Early side effects of three-dimensional conformal external beam accelerated partial breast irradiation to a total dose of 40 Gy in one week (A phase II trial)

Purpose: Several accelerated partial breast irradiation (APBI) techniques are described in the literature, and apparently, the three-dimensional (3D)-conformal technique is being used increasingly. Nonetheless, the optimal radiation dose is not yet known. Here, we report feasibility and early toxicities of APBI delivering 40 Gy over 5 days, in a phase II trial. Methods and Materials: From October 2007 to September 2008, 25 patients with pT1N0 cancer received 3D-conformal APBI. The prescribed radiation dose was 40 Gy in 4-Gy fractions given twice daily. This technique used two minitangents and an "en face" electron field. Toxicities were systematically assessed at 1, 2, and 6 months and then once every 6 months. Results: The planning tumor volume for evaluation (PTV-EVAL) coverage was adequate: the mean dose to the PTV-EVAL was 41.8 Gy (range, 41-42.4 Gy). 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. One and two months after completion of APBI, most patients had no or mild erythema (n = 16 patients at 1 month; n = 25 patients at 2 months); none of these patients developed moist desquamation. After a median follow-up of 12 months, only 1 patient had a significant moderate field contracture (grade 2). Other reported late toxicities were grade 1. Conclusions: 3D-conformal APBI (with two minitangents and an "en face" electron field) using a total dose of 40 Gy in 10 fractions twice daily over 5 days achieved appropriate PTV-EVAL coverage and offered significant sparing of normal tissue. Early tolerance was excellent.