Patterns of brain metastasis immediately before prophylactic cranial irradiation (PCI): implications for PCI optimization in limited-stage small cell lung cancer

Background: Prophylactic cranial irradiation (PCI) is indicated for limited-stage small cell lung cancer (LS-SCLC) with good response to chemoradiotherapy (CRT). However, brain metastasis (BM) developed in LS-SCLC before PCI is not rare. In this study, we comprehensively investigated the features of pre-PCI BMs, aiming to explore the potential of PCI optimization for LS-SCLC.

Methods: One-hundred-ten LS-SCLC patients achieving clinical complete remission after definitive CRT with contrast-enhanced cranial magnetic resonance imaging (MRI) at baseline and immediately before PCI were included. The time trend and risk factors for pre-PCI BM were evaluated. Several radiological features, including numbers, sizes, and locations of pre-PCI BMs, were investigated to explore the technical feasibility of stereotactic radiotherapy and hippocampal-avoidance (HA) PCI.

Results: Twenty-four (21.8%) of the LS-SCLC patients harbored pre-PCI BM, all except one were asymptomatic. CRT duration (CRT-D) was the only independent risk factor for pre-PCI BM. The pre-PCI BM rate gradually increased in line with a growing time interval between treatment initiation and pre-PCI MRI. Pre-PCI BM and prolonged CRT-D were both correlated with worse overall survival. Of 129 pre-PCI intracranial lesions, 2 (1.5%) were in the HA region. Eight of the 24 (33.3%) pre-PCI BM patients were ineligible for stereotactic radiotherapy.

Conclusion: Our findings suggest that PCI is still of importance in LS-SCLC, and MRI evaluation before PCI is indispensable. Investigations are warranted to explore the possibility of moving PCI up to before CRT completion in LS-SCLC patients with prolonged CRT-D. HA-PCI could be considered to reduce neurotoxicity.