left-sided breast cancer stage i-iii.

indications for adjuvant regional nodal and breast or chest wall radiation therapy (rt).

women and men are allowed.

must be at least 18 years old at time of consent.

pregnant and/or breastfeeding women or patients of child-producing potential not willing to use contraception while on study.

prior history of cardiovascular disease per physician discretion.

stage 0 and iv breast cancer.

prior radiation therapy to chest.

concurrent trastuzumab per physician discretion.

contraindications to cardiac mri (e.g., contrast reaction, metal implants, etc.).