[Accelerated partial breast irradiation: bifractionated 40Gy in one week. A French pilot phase II study]

Abstract

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 (6MV) and an "en face" electron beam (6-22 MeV).

Results: The mean clinical target volume and planning target volume were respectively 15.1cm(3) (range: 5.2-28.7 cm(3)) and 117 cm(3) (range: 52-185 cm(3)). The planning target volume coverage was adequate with at least a mean of 99% of the volume encompassed by the isodose 40 Gy. The mean dose to the planning target volume was 41.8 Gy (range: 41-42.4 Gy). Dose inhomogeneity did not exceed 5%. Mean doses to the ipsilateral lung and heart were 1.6 Gy (range: 1.0-2.3 Gy) and 1.2 Gy (range: 1.0-1.6 Gy), 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.