Were We Able to Reduce Cardiac Doses in Breast Cancer Radiotherapy Over Time?

Objective: In this study, we aimed to review the heart and left coronary artery doses over the years in patients who received breast cancer radiotherapy (RT). Materials and Methods: A total of 436 breast cancer patients of 2 RT centers treated between the years 2010 and 2018 were included. The mean heart doses (HeartDmean-HDM) and left coronary artery mean doses (LDM) were analyzed using nonparametric tests. The conventional RT (CRT) was 50 Gy/2 Gy in 5 weeks, and the hypofractionated RT (HRT) was 40.05 Gy/2.67 Gy in 3 weeks. Boost was applied as 10-16 Gy/2 Gy for CRT and 10 Gy/2.5 Gy for HRT. An equivalent conventional total dose of 2 Gy/fraction (EQD2) was taken into account for HRT. Results: HDM was 107 +/- 104 cGy, and LDM was 288 +/- 209 cGy for the entire group. HDM was significantly lower in patients with breast-conserving surgery (99 +/- 94 cGy) than that in those with mastectomy (128 +/- 124 cGy) (p<0.001). Field-in-field intensity-modulated RT technique significantly reduced the doses compared to volumetric applications (104 +/- 95 cGy vs 141 +/- 38 cGy; p = 0.002). HDM was significantly increased with lymphatic RT (132 +/- 58 cGy vs 112 +/- 115 cGy; p<0.001). The addition of internal mammary volumes significantly increased HDM (p<0.001). No significant effect of boost was observed (p = 0.96). For both CRT and HRT regimens, HDM values were significantly lower after the year 2014 (right side p<0.001, left side p = 0.01). In the left side CRT, HDM was 1.74 Gy before 2014 and 1.3 Gy after 2014 and 1.0 and 1.19 Gy, respectively, for the right side. Conclusion: All efforts to reduce the cardiac doses will likely reduce long-term side effects.