Study to See Whether Breath-Hold Techniques During RT Are Effective in Helping to Improve Sparing of the Heart

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