Coronary Artery Dose-Volume Parameters Predict Risk of Calcification After Radiation Therapy

BACKGROUND: Radiation exposure increases the risk of coronary artery disease (CAD). We explored the association of CAD with coronary artery dose-volume parameters in patients treated with 3D-planned radiation therapy (RT). METHODS: Patients who received thoracic RT and were evaluated by cardiac computed tomography ≥ 1 year later were included. Demographic data and cardiac risk factors were retrospectively collected. Dosimetric data (mean heart dose, d(max), d(mean), V(50) - V(5)) were collected for the whole heart and for each coronary artery. A coronary artery calcium (CAC) Agatston score was calculated on a per-coronary basis and as a total score. Multivariable generalized linear mixed models were generated. The predicted probabilities were used for receiver operating characteristic analyses. RESULTS: Twenty patients with a median age of 53 years at the time of RT were included. Nine patients (45%) had ≥ 3/6 conventional cardiac risk factors. Patients received RT for breast cancer (10, 50%), lung cancer (6, 30%), or lymphoma/myeloma (4, 20%) with a median dose of 60 Gy. CAC scans were performed a median of 32 months after RT. CAC score was significantly associated with radiation dose and presence of diabetes. In a multivariable model adjusted for diabetes, segmental coronary artery dosimetric parameters (d(max), d(mean), V(50), V(40) V(30), V(20), V(10), and V(5)) were significantly associated with CAC score > 0. V(50) had the highest area under the ROC curve (0.89, 95% confidence interval, 0.80-0.97). CONCLUSIONS: Coronary artery radiation exposure is strongly correlated with subsequent segmental CAC score. Coronary calcification may occur soon after RT and in individuals with conventional cardiac risk factors.