IRMA.

Top Line: Does accelerated partial breast irradiation (APBI) delivered in BID fractions with external beam radiation have cosmesis comparable to whole breast radiation?

The Study: In the RAPID trial, 38.5 Gy in 10 BID fractions resulted in a 36% rate of fair/poor cosmesis compared to 19% with whole breast radiation. IRMA is another large randomized trial comparing APBI and whole breast RT. A whopping 3309 patients with early stage breast cancer were randomized to whole breast radiation using either conventional or moderate hypofractionation +/- boost or APBI with no boost. APBI consisted of 38.5 Gy in 10 BID fractions delivered over 5 days. Here is a report of 5-year toxicity and cosmetic outcomes. At baseline, 12% of patients in both arms reported fair/poor cosmesis prior to treatment. At 1, 3, and 5 years the rates of fair/poor cosmesis for APBI v WBRT were 10.1% v 10.6%, 12.7% v 9.2%, and 14% v 9.8%. The differences at years 3 and 5 were significantly higher with APBI. As we can see, though, the difference arose because fair/poor cosmesis declined in the WBRT arm while it slightly rose in the APBI arm. The rate of acute grade 3+ skin toxicity was low, but significantly higher after WBRT (1.3% v 0.1%). In the APBI arm, there were more late soft tissue and bone toxicity events. One hypothesis that has emerged from the APBI trials is that delivering 38.5 Gy over 5 days results in a higher than anticipated biological dose and hence worse soft tissue toxicity. In fact, the single-arm OPAL trial delivered 35 Gy APBI in 10 daily fractions and found that cosmesis was similar to that of WBRT. 

TBL: IRMA confirms that fair/poor cosmesis is slightly higher when APBI is delivered using 38.5 Gy in 10 BID fractions. | Meduri, J Clin Oncol 2023