Performance and Effect of Automatic Contouring in Automatic Adaptive Planning for Prostate Cancer Volumetric Modulated Radiotherapy

Volumetric modulated radiotherapy (VMAT) has been widely used in treating prostate cancer. However, when large daily inter-fractional anatomic changes occur, a simple iso-center shift may not be adequate for target coverage and normal tissue sparing. The fully adaptive radiotherapy involves re-planning process based on daily repeat computed tomography images (CTs), which is impractical with the manual re-contouring and trial-and-error re-planning process. In this paper, we quantitatively evaluated the performance of automatic contouring in an automatic adaptive planning method on cone beam CTs, and demonstrated the feasibility and effectiveness of using the auto contours for online automatic adaptive planning to compensate for the target dose deficit and the critical organ overdose caused by inter-fractional anatomical changes for prostate cancer. Keywords: Adaptive radiotherapy, automatic contouring, automatic re-planning, deformable image registration, inter-fractional motion, prostate cancer, volumetric modulated radiotherapy.