ESTRO 2025 - Abstract Book

S2814

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

according to a breathing trace with lateral, longitudinal, and vertical amplitudes of 2.6 mm, 3.8 mm, and 5.3 mm respectively 4 . Dose-volume metrics were used to quantify plan degradation to the whole breast and IMC planning target volumes (PTV WB and PTV IMC ), ipsilateral lung and the heart. Results: Tables 1 and 2 show results for the right-sided and left-sided patients, respectively. When accounting for breathing induced interplay, the WT plans PTV WB D95 went from nominal median dose of 2532 cGy to 2531 cGy, VMAT PTV WB D95 went from nominal 3808 cGy to 3788 cGy. The median value of D95 PTV IMC degraded from 3124 cGy to 2904 cGy for WT plans and from 3789 cGy to 3741 cGy for VMAT plans. The median mean heart dose from the WT plans increased by 8 cGy with the simulated motion, whereas the VMAT increased by 5 cGy. The median ipsilateral lung mean dose for WT plans decreased by 7 cGy and increased by 1 cGy for VMAT plans, when the interplay effect was included.

Conclusion: In this study, the degree of plan degradation in free breathing conditions has been shown to be similar for WT and VMAT breast and nodal irradiation plans. Although breath-hold is a preferred technique to improve heart-sparing, this study has shown that VMAT breast and nodal irradiation in free breathing is a feasible technique for patients who cannot tolerate breath hold.

Keywords: Free-Breathing, VMAT