Utilizing phenotypic characteristics of metastatic brain tumors to improve the probability of detecting circulating tumor DNA from cerebrospinal fluid in non-small-cell lung cancer patients: development and validation of a prediction model in a prospective cohort study

•Intracranial tumor size and distance to nearest ventricle were significantly correlated with positive CSF ctDNA detection.•A prediction model incorporating Tsize and LVDmin was developed and validated to evaluate the odds of CSF ctDNA positivity.•The CSF ctDNA detection rate was significantly improved in patients after model selection.