Evaluating improvements in cardiac dosimetry in breast radiotherapy and comparison of cardiac sparing techniques

Purpose/objective(s) Data from Darby et al. demonstrated that cardiac dose in patients undergoing breast radiation therapy is associated with cardiac events. Cardiac dose is primarily dependent on treatment laterality and treatment fields. More recently, techniques such deep inspiratory breath hold (DIBH) and prone positioning have been used as cardiac sparing techniques. The purpose of this study is to assess changes in cardiac dosimetry with cardiac sparing techniques. Materials/methods This retrospective study included breast cancer patients treated from 2010 to 2018 at a single institution. Mean heart dose (MHD) was analyzed with respect to treatment era, laterality, cardiac sparing technique, and treatment fields, including regional nodal irradiation (RNI) and internal mammary nodal irradiation (IMNI). Results Seven hundred sixty-five patients were included in this study. Average MHD was 1.87 Gy for left-sided cases and 0.71 Gy for right-sided cases (p < 0.0001). For left-sided cases, the average MHD without RNI, RNI without IMNI, and RNI with IMNI was 1.40 Gy, 2.01 Gy, and 3.48 Gy respectively. For left-sided cases without RNI, the average MHD decreased from 1.61 to 1.22 Gy using DIBH (p < 0.0001), and to 1.02 Gy with prone positioning (p < 0.0001). There was no difference in MHD between DIBH and prone techniques (p = 0.44). For left-sided cases with RNI, DIBH reduced the average MHD from 2.4 to 2.1 Gy (p = 0.04). Following the 2013 publication of Darby et al., the average MHD significantly decreased for left-sided RT cases (2.02 vs. 1.83 Gy, p = 0.03) due to increased institutional adoption of cardiac-sparing techniques. Conclusion Cardiac doses were lower following the 2013 publication of Darby et al. due to greater use of cardiac sparing techniques. Overall, the average MHD was < 1 Gy and < 2 Gy for right and left breast cancers, respectively, with lower doses achieved using DIBH and prone positioning as cardiac sparing techniques.