"Sequential Volumetric Modulated Arc Therapy (VMAT) Boost in Hy- brid Plan With Tangential Beams for Whole Breast Treatment: a Do- simetric Study "

"Purpose: Whole breast radiation therapy (WBRT) with a boost to the tumor bed following con-servative primary surgery in women with breast cancer (BC) plays a central role in reducing local recurrences and mortality. Volumetric modulated arc therapy (VMAT) technique has been shown to allow better dose conformation with low dose levels to organs at risk (OARs), compared to static fields three-dimensional Conformal Radiotherapy (3D-CRT). The aim of this study was to evaluate the feasibility and dosimetric advantages of sequential boost (SB), administered with VMAT tech-nique in hybrid plans with tangential beams for whole breast treatment. Material and methods: BC patients undergoing adjuvant RT from June to October 2020 were selected. ESTRO guidelines for the Clinical Target Volume (CTV) delineation were used. Total delivered dose was 60-66 Gy; 50 Gy in 2 Gy daily fractions for whole breast and 10-16 in 2 Gy daily fractions Gy to tumor bed was 10-16 Gy in 2 Gy daily fractions. Results: The analysis included 31 patients with BC treated with adjuvant RT following con-servative surgery. Hybrid treatment plans characterized by a 3D-CRT plan using tangential medi-olateral and lateromedial fields for the irradiation of the whole breast Planning Target Volume (PTV) and a sequential VMAT plan with 2 coplanar arches for boost PTV irradiation were gener-ated. Dosimetric analysis resulted in homogeneous target volumes coverage and OARs constraints compliance. As regarding to organs at risks (OARs), contralateral breast, ipsi- and contralateral lung and heart constraints values were analysed. Conclusions: In the frame BC RT, this dosimetric study showed that hybrid plans performed with 3D-CRT and VMAT techniques are feasible in terms of dosimetric outcomes. "