The study hopes to determine whether patients with left-sided breast cancer are at an increased risk of cardiac changes due to radiation to the breast +/- Anthracycline-based chemotherapy +/- Herceptin and whether a deep inspiration breath hold (DIBH) technique during radiotherapy treatments would further reduce dosimetric dose to the heart as compared to the conventional free breathing (FB) technique thus reducing cardiac toxicity as measured by cardiac MRI using left ventricular end-diastolic volume (LVEDV) as a metric. Bio fluid samples will also be collected to investigate specific biomarkers of breast cancer: BNP, PIIINP and CITP

Patients with left-sided breast cancer who receive adjuvant breast or chest wall radiation have increased risk of treatment related cardiovascular morbidity. The risk of cardiac morbidity and mortality is increased when a patient receives radiation following adjuvant chemotherapy and Herceptin. The dose-volume histogram (DVH) parameters associated with increased cardiac toxicity include volume of heart irradiated, total radiation dose received by the left ventricle (LV), V25 and mean cardiac dose. Even though modern RT treatments like 3DCRT and IMRT can reduce the mean dose to the heart, the maximum dose to the left side of the heart/LV may not be reduced if the target is close to the heart. The hypothesis is that DIBH RT can safely and effectively reduce the heart dose, especially the dose to the LV, that could lead to reduction in the incidence of radiation induced cardiovascular morbidity and mortality.

Radiotherapy has detrimental effects on cardiac function due to remodeling of the cardiac tissue that receive radiation. We believe that the radiation related acute effects on heart tissue can be detected with cardiac functional MRI. The study will quantify the acute RT related effects. To our knowledge, cardiac MRI has not been explored as a non invasive technique to quantify RT +/- chemotherapy related effects.

Inclusion Criteria:

• Female patients with pathologically confirmed left sided breast cancer eligible for adjuvant breast/chest wall plus or minus regional nodal radiotherapy
• Women patients with age group between 18 and 70 years old
• Karnofsky performance score ≥ 70
• Ability to hold breath for at least 20 sec (for DIBH cohorts only)
• Life expectancy >10 years

Exclusion Criteria:

• For patients with prior Anthracycline based chemotherapy or Herceptin, if there is < 1.0 cm of heart on at least 3 slices ( 3 mm slices) on the FB scan, the patient will be considered a screen failure.
• Previously irradiated or recurrent breast/chest wall tumours or previous malignancy other than non-melanoma skin cancer unless disease free for a minimum of 5 years prior to study entry
• Patients that require a shell for breast immobilization
• Patients requiring a boost
• Stage IV disease