Purpose: The internal mammary arteries (IMA’s) are historically recognized to be protected against atherosclerosis. Whether chest wall-irradiation for breast cancer leads to significant IMA damage remains unclear. The utility of computed tomography (CT) and mammography to detect radiation-induced damage to the IMA’s and its branches is not known. The objective of this study is to assess the susceptibility of IMA’s to radiation-induced atherosclerosis, and the utility of CT scan and mammography in the assessment of IMA and its branches. Methods: A retrospective analysis of breast cancer patients who received chest wall-radiotherapy was performed. Patients with CT scans and/or mammograms \ge5 years post-radiotherapy were included. Baseline characteristics, coronary artery calcification (CAC), the presence of IMA damage assessed by CT scan, and IMA branch calcifications by mammography were recorded. Results: None of the 66 patients with CT scans post-radiotherapy revealed IMA atherosclerosis. There were 28 (42.4%) patients with CAC, of which four (14.3% of CAC subgroup or 6.1% of the total cohort) had calcifications on either side on mammogram (Chi-square test, p = 0.74). Out of the 222 patients with mammograms, 36 (16.2%) had IMA branch calcifications. Two hundred and ten patients received unilateral radiotherapy, and 27 (12.9%) of these patients had calcifications on the irradiated side, and 26 patients (12.4%) had calcifications on the contralateral side (OR = 1.0). Conclusion: IMA’s do not exhibit signs of radiation-induced atherosclerosis when evaluated by CT scan. In addition, there is no association between radiotherapy for breast cancer and the presence of IMA branch calcification on mammograms.