ESTRO 2025 - Abstract Book

S1985

Clinical - Urology

ESTRO 2025

2143

Digital Poster Is it possible to avoid using a rectal balloon for prostate treatment with highly hypofractionated proton therapy? Nikita Kataev 1 , Andrey Luybinskiy 2 , Nikolay Vorobyov 1,3 , Marina Linnik 1 , Nataliia Martynova 1 , Georgiy Andreev 2 , Yulia Gutsalo 1 , Natalia Berezina 4 , Kirill Suprun 5,6 1 Proton Therapy, MIBS, Saint Petersburg, Russian Federation. 2 Medical Physics, MIBS, Saint Petersburg, Russian Federation. 3 Oncology, SPbU, Saint Petersburg, Russian Federation. 4 Administrative, MIBS, Saint Petersburg, Russian Federation. 5 Surgery, MIBS, Saint Petersburg, Russian Federation. 6 Surgery, SPbU, Saint Petersburg, Russian Federation Purpose/Objective: It is well known that irradiation with large fractions requires either high-precision intrafraction control or fixation of the target, but in the conditions of a high-flow center a fast and reliable method is required, which for us was the use of an endorectal balloon for prostate treatment. In our practice some patients were not satisfied with the experience of using this device and for proton therapy the peculiarities of dose distribution do not allow to get ideal dose loads with the balloon on the rectum. We wanted to investigate whether omitting usage of endorectal balloon possible for ultrahypofraction. The aim of our study is to find out to what extent the cancellation of balloon use may affect the feasibility of treatment and to what extent we will be limited in treatment by the shift of the target within robustness. Material/Methods: We analyzed 23 courses with total of 149 CBCT with average 1.3 CBCT per fraction (range 1-5). All patients were treated in five fractions with total dose 36.25 Gy for prostate and seminal vessels. For all patients were used institutional protocol of simulation and treatment preparation for rectum and bladder. Also, according to our protocol, we canceled treatment in case of unsatisfactory preparation for treatment and/or due to a shift intreatment volume. We analyzed treatment volume position shifts, and it effect on successful fraction performance and determined other reasons of treatment cancelation. Results: Margins necessary to encompass prostate treatment volume D100% for patients in lateral, cranio/caudal, and anterior/posterior dimensions were maximally 6,8 and 8mm, respectively. Angles were 9.9,8/1 and 1.9 degree. Average motions of treatment volume were in the lateral, cranio/caudal, and anterior/posterior dimensions would be 0.3,0.4 and 0.2mm, respectively. Angles were 0.45,0.04 and 0.02degree. All variations are shown below