TARGIT is an international randomised clinical trial designed to test the hypothesis that the strategy of delivering a single dose of targeted intraoperative radiotherapy (IORT) in patients eligible for breast conserving therapy (with the addition of whole breast radiotherapy in those patients at high risk of recurrence elsewhere in the breast [e.g. lobular carcinomas and extensive intraductal component]) is non-inferior to a conventional course of post-operative external beam radiotherapy (EBRT) delivered over several weeks. The primary endpoints are local recurrence in the conserved breast. It is a pragmatic trial in which each participating centre has the option to define more restrictive entry criteria than in the core protocol. Only centres with access to the INTRABEAM may enter patients into the trial. Eligible patients are those 45 years or older and suitable for breast conserving surgery. After giving consent patients are randomised to either TARGIT group or to EBRT group. They may receive any other adjuvant treatments as deemed necessary. The protocol requires that patients be followed at six monthly intervals for five years and then annually.