Boost delivery in hypofractionated breast cancer radiotherapy: A registry-based analysis of treatment patterns and survival.

Hypofractionated radiotherapy (RT) has become standard in breast cancer treatment; however, the factors guiding boost application and its impact on survival remain uncertain. In the present study, predictors of boost application and its association with survival were analyzed. A registry-based analysis of n=3,411 patients with breast cancer treated with hypofractionated RT, including 40 post-mastectomy cases, was conducted; n=1,366 patients received a boost. Predictors of boost administration were assessed using uni- and multivariate logistic regression, and overall survival (OS) was examined using Cox hazards models, including subgroup analyses stratified by boost RT, with missing data addressed using complete-case and multiple imputation approaches. The median age was 62 years (interquartile range, 54-70 years). Younger age [odds ratio (OR), 0.96 per year; 95% CI, 0.95-0.97], higher T-stage (T2; OR, 2.54; 95% CI, 1.86-3.48), positive HER2 status (OR, 1.85; 95% CI, 1.31-2.61) and RT target volume (whole-breast irradiation) predicted boost administration. Higher T-stage [T2: hazard ratio (HR), 1.72; 95% CI, 1.04-2.84; T3+: HR, 4.26; 95% CI, 1.55-11.7] and older age (HR, 1.06 per year; 95% CI, 1.04-1.09) were associated with worse OS, while positive progesterone receptor (PR) status predicted improved OS (HR, 0.46; 95% CI, 0.23-0.90). Boost administration exhibited no significant impact (HR, 0.98; 95% CI, 0.60-1.58). In this registry-based cohort, younger age, higher T-stage, positive HER2 status and RT target region independently predicted boost administration. While higher T-stage, older age and PR negativity were associated with worse OS, boost administration itself had no significant impact.