Clinical Research Directory

Inclusion Criteria: * Aged greater than or equal to 50 years old * Histologically confirmed Infiltrating ductal carcinoma (IDC) or pure DCIS, less than or equal to 20mm maximum size. * Lobular carcinoma in situ (LCIS) is permitted. * Histologic grade I or II * Estrogen receptor (ER) +/- progesterone receptor (PR) positive in greater than or equal to 10% of cells and HER2 receptor-negative. * Tumour bed identifiable on imaging via surgical clips * Clear surgical margins * Sentinel nodes negative (at least one node taken if invasive and no isolated tumour cells) * No evidence of distant metastasis Exclusion Criteria: * Ink on surgical margins or positive histological margins * Lymphatic vessel invasion (LVI) * Bilateral breast cancer * Invasive lobular carcinoma * Pleomorphic LCIS * Multifocal or multicentric invasive cancer * Invasive carcinoma with associated DCIS greater than or equal to 30mm. * Patients receiving neoadjuvant chemotherapy, anti-HER2 agents or endocrine therapy * Patients receiving adjuvant chemotherapy or anti-HER2 agents. * Previous Hodgkin's lymphoma requiring mantle radiation * Prior radiation therapy to the ipsilateral breast * Triple-negative breast cancer * Documented mutation of BRCA1, BRCA2 or TP53, or at high genetic risk of breast cancer * Known inflammatory conditions associated with higher complications after RT, such as active scleroderma, systemic lupus erythematosus (requiring steroids or immune suppressive therapy) * Oncoplastic surgery where the primary tumour site is difficult to delineate * No previous cancer (except BCC or SCC of the skin) unless in remission beyond five years of diagnosis * People who are pregnant or planning to become pregnant * People who are unable or unwilling to comply with protocol requirements.