Radiation Therapy Infrastructure, Social Vulnerability, and Insurance Architecture Predict Timely Postoperative Radiation Therapy After Brain Tumor Craniotomy.

Purpose: Timely initiation of radiation therapy (RT) following craniotomy for malignant brain tumors is associated with better clinical outcomes. Despite guideline recommendations and best practices, the timely initiation of postoperative RT remains suboptimal. Our objective was to evaluate how structural, social, and payer-related factors independently and interactively influence RT initiation following craniotomy. Methods and Materials: We conducted a retrospective, patient-level cohort study using a large, linked, multisource data set that incorporated all-payer claims from 2023, geospatial hospital data, and indicators of community vulnerability. RT initiation was assessed at 42-, 60-, and 90-day postoperative intervals. Primary predictors included hospital referral region-level RT center density, hospital proximity, payer type, and Centers for Disease Control and Prevention/Agency for Toxic Substance and Disease Registry (CDC/ATSDR) Social Vulnerability Index (SVI) domains. Secondary analyses included region and hospital type. Results: Among 18,885 patients across 548 hospitals, 29.2% initiated RT ≤ 42 days, 45.6% ≤ 60 days, and 48.9% ≤ 90 days. Hospital-level RT initiation ≤42 days ranged from 0% to 87.5%. Hospital referral region per capita RT center density was the strongest structural predictor of RT initiation ≤42 days (adjusted odds ratio [aOR] per IQR, 1.18; 95% CI, 1.11-1.25) and lower odds of noninitiation ≤90 days (aOR, 0.84; 95% CI, 0.78-0.90). Hospital proximity predicted RT initiation ≤42 days (aOR, 1.12; 95% CI, 1.08-1.17) but not ≤90 days. Medicaid coverage predicted lower odds of RT initiation ≤42 days (aOR, 0.58) and higher odds of noninitiation ≤90 days (aOR, 2.29); Medicare coverage predicted lower odds of timely initiation but not of noninitiation (aOR, 0.76). Higher community social vulnerability (Social Vulnerability Index), particularly the share of elderly residents, limited transportation, and housing cost burden, predicted noninitiation, with interaction models showing that hospital density mitigated, but did not eliminate, these disadvantages. Conclusions: Structural access, socioeconomic disadvantage, and insurance coverage independently and interactively predict the timely initiation of postoperative RT, with greater regional RT capacity improving initiation but not fully mitigating social and payer-related barriers.