Non-coplanar Volumetric Modulated Arc Therapy for Locoregional Radiotherapy of Left-sided Breast Cancer Including Internal Mammary Nodes

BACKGROUND: Non-coplanar volumetric modulated arc therapy (ncVMAT) is proposed to reduce toxicity in heart and lungs for locoregional radiotherapy of left-sided breast cancer, including internal mammary nodes (IMN). PATIENTS AND METHODS: This retrospective study included 10 patients with left-sided breast cancer who underwent locoregional radiotherapy after breast-conserving surgery. For each patient, the ncVMAT plan was designed with four partial arcs comprising two coplanar arcs and two non-coplanar arcs, with a couch rotating to 90°. The prescribed dose was normalized to cover 95% of planning target volume (PTV), with 50 Gy delivered in 25 fractions. For each ncVMAT plan, dosimetric parameters were compared with the coplanar volumetric modulated arc therapy (coV-MAT) plan. RESULTS: T here were improvements in conformity index, homogeneity index and V(55) of total target volume (PTVall) comparing ncVMAT to coVMAT (p < 0.001). Among the organs at risk, the average V(30), V(20), V(10), V(5), and mean dose (D(mean)) of the heart decreased significantly (p < 0.001). Furthermore, ncVMAT significantly reduced the mean V(20), V(10), V(5), and D(mean) of left lung and the mean V(10) and V(5) and D(mean) of contralateral lung (p < 0.001). An improved sparing of the left anterior descending coronary artery and right breast were also observed with ncVMAT (p < 0.001). CONCLUSIONS: Compared to coVMAT, ncVMAT provides improved conformity and homogeneity of whole P TV, better dose sparing of the heart, bilateral lungs, left anterior descending coronary artery (LAD), and right breast for locoregional radiotherapy of left-sided breast cancer with IMN, potentially reducing the risk of normal tissue damage.