ESTRO 2025 - Abstract Book

S3324

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

ESTRO 2025

Results: In total, 99 fractions were available for the CBCT1-CBCT2 registration and 92 fractions for the CBCT2-CBCT3. For CBCT1-CBCT2, the largest median shift was 2.2 mm in the Anterior-Posterior (AP) direction (Table 1). The median vector displacement was 3.0 mm, with a maximum excursion of 8.4 mm. For CBCT2-CBCT3, the measured shifts were statistically significantly lower for all directions (p<0.001), with a median vector displacement of 1.2 mm.

Conclusion: In this study we measured intrafraction displacements of the breast during an oART workflow for right-sided whole breast irradiation. Our results indicate that displacements were larger during the treatment planning phase (CBCT1 CBCT2) than during radiotherapy delivery (CBCT2-CBCT3). The 5 mm PTV margin was sufficient to account for intrafraction motion in 20 patients, but further study is needed to determine if the current margin could be reduced.

Keywords: online adaptive, breast, intrafraction

References: 1. Nelissen K.J. et al: Clinical implementation of Cone-beam CT guided online adaptive radiotherapy in whole breast irradiation. Advances in Radiation Oncology. 2024 Nov 5:101664.