[en] Early breast cancer can be treated by conservative surgery followed by partial breast irradiation. This recent treatment replaces classical external beam whole breast radiotherapy. Several techniques are available but most experience does exist with interstitial catheter based brachytherapy. This well tolerated treatment shortens the treatment time and offers a good local control and cosmetic outcome, comparable to the best classical treatments, as confirmed by the first published results. These good results can only be obtained by rigorous patient selection and very precise 3D imaging and source implantation techniques.