Mitigating daily organ motion in pelvic radiotherapy

Accurate delivery of external beam radiotherapy in the pelvis is challenged by substantial anatomical changes induced by daily organ motion. Consequently, large treatment margins are typically required to ensure adequate dosing of the target volume. However, this target volume expansion also means that more dose is deposited in healthy tissue, potentially resulting in higher toxicities. Therefore, adaptive strategies have been devised that increase the conformity of the treatment, by acting on observed changes in the human anatomy. One such adaptive strategy is the ‘Library of Plans’ (LoP) method, in which multiple treatment plans are made prior to the start of treatment. At each daily fraction, the most suitable treatment plan is then selected based on a pretreatment scan revealing the anatomy of the day.
The main objective of this thesis was to develop methodologies to improve such online adaptive strategies for pelvic radiotherapy, thereby increasing treatment conformity. Specifically, population based and personalized library of plans strategies were developed for rectal and cervical cancer, respectively. Furthermore, to aid plan selection, a method to automatically segment the target volume on the daily acquired scans was proposed.