Annual Brain MRI Surveillance for Detection of Brain Metastasis in Patients With Lung Cancer

This retrospective observational study will evaluate the effectiveness of periodic brain magnetic resonance imaging surveillance for detecting brain metastasis in patients with lung cancer. Using linked nationwide claims and cancer registry data from Korea, the study will emulate a sequence of monthly target trials among patients with newly diagnosed lung cancer and no prior brain metastasis. At each monthly trial, eligible patients will be classified according to whether they receive active brain MRI surveillance or remain in an inactive surveillance state. The main analysis will define the active surveillance period as one year after brain MRI. A sensitivity analysis will define the active surveillance period as two years. Patients may re-enter later trials if they again become eligible. Patients will be excluded from a given trial if they have recent neurologic symptoms suggesting diagnostic MRI, prior brain MRI within the preceding surveillance interval, brain metastasis, or death. The primary objective is to assess whether annual brain MRI surveillance increases detection of brain metastasis. Secondary objectives are to evaluate whether surveillance-detected brain metastases are more likely to be asymptomatic or potentially treatable, and whether surveillance-detected brain metastasis is associated with lower mortality among patients who develop brain metastasis.

Inclusion Criteria: \- Patients will be eligible if they have newly diagnosed lung cancer between 2012 and 2021 Exclusion Criteria: * Prior brain MRI within the preceding within 1 year * Incident brain metastasis before trial entry. * Recent neurologic symptoms, emergency department use, hospital admission, neurologic consultation, or prescriptions for dexamethasone, mannitol, levetiracetam, or valproate within prespecified time windows around the MRI date.