S1842
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Humanitas Research Hospital IRCCS, Milan-Rozzano, Italy
Purpose/Objective: Heart irradiation during breast cancer radiotherapy has been widely studied over the last decade. Darby et al [1] correlated major coronary events with he mean heart dose in patients treated with two tangential beams. More recent studies have shown the need to evaluate heart sub-structure doses beyond the mean heart dose, especially with the increasing use of VMAT for breast treatments. This study evaluates the correlation of heart sub-structure doses between VMAT and tangential Field-in-Field techniques. Material/Methods: Ninety-two left-sided breast patients were replanned with both tangential Field-in-Field and VMAT techniques to deliver 50 Gy in 25 fractions, matching Darby’s fractionation for comparative analysis. Heart and sub-structure volumes were contoured using the TheraPanacea auto-contouring software. First, the correlation between mean heart dose and the heart Vx parameter was assessed for tangential fields, to link potential clinical outcomes from Darby’s findings. Subsequently, correlations between mean heart dose and specific sub-structures in tangential fields were investigated. Finally, doses to these sub-structures were compared between VMAT and tangential fields to identify the potentially less toxic technique for the same mean heart dose. Results: In the tangential field setting, the whole heart Vx parameters correlated well with the mean heart dose. The heart sub-structures receiving the highest dose were the LAD and the left ventricle. The sub-structure whose mean dose correlated best with the mean whole heart dose was the left ventricle. The following figure shows the correlation of V70% of the whole heart and the mean dose to the left ventricle relative to the mean heart dose.
The mean dose to the different substructures in the two techniques (tangential Field-in-Field and VMAT) showed a substantial reduction with VMAT, as shown in the following figure for LAD and the left ventricle:
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