Long-term results from the NRG Oncology clinical trial NSABP B-39/RTOG 0413 comparing whole-breast irradiation (WBI) to accelerated partial-breast irradiation (APBI) indicated that, although the absolute difference between treatment was less than 1%, APBI did not meet the criteria for equivalence to WBI in controlling ipsilateral breast tumor recurrence (IBTR) after breast-conserving therapy. The trial provided the longest follow-up reported to date in the largest and most diverse group of patients treated with APBI; it is also the first study to include all forms of APBI. These results were published in The Lancet.
Trial participants on NSABP B-39/RTOG 0413 were randomly assigned to receive either WBI in 25 daily fractions of 2 Gy (50 Gy over five weeks) +/- a tumor bed boost (to 60 Gy) or APBI in 34 Gy of brachytherapy or 38.5 Gy of external-beam radiotherapy delivered in 10 fractions over 5 treatment days. The goal of the trial was to determine if treatment with APBI could shorten the treatment duration for patients while being equally as effective as WBI treatment.
Between March 2005 and April 2013, the trial enrolled 4,216 women and, of that group, 2,036 patients in the WBI group and 2,089 in the APBI group were available for survival analysis. At the 10-year follow-up, the cumulative incidence of IBTR was 4.6% (95% CI 3.7-5.7) in the APBI treatment group versus 3.9% (3.1-5.0) in the WBI treatment group. Treatment related toxicities and second cancers were similar between treatment groups.
"The value of our trial is that it has a large, diverse population of patients and sufficient power to demonstrate that APBI should not replace WBI in all types of patients who undergo lumpectomy. However, with an absolute difference of less than 1% in the 10-year cumulative incidence of IBTR, APBI might be chosen as an acceptable alternative for some women." said Frank Vicini, MD, principal investigator at the MHP Radiation Oncology Institute/21st Century Oncology in Pontiac, Michigan and Julia White MD, co-principal investigator at The Ohio State University. Dr. White added, "Differences in outcomes among the various forms of APBI, as well as quality of life (including patient-reported outcomes and cosmetic results), and quality assurance analyses will be reported separately"