ESTRO 2025 - Abstract Book

S3246

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

timeframe for a >3mm prostate shift in any direction over all analyzed fractions was 3.0 minutes. The same time was 7.3 minutes for >5mm shifts.

Conclusion: Intrafraction monitoring with TPUS was feasible and effective. It was well confirmed that prostate motion increases with time. Our fast treatment time helped minimize the number of interruptions needed, although in some cases, unexpected prostate motion still occurred. This underscores the importance of using real-time monitoring devices when applying 3mm margins.

Keywords: prostate SBRT, intrafraction motion, ultrasound

2169

Proffered Paper First clinical application of Comprehensive Motion Management with 1.5T MR-linac on prostate cancer patients treated with radiotherapy Luca Nicosia 1 , Michele Rigo 1 , Roberto G Pellegrini 2 , Patel Nishant 2 , Andrea Gaetano Allegra 1 , Nicola Bianchi 1 , Riccardo Filippo Borgese 1 , Chiara De-Colle 1 , Antonio De Simone 1 , Niccolò Giaj-Levra 1 , Davide Gurrera 1 , Stefania Naccarato 1 , Edoardo Pastorello 1 , Francesco Ricchetti 1 , Gianluisa Sicignano 1 , Ruggiero Ruggeri 1 , Filippo Alongi 1 1 Department of Advanced Radiation Oncology, IRCCS Sacro Cuore Don Calabria, Negrar di Valpolicella, Italy. 2 Medical Affairs, Elekta AB, Stockholm, Sweden Purpose/Objective: MR-guided radiotherapy (MRgRT) on MR-linac (MRL) with daily online plan adaptation permits to control interfraction variability. Recently, Comprehensive Motion Management (CMM) is a tool for 1.5T MRL that interrupt dose delivery when the target moves outside the defined position and permits target drift corrections compensating for intrafraction variability. We report the first clinical experience on prostate adaptive radiotherapy (RT) on 1.5T MRL with the use of CMM. Material/Methods: 60 patients affected by low-to-intermediate risk prostate cancer were treated with CMM at the 1.5T MRL. PTV margins were 5 mm in all directions and 3 mm posteriorly. Fifty patients were treated with stereotactic RT (SBRT), while 10 patients with hypofractionated RT (hypoRT). CMM threshold was set to 100% of the GTV volume. Results: 450 treatment fractions were administered. Median beam-on time of 10.3 minutes and a median duty cycle of 98.9% (95%CI 98.6-99.2%). Beam-hold occurred in 158 fractions (35%), for a mean beam-hold count of 24.5 instances (95%CI 16-32). Thirty-two baseline shift replanning were performed. Acute toxicity consisted in cystitis grade (G) 1 in 10 cases (17.5%), G2 in 2 cases (3.5%), proctitis G1 in 6 cases (10.5%) and G2 in 2 cases (3.5%). No G3 or higher toxicity occurred. Conclusion: CMM has been successfully implemented on 1.5T MRL. Because the process is completely automated, included cases of in-treatment corrections and baseline shift replanning, the treatment time remains limited, without affecting patient’s compliance and treatment feasibility. CMM could potentially allow for a safe reduction of the PTV margins.

Keywords: prostate cancer, MRgRT, CMM