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In women amenable to breast conserving surgery, lumpectomy (L) followed by adjuvant whole breast irradiation (WBI) is the standard of care. Randomized trials have demonstrated that a lumpectomy cavity (LC) boost reduces recurrence but increases breast fibrosis (BF).  Oncoplastic reconstruction (OPR) techniques are increasingly being used  to help improve or preserve cosmetic outcomes. Women that undergo OPR represent especially difficult cases for LC delineation on CT scans used for adjuvant WBI planning.  We designed a multi-center prospective protocol incorporating an intraoperative electron radiation therapy (IOERT) LC boost in women undergoing L+OPR with a hypothesis that IOERT boost followed by WBI will result in acceptably low rates of grade 3 BF.  Here, we present the results of our protocol specified interim safety analysis.

This is a single arm phase II study (NCT0297912) of IOERT boost (8 Gy x 1 to the 90% isodose line) followed by adjuvant WBI (40 Gy/15 fractions or 50 Gy/25 fractions) or adjuvant WBI+regional nodal irradiation (RNI) [50 Gy/25 fractions].  Inclusion criteria include stage I-III breast cancer with intent to undergo L+OPR with LC boost. The primary endpoint is the 1-year rate of grade 3 BF. The first 30 patients will be used to determine the safety of the study (rate of complications involving the breast treated with IOERT resulting in readmission/return to surgery within 30 days of IOERT).  We deemed a >15% incidence rate of these complications unacceptable.  Based on the exact binomial distribution with a hypothesized probability of success of 0.15, the study would be halted if ≥9 of 30 patients experienced a complication.  

The first 30 patients were enrolled from 10/6/2017-8/22/2019.  The median age is 55 years (range, 40-74 years) with clinical stage distribution of I (N=19),II (N=10), or III (N=1).  Breast cancer subtype is (ER+ or PR+)/HER2- in 25, HER2+ in 4, and triple-negative in 1. OPR techniques included 25 reduction mammoplasties and 5 local tissue rearrangements, of which 6 were performed by the breast surgeons and the remainder by plastic surgeons. IOERT was delivered using 6 MeV electrons (N=3), 9 MeV electrons (N=8) or 12 MeV electrons (N=19) to a median depth of 3.1 cm (range, 1.8-3.6 cm) with a median applicator size of 5.5 cm (range, 4-7 cm).  The complication rate was 10%(N=3): 2 hematomas requiring evacuation and 1 breast cellulitis requiring IV antibiotics.  To date, 28 of the 30 patients have received adjuvant WBI (N=24 WBI to 40 Gy/15 and N=4 WBI+RNI to 50 Gy/25) at a median of 7.7 weeks (range, 5.3-12.3 weeks) after IOERT.  The remaining 2 patients are completing chemotherapy.

Given the low rate of postoperative complications, this study has been deemed  safe and will continue to the accrual goal of 176.  This is the first prospective evaluation of the use of an IOERT boost in patients undergoing L+OPR, and the final results may result in a new treatment paradigm for women undergoing OPR.