ESTRO 2025 - Abstract Book

S4070

RTT - Patient care, preparation, immobilisation and IGRT verification protocols

ESTRO 2025

The greatest variation observed was in the in the pitch (X) and yaw (Z) planes which were inside institutional tolerance throughout the treatment course.

Conclusion: With greater imaging capabilities and daily adaptations, the MRL could compensate for increased movement in the open faced mask. However, wearing no immobilisation device is not feasible for H&N RT.

Keywords: Open faced mask

References: 1. Lastrucci A, Morelli I, Votta C, Maran I, Iosca N, Monaco IP, Salvestrini V, Desideri I, Marrazzo L, Wandael Y, Cornacchione P. Open-Face Masks in Radiotherapy: Enhancing Therapeutic Strategies for Head and Neck and Brain Cancer Patients—A Comprehensive Scoping Review. Cancers. 2024 Aug 21;16(16):2899.

1848

Poster Discussion Rectal preparation for prostate cancer IGRT: help or hassle? Sophie E Alexander 1,2 , Lucy Booth 3 , Louise Delacroix 3 , Emma Garrad 1 , Alexandra Gordon 3 , Adriana Guerra 1 , Hosna Mohammad 1 , Simeon Nill 4 , Clare Ockwell 1 , Uwe Oelfke 4 , Helen A McNair 1,2 , Alison C Tree 3,2 1 Radiotherapy, The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom. 2 Radiotherapy and Imaging, The Institute of Cancer Research, Sutton, United Kingdom. 3 Uro-Oncology, The Royal Marsden NHS Foundation Trust, Sutton, United Kingdom. 4 Joint Department of Physics, The Royal Marsden Hospital and the Institute of Cancer Research, Sutton, United Kingdom Purpose/Objective: To evaluate the impact of stopping rectal preparation for patients undergoing radiotherapy (RT) for localised prostate cancer (PCa), with respect to inter and intrafraction motion and rectal volume stability. Material/Methods: Forty patients with localised PCa, receiving RT May-September 2024, were retrospectively evaluated. Eligible individuals had: • No rectal preparation (bladder filling advised) • Prostate RT, 60Gy/20-fractions, c-arm linac, VMAT • Daily CBCT-guidance, dual registration to bone then implanted fiducials or prostate soft-tissue, following an online no action level protocol • Post-treatment CBCT fractions 1, 5, 10, 15 and 20 All CBCT images were matched online by two therapeutic radiographers. Isocentre deviations for bone and fiducial/soft-tissue registrations were exported from Mosaiq (Elekta, Sweden) to Excel (Microsoft, USA). Interfraction independent prostate motion was calculated by subtracting bone registration from fiducial/soft-tissue registration values. Total Intrafraction motion was the difference in fiducial/soft-tissue displacements between pre- and post-treatment CBCT on fractions 1, 5, 10, 15 and 20. Independent prostate motion was calculated by subtracting bone registration values from fiducial/soft-tissue displacements. Rectal volume was contoured on the planning CT and pre-/post-treatment CBCT for fractions 1, 5, 10, 15, and 20 (RayStation, RaySearch, Sweden). Findings were compared to 20 preceding patients, matched by RT prescription and delivery protocol, who used micro-enema rectal preparation for planning CT and the first 10-fractions of RT.

Results: