Breast cancer (BC) radiotherapy (RT) can induce coronary artery disease arising many years after exposure. Little is known on mid-term coronary artery calcium (CAC) progression and association with unavoidable cardiac radiation exposure, which might provide insight into ongoing current disease activity and eventually optimize primary and secondary prevention.

The BACCARAT prospective longitudinal study was to compare CACscores determined before the radiotherapy with those determined 2years afterwards and to evaluate whether cardiac exposure, determined by heart, left ventricle and coronary arteries dose, was associated with the occurrence of calcified progressors.

This study included BC patients treated with RT without chemotherapy. Based on CAC CT scans performed before RT and 2years after, calcified progressor was defined as an increase in CAC score based on two definitions: P1 for CACscoreV24-CACscoreV0>0; P2 for increase of CAC class (0 for class 0; 0.1–10; 10–100 for class III; 100–400 for class IV and>400 for class IV). Dosimetry data was collected for whole heart, left ventricle and each coronary artery. Logistic regression models were used to assess the association between doses and the risk of calcified progressor with odds ratios (OR) and their 95% confidence intervals (CI).

Changes in CAC scores were analysed in 101 BC patients (84 LBC and 17 RBC). Mean age was 58.4years. Mean doses to the heart and the left ventricle were 2.5Gy and 4.6Gy respectively (3.0Gy and 6. Gy respectively for left-sided BC; 0.5Gy and 0.1Gy respectively for right-sided BC). The LAD [AR1] was the most exposed coronary artery with 16.0Gy for left-sided BC. CAC score was 0 for 76 patients (75%), decreased to 71 patients (70%). We observed 29 P1 progressors and 13 P2 progressors. Mean dose to the left ventricle was the only cardiac structure dose significantly associated with the risk of P1 (OR=1.15; 95% CI: 1.02–1.30; P=0.023) and P2 (OR=1.19; 95% CI: 1.01–1.41; P=0.038). These results remained significant after adjustment for age but no longer after further adjustment for cardiac treatment and diabetes.

Left ventricle exposure may be a good predictor regarding the risk of mid-term calcified progressor for BC patients treated with RT. However, the sample size of this study is limited, and further investigations remain required.