Centre-specific treatment and outcomes of patients with brain metastases treated with whole brain or stereotactic radiation therapy: an Ontario-based retrospective cohort study

Background: Whole brain radiation therapy (WBRT) and stereotactic radiation therapy (SRT) are the two most common treatments for patients with intracranial metastatic disease (IMD). In Ontario, Canada, 4 of the 18 (22%) regional cancer centres (RCC) are fitted with dedicated cranial SRT program, which we refer to as SRT-dedicated program centres, while the remaining RCCs deliver SRT but lack a dedicated cranial SRT program. We hypothesized that SRT usage would be higher and patient outcomes better in RCCs with vs. those without an SRT-dedicated program. Methods: Using administrative data housed at the Institute for Clinical Evaluative Sciences (IC/ES), we identified patients who had a primary cancer diagnosis and received cranial RT between April 1, 2010, and August 31, 2023. Treatment centres were grouped based on the presence or absence of an SRT-dedicated program. Within these groupings, hazard ratios (HR) for overall survival (OS) were compared. Additional comparisons based on the movement of patients across centres were performed. Results: The median OS of the cohort was 6.05 months. Significant differences in treatment and patient characteristics were observed according to RT modality used at RCCs with SRT-dedicated programs vs. those without, including the ratio of WBRT vs SRT (OR = 2.8, 95% CI 2.4-3.2, p < 0.0001), patient age (X^2 = 38.2, df = 7, p < 0.0001), stage at diagnosis (X^2=50.1, df = 4, p < 0.0001), and number of brain metastases treated (OR = 29.9, 95% CI 14.5-76.9, p < 0.0001). The median OS for patients treated with intracranial RT (WBRT or SRT) at centres with vs. those without a dedicated SRT programs was 7.20 vs 5.03 months (HR = 0.81, p < 0.0001), respectively. OS for patients who were treated with SRT at centres with vs. without a dedicated SRT program was 10.15 vs 7.89 months (HR = 0.88, p = 0.0275), respectively. No significant difference in the median OS for patients treated with WBRT at centres with or without a dedicated SRT program was observed (2.96 vs 3.09 months, HR = 1.08, p = 1.0, respectively). Mean OS for patients who travelled to a centre with a dedicated SRT program for intracranial RT after initial systemic therapy at a non-SRT-dedicated centre was associated with an positive impact on OS, compared to OS for patients who received systemic therapy and RT at a non-SRT-dedicated centre (14.0 vs 7.3 months, t = -3.9, p < 0.001). Conclusion: Our study found greater utilization of SRT and significantly longer OS for patients with IMD treated in Ontario RCCs with an SRT-dedicated program. OS was not negatively impacted for patients who travelled to a centre with a dedicated SRT program for radiation therapy.