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. A retrospective analysis of breast cancer patients who received chest wall-radiotherapy was performed. Patients with CT scans and/or mammograms ≥5 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. 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). 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.