ESTRO 2025 - Abstract Book

S4387

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

tissues. This approach minimizes the side effects of radiation therapy and enhances therapeutic efficacy, making it beneficial for patients undergoing hypofractionated radiation therapy for prostate cancer.

Keywords: Prostate cancer, Hypofractionated RT, SpaceOAR

References: M. Fagundes, 2021, Expanding the Utilization, advances oncol, DOI:10.1016/j.adro.2021.100651 A.C. Tree, 2013, Biological Dose Escalation, clinical oncol, DOI:10.1016/j.clon.2013.05.003 Pinkawa, 2014, Spacer application for, future oncol, DOI:10.2217/fon.13.223 Zelefsky, 2020, Early Tolerance and, eur urol oncol, DOI: 10.1016/j.euo.2019.09.006. Paetkau, 2019, Maximizing rectal dose, J Appl Clin Med Phys, DOI :10.1002/acm2.12566 P. Sturt, 2022, The dosimetric advantages, meddos, DOI: 10.1016/j.meddos.2022.02.003 A. Widmark, 2019, Ultra-hypofractionated, DOI:10.1016 Mariados, 2015, Hydrogel Spacer Prospective, redjon, DOI:10.1016/j.ijrobp.2015.04.030 Nakamura, 2001, Dose conformity of, Radiation Oncology Biol, DOI:10.1016/s0360-3016(01)01757-6

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Digital Poster Analysis and comparison of CyberKnife MLC collimator versus IRIS collimator in prostate SBRT Gaetano Gagliardo 1 , Marcello Serra 2 , Gianluca Ametrano 2 , Valentina d'Alesio 2 , Francesca Buonanno 2 , Cecilia Arrichiello 2 , Rossella Di Franco 2 , Valentina Borzillo 2 , Esmeralda Scipilliti 2 , Rocco Mottareale 1 , Mariagabriella Pugliese 3 , Maria Quarto 1 , Paolo Muto 2 1 Advanced Biomedical Science Department, University of Naples Federico II, Naples, Italy. 2 Department of Radiation Oncology, Istituto Nazionale Tumori-IRCCS-Fondazione G. Pascale, Naples, Italy. 3 Department of Physics “E. Pancini”, University of Naples Federico II, Naples, Italy Purpose/Objective: CyberKnife (CK) is a key technique for treating localized prostate cancer with hypofractionated radiotherapy. This study aims to compare the radiation dose and treatment efficiency of CK using multileaf collimator (MLC) versus IRIS collimator for prostate SBRT, focusing on dose distribution, organ-at-risk sparing, beam-on time and monitor units. Material/Methods: Treatment plans were generated for 11 prostate cancer patients treated with CK at the Istituto Nazionale Tumori - IRCCS Fondazione G. Pascale in 2024. For each patient, two distinct treatment plans were developed: one using the IRIS collimator and the other one employing MLC collimator. To enable a consistent dosimetric comparison, each treatment plan was designed to ensure identical PTV coverage for each patient when using the two different collimators. For all patients, PTV coverage was maintained between 95% and 100%. Results: Dose values and study parameters were averaged across plans for each collimator. A Student's t-test was used to compare the mean values between the two techniques. Results show a significant reduction in treatment time (31%) with the MLC collimator (27 min vs. 40 min for IRIS, ρ=0.000003). Monitor units also decrease by 51% with MLC, averaging 24,364 per treatment compared to 49,890 for IRIS (ρ=0.000002). Table 1 summarizes the mean values for the main dosimetric parameters under study: CI, nCI, HI, and GI.