tude pilote française de phase II d»irradiation partielle acclre du sein conformationnelle tridimensionnelle bi-fractionne hebdomadaire de 40

Purpose: Since 2009, accelerated partial breast irradiation (APBI) in North America has been allowed to be used for selected group of patients outside a clinical trial according to the ASTRO consensus statement. In France, accelerated partial breast irradiation is still considered investigational, several clinical trials have been conducted using either intraoperative (Montpellier) or Mammosite^® (Lille) or brachytherapy modality (PAC GERICO/FNCLCC). Here, we report the original dosimetric results of this technique. Patients and methods: Since October 2007, Institut Gustave-Roussy has initiated a phase II trial using 3D-conformal accelerated partial breast irradiation (40. Gy in 10 fractions BID in 1. week). Twenty-five patients with pT1N0 breast cancer were enrolled and were treated by two minitangent photons beams (6. MV) and an "en face" electron beam (6-22. MeV). Results: The mean clinical target volume and planning target volume were respectively 15.1cm³ (range: 5.2-28.7cm³) and 117cm³ (range: 52-185cm³). The planning target volume coverage was adequate with at least a mean of 99% of the volume encompassed by the isodose 40Gy. The mean dose to the planning target volume was 41.8Gy (range: 41-42.4Gy). Dose inhomogeneity did not exceed 5%. Mean doses to the ipsilateral lung and heart were 1.6Gy (range: 1.0-2.3Gy) and 1.2Gy (range: 1.0-1.6Gy), respectively. Conclusion: The 3D conformal accelerated partial breast irradiation using two minitangent and "en face" electron beams using a total dose of 40. Gy in 10 fractions BID over 5. days achieves appropriate planning target volume coverage and offers significant normal-tissue sparing (heart, lung). Longer follow-up is needed to evaluate the tissue tolerance to this radiation dose.