MR Imaging Evaluation before Prophylactic Cranial Irradiation in Limited Stage Small Cell Lung Cancer: Prophylactic or Therapeutic?

Abstract

Prophylactic cranial irradiation (PCI) has an established role in limited stage (LS) small cell lung cancer (SCLC) for reduction of brain metastasis (BM) incidence and prolongation of survival. However, in practice, a considerable number of patients were found to have BM at the time of PCI, even if no BM were revealed by brain magnetic resonance imaging (MRI) with contrast at diagnosis and no central nervous system (CNS) symptoms existed. This study aims to clarify the role of brain MRI evaluation before PCI in LS-SCLC. Retrospective review of LS-SCLC in our institute from January, 2013 to July, 2018 was conducted. The enrolled criteria included the followings: 1) response evaluation was complete remission (CR) or partial remission (PR) after 4-6 cycles of chemotherapy with platinum - based regimen and thoracic irradiation. PCI was performed within 3 months after systemic management; 2) BM was excluded by cranial MRI with contrast at diagnosis; 3) before PCI, contrast-enhanced cranial MRI was performed. 236 patients were enrolled. 142 (60.2%) were male. The mean age was 55.8 years old. 37 patients (15.7%) were revealed to have BM (total numbers of BM lesions: 154) at this stage by cranial MRI with contrast. Among this population of BM, 28 (75.7%) individuals had no any symptoms and the BM lesions in 37.8% patients were invisible by simulation CT scan. The mean largest diameter of the BM lesions was 10.7mm. 63.6% of the BM foci detected were ≤10mm. The mean interval from diagnosis of SCLC (initiation of first chemotherapy) to BM was 201 days (range: 148-251d), during which brain MRI with an average of 2.3 times was performed. In LS-SCLC, the occurrence of BM should be highly alert pre-PCI , even for those patients without CNS symptoms. For this special entity, BM lesions tend to be small and undetectable by CT scan. Contrast-enhanced cranial MRI is strongly recommended for decision making of PCI or BM radiotherapy.