Abstract
Volumetric modulated arc therapy (VMAT) has been implemented for left breast irradiation to reduce prescription dose to the heart and improve dose homogeneity across the targeted breast. Our in‐house method requires application of a bolus during the optimization process with a target outside of the body, then removing the bolus during the final calculation in order to incorporate skin flash in VMAT plans. To quantify the dosimetric trade‐offs between traditional 3D field‐in‐field tangents and VMAT with integrated skin flash for these patients, we compared nine consecutive patients who recently received radiation to their entire left breast but not their regional lymphatics. Tangent plans used non‐divergent tangents of mixed energies and VMAT plans utilized four 6 MV arcs of roughly 260°. Mean dose to the heart, contralateral lung, and contralateral breast and their volume receiving 5%, 10%, and 20% of the prescription dose were higher in all nine VMAT plans than in the static tangential beam plans. For all critical structures, the mean VMAT DVH was higher in the low‐dose region and crossed the 3D field‐in‐field DVH between 23.13% and 34.18% of the prescription dose (984.75‐1454.70 cGy). However, the volume of the contralateral breast and heart receiving the prescription dose was slightly lower in the VMAT plans, but not statistically significant. VMAT provided superior homogeneity, with a mean homogeneity index of 9.41 ± 1.64 compared to 11.05 ± 1.82 for 3D tangents. Results indicate that VMAT spares the heart, contralateral lung, and contralateral breast from prescription dose at the cost of increasing their mean and low‐dose volume and delivers a more homogenous dose distribution to the breast. For these reasons, VMAT is selectively applied at the request of the physician for left breast radiation without respiratory gating to spare the heart from prescription dose in cases of poor anatomical geometry.
Highlights
The application of Volumetric modulated arc therapy (VMAT) to left breast irradiation has raised concern about potential cardiac toxicity
The volume of the contralateral breast and heart receiving the prescription dose was slightly lower in the VMAT plans, but not statistically significant
Left panel is a volumetric modulated arc therapy plan optimized to meet the constraints set by the physician, and the right panel is a three‐dimensional field‐in‐field plan with tangents placed to encompass the left breast while maximizing sparing of the ipsilateral lung, heart, and contralateral breast
Summary
The application of VMAT to left breast irradiation has raised concern about potential cardiac toxicity. Respiratory gating techniques such as voluntary deep inspiration breath‐hold (DIBH), which has been shown to protect the heart by displacing it from the chest wall, are not available at many institutions.[1,2]. VMAT and intensity‐modulated radiotherapy (IMRT) with built‐in skin flash may decrease the heart dose but increase low‐dose exposure of nearby healthy tissues compared with three‐dimensional (3D) field‐in‐field tangents.[3–9]. This study quantifies the dosimetric trade‐offs and crossover points between low‐ and high‐dose volumes for left breast cancer patients treated with the VMAT with the integrated skin flash planning method compared to results obtained using conventional 3D planning techniques
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