Radiation-induced coronary artery disease (RI-CAD) is a significant cardiovascular complication for cancer survivors treated with thoracic radiation therapy (RT). Despite advances in RT techniques, exposure to the heart during treatment remains a critical factor influencing long-term cardiac outcomes, particularly in patients with breast and lung cancer. RI-CAD develops due to radiation-induced endothelial injury, inflammation, and accelerated atherosclerosis, presenting a unique and aggressive disease profile. This review explores the pathophysiology, risk factors, and diagnostic advancements for RI-CAD, emphasizing the role of PET in improving patient outcomes.