Non-coplanar volumetric modulated arc therapy for locoregional radiotherapy of left-sided breast cancer including internal mammary nodes

Abstract 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.