Acute Toxicity and Cosmesis Following a Tumor Bed Boost After Whole Breast Moderate Dose Hypofractionation

Randomized evidence suggests that tumor bed boost improves local control following whole breast radiation therapy (WBRT) but may lead to more acute and late toxicity. However, little data are available about toxicity in real world practice from a tumor bed boost delivered after WBRT, particularly following moderate dose hypofractionation (MH). We evaluated acute toxicity and cosmesis effects associated with use of a boost after MH-WBRT in a large prospective cohort.

This analysis includes women undergoing adjuvant MH-WBRT without regional nodal irradiation, prospectively enrolled from January 2012 to November 2023 at 30 radiation oncology centers in a Michigan Radiation Oncology Quality Consortium (MROQC). Standardized patient, physician, and physicist forms were used to collect baseline and follow-up information. A severe toxicity composite variable included patient- or physician-reported breast pain or moist desquamation. Cosmesis scores were evaluated at 1 year. Multivariable models were used to find associations between boost and toxicity outcomes.

Clinical and treatment data were available for 11,753 women. A photon or electron boost was used in 49.0% and 22.1% of patients, respectively; 28.9% received no boost. The mean MH-WBRT dose to 95% of the volume was 40.6 Gy; median boost dose was 10 Gy/4 fractions. Both boost types were associated with greater composite acute toxicity, patient-reported breast pain, physician-reported breast pain, and grade 2+ dermatitis (P < .001). Fair/poor cosmesis was not associated with electron boost, though an association with photon boost cannot be excluded (odds ratio, 1.30; 95% CI, 1.00-1.68).

Using real world data, an electron or photon boost following MH-WBRT is associated with significantly more acute breast pain and dermatitis. Although there was no deleterious effect of an electron boost on cosmesis at 1 year, the impact of a photon boost is unclear. These data may help shared decision making when discussing the benefits and risks of a boost following MH-WBRT.