Impact of patient and treatment characteristics on heart and lung dose in adjuvant radiotherapy for left-sided breast cancer

Purpose The heart and lungs are routinely exposed to incidental irradiation during adjuvant radiotherapy (RT) of breast cancer. We analyzed the impact of patient and treatment characteristics on heart and lung dose in left-sided breast RT. Methods We analyzed 332 female patients treated with left-sided breast RT between 2013 and 2018. Mean heart dose (MHD), left mean lung dose (MLD) and heart / lung V-20Gy were collected from treatment plans. Patients were stratified by RT technique (3D-conformal RT, 3DCRT; intensity-modulated RT, IMRT; volumetric modulated arc therapy, VMAT) and target volumes, including lymph node RT (LN-RT). Patient characteristics (body mass index (BMI), heart and lung volume) were assessed using correlation analyses. Results LN-RT was performed in 111 patients with increased MHD (median 4.6 vs. 3.3 Gy; p < .01), left MLD (14.8 vs. 7.7 Gy; p < .01) and left lung V-20Gy (30.0% vs. 14.4%; p < .01) compared to treatment without LN-RT. Internal mammary LN-RT further increased organ doses compared to RT involving only supraclavicular +/- axillary LN (p < .01 for all values; MHD 6.9 vs. 4.2 Gy). In 221 patients treated without LN-RT, IMRT/VMAT was associated with higher left lung doses (MLD 9.1 vs. 7.4 Gy, p < .01; V-20Gy 18.8% vs. 14.0%, p < .01) compared to 3DCRT. A negative correlation between total lung volume and both MHD (r = - 0.38; p < .01) and heart V-20Gy (r = - 0.37; p < .01), as well as a weak positive correlation of BMI and MHD (r = 0.27; p < .01) were observed. Conclusions In adjuvant RT for left-sided breast cancer, LN-RT is associated with a marked increase in heart and lung doses, particularly with internal mammary LN-RT. Potential advantages of IMRT/VMAT for breast or chest wall RT need to be weighed against a moderately increased lung dose.