Population based audit of heart radiation doses in 6925 high-risk breast cancer patients from the Danish breast cancer group RT Nation study

Background and purpose: In this study, we conducted a population-based retrospective audit of heart doses for high-risk breast cancer (BC) over a nine-year period in patients treated with adjuvant CT-based radiotherapy in a comprehensive and homogenized national BC cohort. Additionally, this serves as a demonstration of performing large scale audits with consistent delineations created by an auto-segmentation tool. Materials and methods: High-risk BC patients treated with adjuvant radiotherapy in the period 2008–2016 from all seven radiotherapy centres in Denmark were included. A homogenized cohort was created using an inhouse developed auto-segmentation tool. The homogenized cohort volume and planned doses (mean heart dose (MHD), V20Gy and V40Gy) were evaluated. Volumes and dose metrics were compared for clinical and homogenized heart volumes. Results: Among 6925 patients, 5589(81 %) had a clinical heart delineation. The median delineated heart volume increased from 531.9 ml (2008) to 638.5 ml (2016) (p < 0.01). The median MHD for the homogenized cohort was 1.58 Gy (2008–2016) with an overall decreasing trend, 2.14 Gy in left- and 1.08 Gy in right-sided patients. The median MHD in the clinically delineated hearts was 0.01 Gy lower than the planned median MHD in the homogenized cohort. Conclusion: During 2008–2016 the planned heart dose has been low across the population. A volume increase was observed in the clinically delineated hearts, however the median MHD in the homogenized cohort was low, with 1.58 Gy. The study demonstrated the possibilities for full population-based and consistent dose audit by using auto-segmentation tools.