Single Fraction Elderly Breast Irradiation (SiFEBI)

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. In our study, we propose to treat these patients with a total dose of 16 Gy in one fraction. This dose is calculated taking into account a report alpha/beta for the breast, on the order of 3.4 Gy for late toxicity and 4.6 Gy for local control (13). Applying the linear-quadratic model with alpha/beta for the breast of 4, 16 Gy in one fraction is calculated as radio-biologically equivalent to 53 Gy in conventional fractionation (14,15). Biological Equivalence of this dose is between the dose in the protocols IPAS intraoperative electron or X-ray photons of 50 kV (21 Gy in one fraction, 87 Gy EQD2 alpha/beta 4.6) (5.8) and the post-operative irradiation of 34-38 Gy in 10 fractions, 5 days (42 Gy EQD2 alpha/beta 4.6.