Treatment Planning Comparison of Volumetric Modulated Arc Therapy With Trilogy and Halcyon for Bilateral Breast Cancer 

Abstract

Background: To evaluate the dosimetry of Halcyon in treatment of bilateral breast cancer with volumetric modulated arc therapy. Methods: On CT images of 10 patients with bilateral breast cancer, four Halcyon plans with different setup fields were generated and dosimetric comparisons were conducted among the four plans to select an optimal setup field mode. The four setup-field plans were referred to as CBCT-H, CBCT-L, MV-H, MV-L. Whole and partial arc plans on Trilogy and Halcyon referred to as T-4arc, T-8arc, H-4arc and H-8arc were designed. The dosimetric differences between whole and partial arc plans in the same accelerator were compared to understand the most suitable field setting mode. The better Halcyon plan was selected to the further dosimetric comparison of the plan quality and delivery efficiency between Trilogy and Halcyon. Results: CBCT-H plans increased Dmean, D2 and V107 of planning target volume (PTV) and V5 and Dmean of the heart, left ventricle (LV) and lungs compared to other plans. No significantly dosimetric differences were observed in PTV and organs at risk (OARs) among CBCT-L, MV-H and MV-L. The mean dose and low dose volume of heart, lungs and liver were significantly decreased in T-8arc plans. In terms of V5, V20, V30, V40 and Dmean of the heart, V20, V30, V40 and Dmean of the LV, V30, V40, Dmax and Dmean of the left anterior descending artery (LAD), V5 and V40 of lungs, H-8arc was significantly higher than H-4arc (p<0.05). Compared to Trilogy’s plans, Halcyon’s plans reduced the high-dose volume of the heart and LV, but increased the mean dose of the heart. For the dose of the LAD and the V20, V30 of lungs, there was no statistical difference between the two accelerators. Compared with Trilogy, plans on Halcyon significantly increased the skin dose, but also significantly reduced the delivery time. Conclusion: For Halcyon, the whole-arc plans has more dosimetric advantages in bilateral breast cancer radiotherapy. Although the mean dose of the heart and the skin dose are increased, the dose of the cardiac substructure and other OARs are comparable to the Trilogy, and the delivery time is significantly reduced.