 Single dose intraoperative issued by electrontherapy or low energy photons 50 Kv is 21 Gy 5.11. However, these doses reported in the irradiated volume are not equivalent. Indeed, with electrontherapy, it is a complete volume of mammary parenchyma that is irradiated, whereas with low energy photon therapy X 50 KV is a shell of 5 mm thick which is treated knowing that to 10 mm from the surface of the sphere of treatment, the gland received only 50 of the dose initially prescribed. On interstitial brachytherapy with high dose rate, it has a dose escalation due to intrinsic volumes located within the irradiated area that will receive a higher dose than prescribed 12. It is this variation in dose within the target volume which can be efficiency, but also which can induce the toxicity of interstitial brachytherapy. The linear quadratic model to calculate the biological equivalence of 2 Gy irradiation scheme most often hypofractionned, is theoretically applicable for doses per fraction less than 8 Gy. Nevertheless, the authors using the IPAS intra-operative electrons, photons apply this method of calculation for doses of 21 Gy in one fraction. 