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Hypofractionation radiation therapy in breast cancer are well- established treatment schedules. However, in left-sided breast cancer, the doses to heart and cardiac substructures are not well defined. In this study, we compare the radiation dose received by cardiac and the substructures in left-sided breast cancer.

Total 30 patients with histopathologically proven ductal carcinoma in left sided breast cancer, 15 each treated with 26Gy in 5 fractions (Group A) and 40Gy in 15 fractions (Group B) respectively. Planning Computerised Tomography (CT) was undertaken for each patient and organs at risk including the cardiac substructures, whole breast, heart, lungs, and contra lateral breast was contoured for each patient. Radiotherapy plans were made by standard tangent field. Mean and maximum heart dose, LAD, RCA, LCA and Left circumflex artery mean and V5 of right lung, and mean, V5, V10 and V20 of left lung, mean dose and V2 of contra lateral breast were calculated for each patient and compared using student’s T test.

Mean doses to the heart were 16.4Gy and 8.45Gy respectively and left lung mean dose, V5, V10 and V20 were 5.91Gy, 14%, 12.8%, 11.7%; and 7.83Gy, 20.4%, 18.6% and 14.7% in group A and B, respectively. The dose to the distal LAD was significantly higher than proximal LAD both in both plans (p<0.001) signifying the need for contouring the distal LAD. Similarly, the doses were reduced in left circumflex artery with group with trending towards significance. There was no statistically significant difference in the doses to the other cardiac substructures in both groups. Mean dose to the right lung was significantly less in group A as compared to BCS, 0.31Gy vs. 0.64Gy, respectively (p = 0.027). Mean dose to the opposite breast was 0.52Gy and 0.37Gy respectively. 

Our study emphasizes the need for contouring the cardiac substructures especially the distal LAD and Left circumflex artery. The hypofractionation schedule with 26Gy in 5 fractions has shown benefit in reducing doses to these cardiac substructures. There is a need for clinical studies to validate the results.