ESTRO 2025 - Abstract Book

S3318

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

ESTRO 2025

Results: A total of 98 proton fractions were analyzed. The median number of BHs per CBCT/fraction was 1 [1; 5], and per treatment/fraction was 5 [3; 18]. During beam-on, the median isocenter shift deviation remained within 3 mm for all patients and fractions, though shifts during CBCT were marginally higher for some patients attributable to the need of manually interrupting the CBCT (Fig.2). Fraction times went from 45 to 30 minutes as patients and technologists became more familiar with the process. The reCT dosimetric analysis was faster compared to the 4DCT workflow in free-breathing. No plan adaptations were required for any patient. Residual CTV shifts are being collected, and margins will be evaluated after treating the first 10 patients. Note that using increased number of beams, along with any challenges in maintaining breath-holds, could potentially lead to intra-fraction shifts.