Should Stereotactic Radiosurgery Be Considered for Salvage of Intracranial Recurrence after Prophylactic Cranial Irradiation or Whole Brain Radiotherapy in Small Cell Lung Cancer? A Population-Based Analysis and Literature Review

Background: Prophylactic cranial irradiation (PCI) improves survival and prevents intracranial recurrence (IR) in limited stage (LS) and extensive stage (ES) small cell lung cancer (SCLC). However, despite PCI, IR affects 12%-45%, and limited data exist regarding salvage brain reirradiation (ReRT). We performed a population-based review of IR in SCLC. Methods: Demographic, treatment, and outcome data of consecutive patients (N = 371) with SCLC assessed at a tertiary cancer centre (01/2013-12/2015) were abstracted, and summary statistics calculated. Kaplan-Meier estimates and univariate and multivariate analysis (MVA) via the Cox proportional hazard model were performed. Results: Median age was 66.1 years, and 59.8% were Eastern Cooperative Oncology Group (ECOG) performance status 0-2. Median survival was 24 months (95% CI 18.3-29.7 months) for LS (N = 103) and 7 months (95% CI 6.1-7.9 months) for ES (N = 268). 72 of 103 patients with LS and 97 of 214 of those with ES received PCI. 54 of 268 ES presented with brain metastases (BM) of whom 46 of 54 received whole brain RT (WBRT). 18.9% (32/169) recurred post-PCI (13 LS; 19 ES) and 30.4% (14/46) recurred after WBRT. Of those who recurred/progressed after cranial RT, 56.5% (26/46) had <5 BM, 39.1% had no extracranial disease, and 50% were ECOG 0-2. In retrospect, 17 of 46 would have been candidates for salvage stereotactic radiosurgery: 13 post-PCI and 4 post-WBRT. Conclusions: This cohort challenges commonly held beliefs that IR is always diffuse, associated with clinical deterioration, and synchronous with systemic failure. Approximately 1 in 3 SCLC patients with IR after PCI or WBRT appear clinically appropriate for salvage stereotactic radiosurgery.