ESTRO 2025 - Abstract Book

S4336

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

This study compares the performance of baseline, sequential, and robust treatment planning (BTP, STP, and RTP) by adjusting target margins and motion. Our objective is to reduce target margins while preserving adequate target coverage. Material/Methods: This study included nine high-risk prostate cancer patients, each with one planning CT and five cone-beam CTs (CBCTs). Nominal plans were evaluated on the planning CT, while simulated plans also used CBCTs to create six simulated dose fractions through deformable image registration and dose warping. All plans employed volumetric modulated arc therapy (VMAT), delivering a dose of 77 Gy to the prostate and 56 Gy to lymph nodes and seminal vesicles over 35 fractions. BTP involved delivering a simultaneous dose to all targets in a dual arc, using fiducial markers for simulation positioning. In STP, the lowest common dose level was delivered to all targets in a dual arc, serving as a base for an additional arc targeting the prostate. The patient was first positioned based on bone anatomy, then fiducial markers for simulations. RTP was designed to accommodate lymph node movement by delivering a simultaneous dose to all targets in a dual arc, using gold fiducial markers as simulation reference. Plan evaluation included clinical goal passing rates and a plan score based on normalized and weighted dose/volume metrics. Results: In clinical goal passing rates, the best nominal plans were the STPs with the smallest margins, specifically 3 5,3 and 3 5,5 passing 92.19% of clinical goals, while the worst was 5,7 , passing 77.37%. For simulated plans, the 4 5,7 showed the highest pass rate at 85.02%, and 5,7 the lowest at 76.68%.