Prospective Comparison of 18F-FDG and 18F-FET PET for Response Evaluation in Patients With Primary Central Nervous System Lymphoma

Inclusion Criteria: In order to be eligible for participation in this trial, the subject must: * Be ≥ 19 years of age. * Patients diagnosed with central nervous system lymphoma by surgery/biopsy or suspected of central nervous system lymphoma by anatomical imaging examination such as MRI. * Patients who have results or are planning to examine 18F-FDG PET in the above patients. Exclusion Criteria: The subject must be excluded from participating in the trial if the subject fulfil any single criteria described below: * Pediatric and adolescent patients under 19 years of age. * The patient is pregnant, is attempting to become pregnant, or is nursing (breast-feeding) to children. * Patients with diagnosed or suspected lymphoma lesions in organs other than the cetral nervous system. * Based on the investigator's judgement, if the patient makes it impossible to collect complete data for a clinical trial due to personal or other reasons. * Patients who cannot stably have PET/CT due to claustrophobia, dyskinesia, anxiety disorder, seizure, etc. * Based on the investigator's judgement, if the patient has a serious and/or uncontrolled and/or unstable medical disease (e.g., congestive heart failure, acute myocardial infarction, severe lung disease, chronic renal disease or chronic liver disease, etc.)