Academic literature on the topic 'Radiotherapy and oncology'

Organ motion - whether due to respiration, cardiac motion or digestive processes - is one of the major problems in external beam radiotherapy as it limits the achievable precision in dose delivery. Adaptive radiotherapy (ART) is a novel approach for a more precise dose delivery where measured patient-specific variations are used to change the delivery pattern throughout the treatment course. The aim of the work described in this thesis has been to contribute to the progress of ART by developing dynamic phantoms for the simulation of target motion, evaluating adaptive treatment strategies, and providing tools for the assessment of optimal patient-specific treatment parameters. A dynamic, anthropomorphic and tissue equivalent thorax phantom has been developed and assessed. The phantom provides accurate, three-dimensional regular or irregular motion of both a tumour within the lungs and the chest wall independently. It has been designed to investigate the effect of organ motion on the dose delivered to a moving target, to evaluate the potential benefit of adaptive treatment strategies and to assess ART delivery systems. The potential of the phantom has been evaluated through experiments on a respiratory-gated CT system and during tests on a real-time motion tracking system. In addition, the principles used for the thoracic phantom have been used to design dynamic phantoms for the prostate and bladder. An adaptive off-line correction strategy accounting for inter-fractional prostate motion has been evaluated using radiobiological modelling. This work revealed that it is important to consider the normal tissue complication probability of the rectum and the direction of anterior-posterior prostate motion when determining the optimal timing for re-optimisation of the treatment plan. Specifically, relying on calculations of the tumour control probability alone provides misleading results. In general off-line correction based on only a few observations in the early treatment course is shown to improve the probability of uncomplicated tumour control. Target coverage for respiratory-gated radiotherapy has been modelled with simulated and real breathing traces. The results have demonstrated that maximum benefit is achieved with amplitude gating at end of exhalation. The analysis showed that treatment parameters should be adjusted prior to each fraction. As part of this work a model that assists on deciding the most appropriate gating parameters on an individual patient basis has been developed. Finally, a treatment strategy decision support tool has been developed and applied to respiratory data obtained from patients. The tool not only identifies whether tumour mobility justifies implementing an adaptive treatment technique but where it does the tool supports selecting the optimal ART technique to be used together with the appropriate treatment parameters that will provide the greatest benefit to an individual lung cancer patient.

External beam radiation therapy (EBRT) is the most common form of radiation therapy (RT) that uses controlled energy sources to eradicate a predefined tumour volume, known as the planning target volume (PTV), whilst at the same time attempting to minimise the dose delivered to the surrounding healthy tissues. Tumours in the thoracic and abdomen regions are susceptible to motion caused mainly by the patient respiration and movement that may occur during the treatment preparation and delivery. Usually, an adaptive approach termed adaptive radiation therapy (ART), which involves feedback from imaging devices to detect organ/surrogate motion, is considered. The feasibility of such techniques is subject to two main problems. First, the exact position of the tumour has to be estimated/detected in real-time and second, the delay that can arise from the tumour position acquisition and the motion tracking compensation. The research work described in this thesis is part of the European project entitled ‘Methods and advanced equipment for simulation and treatment in radiation oncology’ (MAESTRO), see Appendix A. The thesis presents both theoretical and experimental work to model and predict the respiratory surrogate motion. Based on a widely investigated clinical internal and external respiratory surrogate motion data, two new approaches to model respiratory surrogate motion were developed. The first considers the lung as a bilinear model that replicates the motion in response to a virtual input signal that can be seen as a signal generated by the nervous system. This model and a statistical model of the respiratory period and duty cycle were used to generate a set of realistic respiratory data of varying difficulties. The aim of the latter was to overcome the lack of test data for a researcher to evaluate their algorithms. The second approach was based on an online polynomial function that was found to adequately replicate the breathing cycles of regular and irregular data, using the same number of parameters as a benchmark sinusoidal model.

It is known that slight variations in total dose delivered to the patient in external beam photon radiotherapy can significantly alter the probability of tumour control. For this reason, ICRU has recommended a goal of $ pm$5% precision in the dose delivery to the target volume. Several investigators have analyzed the degree of precision routinely achieved and have come to the conclusion that ICRU's goal can be attained, but in practice this is just barely so.<br>We have measured the degree of precision which exists in our institution by examining each step of the radiotherapy process on a cobalt unit and a 10 MV linear accelerator. Our study finds beam intensity uncertainties of $ pm$3.8% (one standard deviation) and beam positional uncertainties of $ pm$5.5 mm (one standard deviation). The effect of these uncertainties on the dose to the patient is illustrated for a typical case.

The hypothesis of this work was whether IGRT could be safely implemented for clinical use in a busy oncology centre. I aimed to study a number of questions that remain unresolved in the current literature regarding safe and optimised implementation of IGRT techniques. The first study undertaken was the calculation of a local set up margin using two widely recognised margin recipes. This involved the assessment and analysis of multiple images belonging to 100 patients. This allowed progression onto the next project which was assessment of the optimal safe method of delineation of 4DCT. The most efficient method was compared to gold standard. At this point a different aspect of the radiation process was assessed, namely verification. A feasibility study of a simple, efficient form of imaging for use in review of a particular error was performed. This also involved the use of a novel tool which required independent assessment. This progressed into a further study of a larger number of patients using this tool and the images assessed previously to verify a novel form of radiation delivery. Lastly a planning study was performed to quantify the clinical benefit of another delivery system. This involved the delineation and planning of a large number of radical lung patients with standard radiation treatment and the novel radiation treatment and an assessment of the potential clinical benefits. The work presented in this thesis has answered some specific questions in IGRT in lung cancer, and contributed both locally and in the wider lung cancer community to increasing the use of IGRT in lung cancer.

Background Accurate delivery of radiotherapy is a paramount component of providing safe oncological care. Margins are applied when planning radiotherapy to account for subclinical tumour spread, physiological movement and set-up error. Set-up error is unique to each radiotherapy institution and should be calculated for each organ site to ensure safe delivery of treatment. Aim and setting The aim of this study is to calculate the random and systematic set-up error for a cohort of patients with intracranial tumours treated with 3D Conformal Radiotherapy at the Department of Radiation Oncology, Groote Schuur Hospital, South Africa. After obtaining above mentioned data the ideal CTV-PTV expansion margin was calculated using published CTV-PTV expansion margin recipes. Patients and methods The Electronic Portal Images (EPID) of 20 patients who met the inclusion criteria were compared to their Digitally Reconstructed Radiograph (DRR). The set-up error for each patient was measured after which the random (s) and systematic (S) set-up error for the study group could be calculated. With both these values known the CTV-PTV expansion margin could be determined. Results The largest error was in the Superior/Inferior (SI) direction, followed by the Medial/Lateral (ML) direction and least in the Anterior/Posterior (AP) direction with 87.7%, 76.2% and 91.6% of the errors in the ML, SI and AP directions respectively being less than 3mm. There was no error larger than 5mm in the ML or AP direction with 6.1% of the SI error larger than 5mm. The random and systematic error in all three directions for this patient cohort were less than 2mm conforming to acceptable standards of delivering safe radiotherapy. Using Stroom's margin recipe (2S + 0.7s) a CTV-PTV expansion margin of 5mm can safely be applied for this patient cohort. Conclusion When treating patients with intracranial tumours at Groote Schuur Hospital the CTV-PTV expansion margin can safely be reduced from 1cm to 5mm.

Respiratory motion poses significant problems in the radiotherapy of tumors located at sites (lung, liver, pancreas, breast) that are affected by such motion. Effects of respiratory motion on the different stages of the radiotherapy process (imaging, treatment planning and treatment delivery), has formed the focus of significant research over the last decade. Results from such research have revealed that respiratory motion affects the instantaneous position of almost all structures in the thorax and abdomen to different degrees based on their corresponding anatomic location and muscular attachments. As an example, diaphragm motion was found to be of the order of 1.5 cm, predominantly in the superior-inferior (SI) direction during normal breathing. This indicates a similar magnitude of motion for tumors located in the lower lobes of the lung and in the abdomen.The conventional method of accounting for such motion is to add a margin (based on an estimate of the expected range of organ motion) around the clinical target volume (CTV) that is delineated from the image data. This margin also includes errors due beam-bony anatomy alignment during radiation delivery and errors in patient position between simulation and subsequent treatment delivery sessions. Such a margin estimate may or may not encompass the "current" extent of motion exhibited by the tumor, resulting in either a higher dose to the surrounding normal tissue or a potential cold spot in the tumor volume. Several clinical studies have reported the existence of a direct relationship between the reduction in mean dose to the lung and the incidence of radiation induced pneumonitis. Therefore, subjecting additional normal lung tissue to high dose radiation by adding large margins based on organ motion estimates may result in an increased risk of radiation induced lung injury.Monitoring and accounting for respiratory motion can however potentate a reduction in the amount of normal tissue that receives high dose radiation, thereby decreasing the probability of normal tissue complication and also increasing the possibility for dose escalation to the actual tumor volume. The management (monitoring and accounting) of respiratory motion during radiation oncology forms the primary theme of this dissertation.Specific aims of this thesis dissertation include (a) identifying the deleterious effects of respiratory motion on conventional radiation therapy techniques (b) examining the different solutions that have been proposed to counter the deleterious effects of respiratory motion during radiotherapy (c) summarizing the relevant work conducted at our institution as part of this thesis in addressing the issue of respiratory motion and (d) visualizing the future direction of research in the management of respiratory motion in radiation oncology.Among the various techniques available to manage respiratory motion in radiation oncology such as respiratory gated and breath hold based radiotherapy, our research initially focused on respiratory gated radiotherapy, employing a commercially available external marker based real time position monitoring system. Multiple session recordings of simultaneous diaphragm motion and external marker motion revealed a consistent linear relationship between the two signals indicating that the external marker motion (along the anterior-posterior (AP) direction) could be used as a "surrogate" for motion of internal anatomy (along the SI direction). The predictability of diaphragm motion based on such external marker motion both within and between treatment sessions was also determined to be of the order of 0.1 cm.Analysis of the parameters that affected the accuracy and efficacy of respiratory gated radiotherapy revealed a direct relationship between the amount of residual motion and the width of the "gate" window. It also followed therefore that a trade-off existed between the width of the "gate" and the accuracy of gated treatments and also the overall "Beam ON" time. Further, gating during exhale was found to be more reproducible than gating during inhale. Although, it was evident that a reduction in the width of the "gate" implied a reduction in the margins added around the clinical target volume (CTV), such a reduction was limited by setup error.A study of the potential gains that could be derived from respiratory gating (based on motion phantom experimental set up) indicated a potential CTV-PTV margin reduction of 0.2-1.1 cm while employing gating alone in combination with an electronic portal imaging device, thus decreasing the amount of healthy tissue receiving radiation. In addition, gating also improved the quality of images obtained during simulation by reducing the amount of motion artifacts that are typically seen during conventional spiral CT imaging.Imparting some form of training was hypothesized to better enable patients to breathe in a reproducible fashion, which was further thought to increase the accuracy and efficacy of gated radiotherapy, especially when the "gate" was set close to the inhale portion of the breathing cycle. An analysis of breathing patterns recorded from five patients over several sessions under conditions of normal quiet breathing, breathing with audio instructions and breathing with visual feedback indicated that training improved the reproducibility of amplitude or frequency of patient breathing cycles.An initial exploration into respiration synchronized radiotherapy was thought to facilitate realization of reduced margins without having to hold the radiation beam delivery during a breathing cycle (as is the case with gating). A feasibility study based on superimposition of respiratory motion of a tumor (simulated by a sinusoidal motion oscillator) onto the initial beam aperture as formed by the multileaf collimator (MLC) revealed that tumor dose measurements obtained with such a set up were equivalent to those delivered to a static tumor by a static beam.Finally, a feasibility study for a method to acquire respiration synchronized images of a motion phantom and a patient (in order to perform respiration synchronized treatment planning and delivery) yielded success in the form of a 4D CT data set with reduced motion artifacts.In summary, respiratory gated radiotherapy and respiration synchronized are both viable approaches to account for respiratory motion during radiotherapy. While respiratory gated radiotherapy has been successfully implemented in some centers, several technical advances are required to enable similar success in the implementation of respiration synchronized radiotherapy. However, the potential clinical gains that can be obtained from either of the above approaches and their relative contributions to margin reduction will determine their future applicability as routine treatment procedures.

The field of radiation oncology (RO) involves the use of highly advanced techniques to treat cancer and safely spare healthy organs. The discipline has experienced rapid growth in the past 25 years, with technological advancement as the driving force. Available data and an instrument to effectively measure the accessibility of innovation in the field were lacking. The purpose of this study was to investigate the accessibility of innovative services in RO in the United States and assess possible diffusion patterns. Two hundred and forty medical physicists practicing in RO in the United States completed a custom Internet-based survey. The diffusion of innovation theory was used as the theoretical framework for the study. A quantitative cross-sectional analysis was performed to assess how innovation scores may vary depending on individual and organizational factors. ANOVA, Spearman correlation, and multiple linear regression were used to analyze the data. University affiliation, urbanicity, appreciation, and motivation were found to be statistically significant factors affecting accessibility to innovative services. Statistically significant barriers preventing innovation were lack of evidence, increased complexity, staffing constraints, lack of interest from others, lack of interoperability, and lack of reimbursement. Medical physicists are in a leadership position to influence the adoption of innovative services in RO. Encouraging the utilization of innovative and Food and Drug Administration-approved techniques may improve cancer outcomes and consequently have a positive social change effect on public health.