Half-Field Segmented VMAT Spares Organs at Risk from Postoperative Left Breast Cancer Radiotherapy

Abstract

<h3>Purpose/Objective(s)</h3> To investigate the efficacy and applicability of the half-field segmented volumetric modulated arc therapy (VMAT) in postoperative left breast cancer radiotherapy. <h3>Materials/Methods</h3> The dosimetric characteristics of 6 MV 12 × 16 cm2 full field and jaw blocked half field were studied using a water phantom. Half-field segmented VMAT plans were designed for 20 left breast cancer patients. These patients underwent conventional full-field VMAT postoperative radiotherapy and received a prescription dose of 50 Gy in 25 fractions. Dosimetric parameters and treatment efficiency for the target volume and the organs at risk were compared between the two techniques. Furthermore, the planned dose distributions were assessed using the ideal dose predicted by PlanIQ. <h3>Results</h3> Compared with the full-field VMAT, the half-field segmented VMAT plan significantly reduced V5, V30, and Dmean of the affected lung, the heart, and the cardiac substructures, as well as V20 of the affected lung (P < 0.05). The dosimetric metrics for the target volume and the planned monitor units (MUs) were similar in both settings (P > 0.05), with the half-field segmented VMAT plan having fewer MUs. Except for the right lung, other organs at risk achieved the ideal dose in the half-field segmented VMAT plan, with significantly lower doses in V30 of the heart and Dmean of the left ventricle than those of the predicted ideal dose (P < 0.05). <h3>Conclusion</h3> The half-field segmented VMAT achieved better dose conformality to the target volume and better protected the heart and the left lung for left breast cancer patients.