability to register bladder-wall contours of various sizes. The best of these was retrospectively applied to point-sets representing the bladder-wall in multiple HDR treatment fractions for 60 cervical cancer patients treated at the BC Cancer Agency. The transformation maps obtained from the registrations were used to calculate cumulative dose parameters for the bladder-wall and the urethral opening to the bladder (bladder neck). Patients were divided into Case and Control groups based on urinary toxicity scores for different symptoms, and the ability of the cumulative parameters to predict toxicity was evaluated. It was concluded that some locally-cumulative parameters estimated using our method have improved potential for predicting urinary toxicity, as compared to traditional DVH-based parameters, in our data set. In addition, dose to small volumes around the bladder neck was found to be a predictor of incontinence.
Science, Faculty of
Graduate

The aim of this study is to develop an intraoperative dose assessment procedure that can be performed after an I-125 prostate seed implantation, while the patient is still under anaesthesia. To accomplish this, we reconstruct the 3D position of each seed and co-register it with the prostate contour acquired with a transrectal ultrasound (TRUS) probe. Our seed detection method involves a tomosynthesis-based filtered reconstruction of the volume of interest requiring 7 projections acquired over an angle of 60o with an isocentric imaging system. The co-registration between the tomosynthesis-based seed positions and the TRUS-based prostate contour is based on the planned position. A phantom and a clinical study (25 patients) were carried out to validate the technique. In the patient study, the automatic tomosynthesis-based reconstruction yields a seed detection rate of 96.7% and less than 2.6% false-positive. The seed localization error obtained with a phantom study is 0.4 ± 0.4 mm. The co-registration method based on planned seed position has proved to be not accurate enough for dosimetric purposes. We believe that this technique may be used to discover considerable underdosage and to improve the dosimetric coverage by potentially reimplanting additional seeds.
L'objectif de ce projet est de développer une procédure d'évaluation dosimétrique intra-opératoire en implantation prostatique de grains d'iode 125. Pour y arriver, la position 3D des grains doit être reconstruite et recalée avec les contours de la prostate imagée en échographie endorectale. La reconstruction des grains est basée sur une technique de tomosynthèse requérant 7 projections acquises entre -30o et 30o. Le recalage entre la position 3D des grains et les contours utilise comme cible la position planifiée des grains. Notre technique de reconstruction dosimétrique a été testée sur un mannequin et dans une étude clinique incluant 25 patients. Notre méthode permet de reconstruire la position 3D des grains avec une précision de 0.4 ± 0.4 mm. De plus, l'étude clinique a démontré un taux de détection de 96.7% des grains et incluant moins de 2.6% de faux-positifs. La méthode de recalage n'a pas permis d'atteindre une précision acceptable pour une application clinique. La technique développée permet de repérer la présence de sous-dosage considérable et ouvre la porte vers la réimplantation de grains additionnels afin d'améliorer la couverture dosimétrique de la prostate.