Partial Breast Re-irradiation Using Ultra Hypofractionation (PRESERVE)

Inclusion Criteria: * Age \> 18 years * In-breast recurrence or new primary (ductal carcinoma in situ (DCIS) or invasive carcinoma) * Tumour \<3.0 cm in greatest diameter on pathologic examination, including both invasive and non-invasive components * \>5 years after completion of prior adjuvant whole or partial breast radiotherapy (prior nodal radiotherapy permitted) * Clinically node negative * Negative margins (no tumour on ink) * Recovered from surgery with the incision completely healed and no signs of infection Exclusion Criteria: * Multicentric disease (patients with multifocal breast cancer in the same quadrant are eligible) * Tumour histology limited to lobular carcinoma only * T4 disease * Node positive or distant metastatic disease * Serious non-malignant disease (cardiovascular, pulmonary, systemic lupus erythematosus, scleroderma), which would preclude radiation treatment * Currently pregnant or lactating * Presence of an ipsilateral breast implant or pacemaker * Unable to commence radiation within 16 weeks of breast-conserving surgery (or last surgical procedure on the breast) or within 12 weeks from last cycle of adjuvant chemotherapy * Unable to clearly define the surgical cavity (oncoplastic procedures are permitted provided the tumor bed is well delineated with surgical clips). * Psychiatric disorders which would preclude obtaining informed consent or adherence to protocol * Grade II or more late skin toxicity from prior radiation evaluated and graded using CTCAE v5.0 * Current or prior diagnosis of bilateral breast cancer