ESTRO 2025 - Abstract Book

S2777

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

associated with higher NT volumes compared to electrons. Using the automated app, IMRT plans were completed in 52s ± 11s and 92 ± 9s.

Conclusion: The automated planning technology produces plans in less than two minutes that are superior in quality to electron plans in all aspects examined. This technology may prove useful in the adoption of O-ring treatment platforms in presenting an efficacious solution for skin cancer treatment.

Keywords: Skin, treatment planning, automation

References: [1] Yoesfof E, Kurman N, Yaniv D, The role of radiation therapy in the treatment of non-melanoma skin cancer, Cancers 2023 April 22; 15(9):2408. 1707 Digital Poster Robust optimisation to account for delineation uncertainty in recurrent gynaecological cancer Sooha Kim 1,2 , Hoda Abdel-Aty 1 , Arvind Sathyamurthy 1 , David Bernstein 3,4 , Alexandra Taylor 1,2 1 Gynaecology Unit, The Royal Marsden NHS Foundation Trust, London, United Kingdom. 2 Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom. 3 Joint department of Physics, The Royal Marsden NHS Foundation Trust, London, United Kingdom. 4 Joint department of Physics, The Institute of Cancer Research, London, United Kingdom Purpose/Objective: Delineation uncertainty (DU) is considered to be the largest systematic error in modern radiotherapy (1) . The traditional PTV approach is not well suited to account for DU, risking suboptimal target coverage and OAR sparing. This study presents a novel and practical framework for robust optimisation that integrates DU directly into treatment planning, providing a more personalised solution compared to the PTV approach. Material/Methods: A methodology for robust optimisation (RO) incorporating DU was developed and tested in a phantom study. This was applied to recurrent pelvic gynaecological cancer, where DU is significant. 10 experienced clinical oncologists and radiologists contoured CTVs and OARs (rectum, sigmoid, bladder and bowel) across 10 cases using MR-CT fusion. The CTV was prescribed 20Gy in 5 fractions with SBRT, as a boost following 45Gy in 25 fractions to the pelvis. The traditional PTV plan used a reference CTV, expanded isotropically by a margin calculated based on the Van Herk formula, with delineation error measured across all cases. Plans were generated in Eclipse TPS with planning aims of PTV D95%> 20Gy, PTV Dmax between 24 – 28Gy (120 – 140% of prescribed dose) and a reference CTV D95% >22Gy (110%) for central dose escalation. OAR constraints followed EMBRACE II mandatory constraints (D2cc < 75Gy