Modeling of radiation dose deposition in time-varying geometries

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The aim of radiation therapy is to deliver a high dose of ionizing radiation to destroy malignant tumor cells while sparing the surrounding healthy tissue to avoid treatment-related side effects. Traditionally, radiation therapy treatment planning has assumed that the patient's geometry remains static during the treatment delivery. However, it is known that the internal anatomy undergoes significant motion and deformation due to respiratory motion which can result in blurring and distortion of the delivered dose distribution. Recent advances in radiation therapy have focused on methods to measure and correct for respiration-induced anatomical changes. Quantification of the impact of respiratory motion and the development of new treatment planning methods requires dose calculation methods to estimate the radiation dose deposited in the time-varying (4D) geometry. These 4D dose calculation methods rely on deformable image registration, a method for determining the geometric transformation between a series of images, to obtain a model of the motion between anatomical states. The use of deformable image registration and 4D dose calculation introduce additional complexities into the treatment planning process and potential innaccuracies must be carefully evaluated. This research aims to investigate how uncertainties in image registration affect the accuracy of 4D dose calculation. We will also perform a comprehensive evaluation of 4D dose calculation methods for photon and proton radiotherapy to quantify the uncertainty introduced by the dose calculation method. The aim of this research is to understand how the uncertainties in the image registration and dose calculation limit the achievable accuracy of sophisticated 4D treatment planning techniques and to develop new robust algorithms which can safely deliver the intended radiation treatment to moving tumours.