Radiation dose to heart and cardiac substructures and risk of coronary artery disease in early breast cancer patients: A DBCG study based on modern radiation therapy techniques.

BACKGROUND: Coronary artery disease (CAD) has been reported as a late effect following radiation therapy (RT) of early breast cancer (BC). This study aims to report individual RT doses to the heart and cardiac substructures in patients treated with CT-based RT and to investigate if a dose-response relationship between RT dose and CAD exists using modern radiation therapy techniques. METHODS: Patients registered in the Danish Breast Cancer Group database from 2005 to 2016 with CT-based RT were eligible. Among 15,765 patients, the study included 204 with CAD after irradiation (cases) and 408 matched controls. Individual planning CTs were retrieved, the heart and cardiac substructures were delineated and dose-volume parameters were extracted. RESULTS: The median follow-up time was 7.3 years (IQR: 4.6-10.0). Among cases, the median mean heart dose was 1.6 Gy (IQR 0.2-6.1) and 0.8 Gy (0.1-2.9) for left-sided and right-sided patients, respectively (p < 0.001). The highest RT doses were observed in the left ventricle and left anterior descending coronary artery for left-sided RT and in the right atrium and the right coronary artery after right-sided RT. The highest left-minus-right dose-difference was located in the distal part of the left anterior descending coronary artery where also the highest left-versus-right ratio of events was observed. However, no significant difference in the distribution of CAD was observed by laterality. Furthermore, no significant differences in the dose-volume parameters were observed for cases versus controls. CONCLUSIONS: CAD tended to occur in the part of the heart with the highest left-minus- right dose difference, however, no significant risk of CAD was observed at 7 years' median follow-up.

Validation of a new open-source method for automatic delineation and dose assessment of the heart and LADCA in breast radiotherapy with simultaneous uncertainty estimation.

Radiotherapy has been shown to increase risks of cardiotoxicities for breast cancer patients. Automated delineation approaches are necessary for consistent and efficient assessment of cardiac doses in large, retrospective datasets, while patient-specific estimation of the uncertainty in these doses provides valuable additional data for modelling and understanding risks. In this work, we aim to validate the consistency of our previously described open-source software model for automatic cardiac delineation in the context of dose assessment, relative to manual contouring. We also extend our software to introduce a novel method to automatically quantify the uncertainty in cardiac doses based on expected inter-observer variability (IOV) in contouring. This method was applied to a cohort of 15 left-sided breast cancer patients treated in Denmark using modern tangential radiotherapy techniques. On each image set, the whole heart and left anterior descending coronary artery (LADCA) were contoured by nine independent experts; the range of doses to these nine volumes provided a reference for the dose uncertainties generated from the automatic method. Local and external atlas sets were used to test the method. Results give confidence in the consistency of automatic segmentations, with mean whole heart dose differences for local and external atlas sets of -0.20 ± 0.17 and -0.10 ± 0.14 Gy, respectively. Automatic estimates of uncertainties in doses are similar to those from IOV for both the whole heart and LADCA. Overall, this study confirms that our automated approach can be used to accurately assess cardiac doses, and the proposed method can provide a useful tool in estimating dose uncertainties.

Radiation-induced risk of ischemic heart disease following breast cancer radiotherapy in Denmark, 1977-2005.

BACKGROUND AND PURPOSE: The increase in the risk of heart disease from incidental exposure of the heart during radiotherapy for breast cancer has been estimated previously from retrospective data in Danish and Swedish women. Here we present an analysis of the Danish material updated with new cases and controls, extended follow-up period, and with refined dose estimates using simulator films or CT data. MATERIAL AND METHODS: From the database of the Danish Breast Cancer Cooperative Group, we identified 531 women diagnosed with early-stage breast cancer from 1977 to 2005, who developed subsequent ischemic heart disease (cases) and matched them to 1069 controls without heart disease after radiotherapy. Data were available for precise dose estimation for 196 cases and 413 controls receiving tangential photon techniques. RESULTS: The median of the mean heart doses for the women receiving tangential radiotherapy was 2.41 Gy for left- and 0.68 Gy for right-sided radiotherapy. The mean heart dose was higher for cases than controls (0.84 Gy and 0.71 Gy, respectively; p < 0.001). In this group, the linear increase in the excess odds ratio of major coronary events per gray of mean heart dose (K) was 19 percent (95% Confidence Interval(CI) 1% to 63%, p = 0.02). For patients treated with electron techniques, there was no significant association between mean heart dose and the risk of major coronary events (K = -0.05, 95% CI -12% to 9%, p = 1.00). CONCLUSION: The increase in the excess odds of major coronary events per gray mean heart dose using individual dose estimates is higher than previously reported.