Breast cancer is a leading cancer among Bangladeshi female. For breast cancer, there are different available treatment options according to the stage of disease. One of the important ones is radiotherapy (RT). Various side effects can occur during and after RT. Among the late side effects, numerous cardiac and pulmonary problems are significant specially in case of left sided breast cancer. In such cases, patients are being cured from cancer but the treatment itself endangering patients' general health and wellbeing by increasing risk of future life threatening cardiac and pulmonary diseases. Studies from around the world have shown that, during RT of left sided breast cancer, holding the breath for certain time after deep inspiration can reduce the radiation doses to heart and left lung without compromising doses to the chest wall. As a result, they can avoid the extra risk of treatment related late toxicities. This study will look at the utility and efficacy of Deep Inspiration Breath Hold (DIBH) RT over free breathing (FB) RT in reducing the heart and left lung doses without compromising the dose to the target volumes in left sided post mastectomy breast cancer patient, which is the main objective of this study.

Inclusion Criteria:

1. Histopathologically proven left sided invasive breast cancer patients who underwent modified radical mastectomy.
2. Post mastectomy patients for whom radiotherapy including supraclavicular irradiation is indicated.
3. Patients having ECOG performance status up to 1.

Exclusion Criteria:

1. Left sided breast cancer patient underwent BCS.
2. Patient received any chemotherapy other than Doxorubicin, Cyclophosphamide and taxane (Paclitaxel/ Docetaxel) in any settings (neoadjuvant or adjuvant).
3. Patients who have comorbidities that would hinder DIBH (extreme obesity, mental disorder, hypoacusis etc.).
4. Known case of patients with respiratory diseases.
5. Known case of patients with ischemic heart diseases.
6. Patients with previous history of radiotherapy to chest.
7. Male breast cancer patients.
8. Bilateral breast cancer patients.
9. Pregnant or lactating women.
10. Age ˂ 18 years.