First report of a randomized trial demonstrating non-inferior cosmetic outcome and local cancer control with the use of WBI with SIB is encouraging

Presenting author:
Juliane Hörner-Rieber, MD

By: Julia White MD, FASTRO

Following whole breast irradiation (WBI), the addition of a boost dose to the highest risk region of the breast around the lumpectomy cavity where most recurrences happen can significantly reduce ipsilateral breast cancer recurrence. Through advancements in radiation treatment and planning and evolved radiobiological understandings, daily simultaneous delivery of the boost dose to the highest risk region in the breast during WBI instead of its subsequent sequential delivery has been proposed. This would reduce the overall treatment course by a week on average, which is of particular interest to patients and providers during the COVID-19 pandemic. Dr. Hörner-Rieber et al. presents the outcome of the Phase III randomized MINT trial comparing one arm that delivers WBI with IMRT using Simultaneous Integrated Boost (SIB) versus 3-D CRT with sequential boost for breast cancer patients.

From 2011 to 2015, 502 women with indications for receiving a boost were randomly assigned post lumpectomy to receive breast irradiation with IMRT and SIB (50.4 Gy WBI and SIB 64.4 Gy in 28 fractions) versus with 3-D CRT and sequential boost (50.4 Gy WBI  plus 16 Gy  boost in 36 fractions). The primary endpoints were the local control rate measured at two and five years as well as the cosmetic results six weeks and two years post radiotherapy. The cosmetic results were evaluated via photo documentation calculating the relative breast retraction assessment (pBRA) score with the BCCT.core software and use of the four point (excellent, good, fair or poor) global cosmetic “Harvard” score as rated by patients and their physicians. 

With a median follow-up time of 5.1 years, the two-year cosmetic outcome in the SIB arm was non-inferior to that in the sequential boost arm as measured by the pBRA score as well as patient and physician rated global cosmetic scores. Similarly, the rates of local control for the SIB arm was 99.6% and was non-inferior to sequential boost, which had a local control rate of 99.6% (HR 0.602, 95%-CI: [0.123-2.452], p=0.487).

This first report of a randomized trial demonstrating non-inferior cosmetic outcome and local cancer control with the use of SIB is encouraging for this approach which reduces burden of care for patients undergoing breast conserving therapy. Confirmation of these findings from larger randomized trials using hypofractionated WBI (e.g. NRG RTOG 1005 and UK IMPORT HIGH) is awaited.

First 2-Year Results of the Multicenter, Randomized IMRT-MC2 Trial (MINT): Intensity-modulated Radiotherapy with Simultaneous Integrated Boost Versus 3-D Conformal Radiotherapy with Consecutive Boost for Breast Cancer Patients was presented on Saturday, October 24, in Scientific Session – SS 03 – Breast 01 – Techniques and Toxicities.

Published on: October 27, 2020