Abstract
BACKGROUND: Adjuvant radiotherapy after breast-conserving surgery reduces local recurrence and improves survival in breast cancer. For left-sided tumors, achieving homogeneous target coverage while minimizing dose to organs at risk (OARs), particularly the heart and ipsilateral lung, remains challenging. The German S3-Guideline recommends hypofractionated whole-breast irradiation combined with deep inspiration breath hold (DIBH) to limit heart dose. This planning study compared conventional 3D conformal tangential radiotherapy (3D-FiF) and continuous-arc VMAT (cVMAT) with a novel tangential partial-arc VMAT technique (tVMAT) in left-sided breast cancer. METHODS: Twenty patients with left-sided breast cancer were included. For each patient, three DIBH treatment plans were generated: 3D-FiF with two opposed tangential fields and two subfields, cVMAT with a 240° double arc, and tVMAT with two partial double arcs of 40° each. Dose differences were evaluated using the Wilcoxon signed-rank test. RESULTS: Dose coverage of the clinical target volume (CTV) (D(95%)) was comparable between 3D-FiF and tVMAT, while cVMAT required a higher dose. tVMAT achieved a more homogeneous CTV dose distribution and showed significantly better conformity for both planning target volume (PTV) and CTV compared to 3D-FiF. Compared to cVMAT, tVMAT provided similar conformity and homogeneity for the PTV but lower mean doses to the heart, LAD, and left ventricle. 3D-FiF resulted in the lowest low-dose exposure of the lungs and contralateral breast, while tVMAT reduced these doses by factor 2.06 for the contralateral breast and factor 2.38 for the contralateral lung. CONCLUSIONS: tVMAT proved to be a robust and reproducible irradiation technique for left-sided whole-breast irradiation in DIBH using a hypofractionated protocol. While achieving excellent dose homogeneity and conformity in the target volume, OARs – especially cardiac and contralateral structures – received significantly less low-dose exposure compared to cVMAT. Compared with 3D-FiF, tVMAT achieved more homogeneous and conformal dose distributions and was less dependent on individual planner experience. Our findings encourage the implementation of tVMAT to achieve optimal target coverage with minimal organ-at-risk exposure. CLINICAL TRIAL REGISTRATION: Not applicable.