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.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:502870 |
| Date | January 2009 |
| Creators | Land, Imke |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/2276/ |
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