Radiotherapy (RT) has a major curative role in women with early breast cancer, and is recommended routinely after lumpectomy and selectively after mastectomy. It has contributed to a halving of breast cancer mortality in the UK over the last 2 decades despite ever-rising cancer incidence. RT in women with left-sided tumours often exposes the underlying heart to a damaging dose. The heart is very sensitive to RT, and there were 1-2 deaths from heart disease for every 100 breast cancer patients treated during the 1960s-70s. The situation has improved in recent years, but standard RT techniques still deliver significant radiation doses to heart tissue.

Two potentially simple techniques reduce heart dose. In one, women are taught to breathe in deeply and to hold their breath for about 20 seconds while RT is given. The downward movement of the diaphragm pulls the heart away from the RT beam. In the other technique, women lie on their fronts, instead of on their backs as they normally do for breast RT. In this position, the breast falls away from the rib cage and reduces exposure of the heart. Neither technique is routinely available to women receiving breast RT in the UK for reasons that this research aims to address. The investigators need to: 1) confirm that patient position can be reproduced with millimetre precision every day using these techniques, 2) minimise costs of equipment, time and personnel required to support such techniques, 3) select the most appropriate technique for different patients and 4) train staff in centres across the UK to deliver techniques safely and effectively. By addressing all of these issues, the study aims ultimately to make heart-sparing RT available to all UK women that might benefit from treatment, thereby significantly reducing the burden of heart disease in breast cancer survivors.

Inclusion Criteria:

• Complete microscopic excision of early stage invasive ductal or lobular carcinoma (pT1-3b N0-1 M0) of the left breast following breast conservation surgery or mastectomy.
• Recommendation for whole breast (groups A and B) or chest wall (Group A only) radiotherapy (with or without tumour bed boost)
• Age ≥18
• Performance status ≤1
• Patients able to tolerate breath-hold

Exclusion Criteria:

• Requirement for nodal irradiation
• Patients with micro- or macro-scopic disease on sentinel node biopsy who have not undergone completion axillary node clearance
• Previous radiotherapy to any region above the diaphragm