ESTRO 2025 - Abstract Book

S2927

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

ESTRO 2025

4236

Digital Poster MORE ACCURATE TOTAL BODY IRRADIATION WITH IMPLEMENTATION OF NEW TECHNOLOGY Irene Rey López, Antonio A Alayón Afonso, Jorge F Obeso Fernández, Miguel Sánchez Carrascal, Celia Madán Rodriguez, Margarita P Melián Jiménez, Marta Lloret Sáez-Bravo Radiation Oncology, Hospital Universitario de Gran Canaria Dr Negrin, Las Palmas de Gran Canaria, Spain Purpose/Objective: Total body irradiation (TBI) has conventionally been performed with imprecise 3D-techniques. The aim of this study is to analyze if TBI using volumetric modulated arc therapy (VMAT) combined with image guidance with extended CBCT provides better accuracy, consistency, and resource optimization. Simulation CT is performed in our Department (Siemens Somatom Confidence multislice scanner). Two studies (5 mm slice thickness) per patient are done: first pelvis to head (upper), second pelvis to feet (lower), which are merged into a single study using Velocity software. Always taking the pelvis as the reference point. Dosimetry is performed with a multiple isocenter plan using the Eclipse planning system, conforming the dose distribution with VMAT. Patients received TBI in a Truebeam Linac Accelerator (SN3790, SN2137). Schedule: 2 Gy per fraction twice a day, with a 6-hour interval, up to 12 Gy total dose. Verification, positioning and treatment sessions are carried out first to the upper-part and then lower-one. Image guidance was conducted initially with KvMv images and then replaced by extended-CBCT which is fused with the simulation-CT to perform automatic adjustments. Parameters related with dosimetry and position verification are analyzed. Results: In this study a total of 136 treatment sessions to 25 patients were administered. All scheduled sessions were done. Median number of isocenters used were 6 (4-11). Lung mean dose was 10,54Gy (9,78Gy-11,22Gy). Dose homogeneity achieved across all sessions was 0.25 (0,11-0,36). Average dose rate was 2.85 cGy/min (2,06cGy/min-3,90cGy/min). Mean displacements after image acquisition were 0.08cm (0cm-2,0cm) laterally, 0.26cm (0cm-2,0cm) vertically, and 0.08cm (0cm-1,3cm) longitudinally. Average duration of each session, from patient's entry into the treatment room until their exit, was 89 minutes (47 275). Material/Methods: From November 2016 to December 2023, patients who were candidates for TBI were included. Simulation and treatment are performed in supine position.