Inclusion Criteria:

• * ≥18 years of age
• * Non-metastatic Breast Cancer patients who are scheduled to receive conventional left-sided or bilateral breast/chest wall RT inclusive of treatment to the internal mammary lymph nodes (IMNs)
• * Prior chemotherapy is permitted
• * Ability to understand and the willingness to sign a written informed consent document
• * No contraindication to MRI
• * Patients with right-sided breast cancer or patients with left-sided patients not requiring treatment to the IMNs, but where cardiac anatomy is determined to be unfavorable by the study PI, will be considered eligible.

Exclusion Criteria:

• * Person who is pregnant or breastfeeding.
• * Patients receiving any other investigational agent will not be excluded from study eligibility, unless the patient is already enrolled in an interventional study evaluating cardiac toxicity. No cytotoxic therapy or radiotherapy may be used during radiation therapy.
• * Contra-indication to gadolinium contrast (e.g., chronic kidney disease)
• * Contra-indication to radiotherapy (e.g., scleroderma, p53 mutation)