Investigation of Volumetric Modulated Arc Therapy Dosimetry: from Planning to Delivery

Abstract

Volumetric modulated arc therapy (VMAT) for cancer treatment uses high-energy radiation to kill malignant cells. The general goal is to deliver a high and conformal dose to the target while minimizing dose to organs-at-risk. This thesis focuses on two areas in VMAT: developing high quality treatment plans and assessing the dosimetric impact of delivering pre-designed plans to patients whose anatomy and position change during treatment. Firstly, a quantitative assessment was made by comparing prostate plans optimized with and without a planning target volume upper dose constraint. It was found that removing the target dose uniformity requirement resulted in better rectum sparing and improved tumor control probability. Secondly, the impact of body contour changes on dose distributions for prostate and head and neck VMAT plans was examined. Rules of thumb for dose percentage change and isodose line shift were developed and body contour changes unlikely to require further investigations were addressed.