ESTRO 2025 - Abstract Book

S2020

Clinical - Urology

ESTRO 2025

2916

Digital Poster Automatic Beam Hold (ABH) Linac-Integrated Motion Control System in Hypofractionated Prostate Radiotherapy: Initial Findings and Clinical Implication. Simone Baroni 1 , Nicola Padula 2,3 , Claudio Scaffidi 1,4 , Luca Frassinelli 1 , Rachele Petrucci 1 , Anna Sardo 2 , Marco Lucci Chiarissi 5 , Claudia Ganga 5 , Francesco Varvello 5 , Francesco Lucio 2 , Alessia Reali 1 1 SSD Radioterapia, Ospedale Michele e Pietro Ferrero-Aslcn2, Verduno, Italy. 2 SSD Fisica Sanitaria, Ospedale Michele e Pietro Ferrero-Aslcn2, Verduno, Italy. 3 SSC Fisica Sanitaria, Università degli Studi di Torino, Torino, Italy. 4 SSC Radioterapia, Università degli Studi di Genova, Genova, Italy. 5 SOC Urologia, Ospedale Michele e Pietro Ferrero Aslcn2, Verduno, Italy Purpose/Objective: The use of hypofractionated radiotherapy and SBRT for prostate cancer is becoming more and more common. Prostate motion during treatment may result in dose discrepancies therefore it is critical to control intrafractional motion, particularly when higher doses per fraction are employed. This work presents our initial single center experience of a linac-integrated intra-fraction motion control system based on gold fiducials and kV imaging, concurrent with ABH in hypofractionated prostate radiotherapy. Material/Methods: Since 2022, prostate cancer patients receiving hypofractionated radiotherapy with a dose per fraction of 3 Gy or more underwent 3 fiducial implants performed by an urologist. 2 weeks later, a simulation Computed Tomography (CT) scan is completed with rectal and bladder preparation. A volumetric modulated arc therapy (VMAT) plan was developed for all patients using a flattening filter-free (FFF) delivery technique. The position of the gold fiducials is monitored during each fraction using integrated 2-Dimensional kV-imaging in the Varian Truebeam® linac with the ABH feature. In the event of a fiducial moving beyond a spherical threshold of 4 mm radius, the photon beam is automatically halted. 2-D kV imagines was acquired every 5 seconds or every 20° degrees as clinician choice. If necessary, reimaging (2D kV-images or ConeBeam-CT) for re-engagement or patient repositioning would be required. Acute toxicity was reported in accordance with the to common Terminology Criteria for Adverse Events version 5.0 (CTCAE). Results: 11 patients with implanted fiducials were treated, 7 underwent sbrt at 36.25 Gy/5fr and 4 received hypofractionated treatment at 60 Gy/20 fr. No fiducial implant complications were observed. A total of 115 treatment fractions were analyzed. 2589 2D kV-images were acquired and ABH interruptions occurred in 210 (8,1%) of cases due to fiducial movement out of threshold. In the SBRT subgroup, there were 1281 images and 148 treatment halts (11,5%). Repeat 2D imaging for fiducial re-engagement was needed 35 times. 3 instances required patient repositioning. Average session time was 18’ and 20’’, longer than conventional prostate radiotherapy session time. No acute GU or GE toxicity> G1 was observed. Conclusion: Hypofractionated treatment with intrafraction motion monitoring for prostate cancer is feasible using ABH linac integrated system. The ABH system was involved in over 10% of cases, particularly in stereotactic sessions, as evidenced in the literature. The increase in session time is balanced by a reduction in the number of fractions. It is essential to collate the data on late toxicities.

Keywords: intrafraction motion management prostate sbrt