By Teh Lin, PhD, Associate Professor, Fox Chase Cancer Center
Accelerated partial breast irradiation (APBI) is an attractive treatment modality due to the shorter treatment time, similar local control and improved cosmetic outcomes compared with whole breast radiation therapy. Several clinical trials are also investigating APBI outcome with different dose fractionation schemes and compared them to whole breast irradiation or brachytherapy. The abstract authored by Naamit Kurshan Gerber, MD, from New York University Grossman School of Medicine “Five vs. Three Fractions of Prone Accelerated Partial Breast Irradiation: Results of a Randomized Controlled Phase 3 Non-Inferiority Trial” reports the update of clinical trial NCT 02276885 on 320 patients accrued between 2014 to 2021.
Dr. Gerber compared 30Gy in 5 fractions (5F) daily (control) to 24Gy in 3 fractions (3F) every other day dose scheme on post-menopausal women who had undergone breast-conserving surgery for invasive disease ≤ 2 cm (any grade) or for screen-detected ductal carcinoma in-situ ≤ 2.5 cm (grade 1-2), negative margins, and clinically or pathologically node negative as eligible patients. And she reported two endpoints on radiation fibrosis (grades 2+) and local recurrence (LR), regional recurrence (RR) distant metastasis (DM), contralateral breast cancer, and physician and patient rated cosmesis. Within two years, grade 2+ fibrosis occurred in 18.3% (25/137) of patients in the 5F arm and 12.3% (17/138) in the 3F arm meeting criteria for non-inferiority (lower edge of 95% CI -2.5%) but the rate of RFS including LR, RR or DM was 95% (3 deaths, 1 LR and 2 DM) (95% CI 88%-98%) in the 5F arm and 93% (5 LR, 1 RR, 4DM, and 5 deaths including 2 of the DM) (95% CI: 86%-96%) in the 3F arm with a median follow up of 54 months.
Dr. Gerber drew the conclusion, “APBI delivered prone with 24Gy in 3 fractions is non-inferior to 30Gy in 5 fractions with respect to fibrosis. This trial supports the use of APBI in this low-risk patient population and provides novelty with regard to an alternative fractionation scheme and the use of mini-tangents in the prone position.”
When APBI is safe for 3 fractions to further shorten the treatment duration for the patients, I would think the patient interactional setup will play a more important role with a lower fractioned treatment. More recent publications also investigate online adaptive radiation therapy with CBCT, surface guided tracking or even Cherenkov light tracking. They could be a perfect addition to the APBI lower fractionated radiation treatment as Dr. Gerber and her team proposed.
Abstract 237, Five vs. Three Fractions of Prone Accelerated Partial Breast Irradiation: Results of a Randomized Controlled Phase 3 Non-Inferiority Trial, was presented during the SS 24 - Breast 2: Partial Breast Irradiation session of ASTRO’s 66th Annual Meeting.
