Stereotactic Body Radiation Therapy for Breast Cancer

Inclusion Criteria: Histologically confirmed diagnosis of invasive breast carcinoma of non-lobular histology. Unifocal tumour Previously assessed by a breast surgeon and medical oncologist, with no surgery being recommended at time of enrollment. Primary breast and axillary surgery not recommended/performed due to any of the following: * distant metastatic disease * unresectable T4 disease and/or * medically inoperable and/or * patient declined breast surgery Stages T1-T4, N1-N2, M0-M1 disease Ability to attend radiation planning and therapy, able to attend for follow-up care Able to provide written informed consent. Exclusion Criteria: Received chemotherapy within 3 weeks prior to breast SBRT. (Concurrent endocrine therapy is permitted) Multifocal or multicentric tumours. Ipsilateral supraclavicular or infraclavicular nodal disease \>= 1cm size that is at the level of or superior to the brachial plexus Unable to meet the brachial plexus dose constraints despite compromising coverage of target volumes - as per the discretion of the treating physician Treatment target volume estimated to occupy \> 50% of the ipsilateral whole breast volume. Locally recurrent breast cancer, with previous radiotherapy to the breast, or previous lumpectomy or mastectomy. Ipsilateral breast implant. Serious non-malignant disease that precludes definitive surgical or radiation treatment (e.g. scleroderma, systemic lupus erythematosus, cardiovascular/pulmonary/renal disease). Women who are pregnant or lactating. Psychiatric or addictive disorders that preclude obtaining informed consent or adherence to protocol