Doses to the right coronary artery and the left anterior descending coronary artery and death from ischemic heart disease after breast cancer radiotherapy: a case-control study in a population-based cohort

Background and purpose: Doses to the coronary arteries in breast cancer (BC) radiotherapy (RT) have been suggested to be a risk predictor of long-term cardiac toxicity after BC treatment. We investigated the dose-risk relationships between near maximum doses (D max ) to the right coronary artery (RCA) and left anterior descending coronary artery (LAD) and ischemic heart disease (IHD) mortality after BC RT. Patients and methods: In a cohort of 2,813 women diagnosed with BC between 1958 and 1992 with a follow-up of at least 10 years, we identified 134 cases of death due to IHD 10-19 years after BC diagnosis. For each case, one control was selected within the cohort matched for age at diagnosis. 3D -volume and 3D -dose reconstructions were obtained from individual RT charts. We estimated the D max the LAD and the mean heart dose (MHD). We performed conditional logistic regression analysis comparing piecewise spline transformation and simple linear modeling for best fit. Results: There was a linear dose-risk relationship for both the D max to the RCA (odds ratio [OR]/Gray [Gy] 1.03 [1.01-1.05]) and the LAD (OR/Gy 1.04 [1.02-1.06]) in a multivariable model. For MHD there was a linear dose-risk relationship (1,14 OR/Gy [1.08-1.19]. For all relationships, simple linear modelling was superior to spline transformations. Interpretation: Doses to both the RCA and LAD are independent risk predictors of long-term cardiotoxicity after RT for BC In addition to the LAD, the RCA should be regarded as an organ at risk in RT planning. to the RCA and