More APBI outcomes.

Top Line: Are local control outcomes with interstitial brachytherapy ABPI comparable to whole breast radiation?

The Study: There are multiple techniques for delivering accelerated partial breast irradiation. Randomized trials of various APBI techniques have had mixed results with respect to local control and cosmesis. Here we have 10-year outcomes from the GEC-ESTRO trial comparing exclusive interstitial brachytherapy APBI and whole breast radiation. 1184 patients eligible for analysis had ≤3 cm tumors with ≤pNmi disease, no LVI, and at least 2 mm margins (5mm for any DCIS). In the WBRT arm, everyone received 50-50.4 Gy in 25-28 fractions with a 10 Gy in 5 fractions boost. In the APBI arm, the CTV was defined on pre- and post-implant CT and consisted of the tumor bed with at least a 2 cm margin. Both HDR and pulsed-dose-rate brachytherapy were used. For HDR, the prescription was either 32 Gy in 8 BID fractions or 30.1 Gy in 7 BID fractions. For PDR, the prescription was 50 Gy given at 0.6-0.8Gy/h. Treatment planning goals were to have at least 90% of the target receive the prescribed dose and to keep the ratio of V100:V150 <0.35. The skin max was limited to 70% of the prescribed dose. At 10 years, the rate of local recurrence was 3.51% after APBI and 1.58% after WBRT. This difference was not statistically significant (p=0.074). The rate of regional recurrence was 1.19% v 0.39%. The rate of late grade 3 toxicity was lower in the APBI arm (1% v 3%). There was no difference in physician-rated cosmesis, but patients reported a higher rate of excellent cosmesis after APBI (45% v 34%).

TBL: At 10 years, the rate of local recurrence after APBI using interstitial brachytherapy (3.51%) was numerically but not significantly higher than whole breast RT with boost (1.58%) and the rate of late grade 3 toxicity was lower. | Strnad, Lancet Oncol 2023