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.