This study aimed to validate coronary artery calcium (CAC) scores as prognostic factors for acute coronary events (ACE) development in breast cancer patients with cardiac exposure to radiation. Researchers evaluated breast cancer patients who received (n = 511) or did not receive (n = 600) adjuvant radiotherapy (RT) between 2005 and 2013. CAC Agatston scores were analyzed using the deep-learning-based algorithm, AVIEW-CAC (Coreline Soft). The study found that CAC scores were a significant predictor of ACE in patients with breast cancer. Over a 9.3-year follow-up period, the 10-year ACE rate was 0.7%. The results suggest that CAC score screening on simulation CT in patients undergoing breast RT can help identify those with a high risk for ACE on a per-patient basis.