ESTRO 2025 - Abstract Book

S3330

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

ESTRO 2025

CTV coverage, as illustrated in Figure 1 . The proposed margins were compared with conventional 5 mm isotropic margins, both geometrically and dosimetrically. In the geometrical comparison, doses to organs at risk (OAR), PTV volumes, and CTV coverages with different margins were assessed. For the dosimetric comparison, the sixth to the tenth fractions of each patient were re-treated on emulators using different margins, and the doses deposited in the pseudo-CT (sCT) were compared.

Results: The personalized anisotropic margins led to a 13% reduction in PTV volume compared to the 5 mm isotropic margins. The doses to critical OARs, including the small intestines, bladders, and rectums, were significantly decreased, as shown in Figure 2. In the geometric evaluation, the CTV geometric coverage was maintained at 99.23 ± 0.64%. In the dosimetric evaluation, the prescription dose coverage was maintained at 98.3 ± 1.5% with the proposed anisotropic margin strategy, validating the safety of the reduced PTV volumes.