Assessing the intracranial metabolic score as a novel prognostic tool in immunocompetent primary CNS lymphoma patients with end-of-treatment 18F-FDG PET/CT and PET/MR

Abstract Background The metabolic response of primary central nervous system lymphoma (PCNSL) patients has yet to be evaluated, and Deauville scoring (DS) is not suitable for brain PET/MR. This study aimed to assess the prognostic value of a novel scoring scale, the intracranial metabolic score (IMS), in PCNSL patients receiving end-of-treatment 18F-FDG PET/CT (EOT-PCT) and PET/MR (EOT-PMR). Methods The IMS was determined based on the metabolism of normal intracranial structures, including gray matter, white matter, and cerebrospinal fluid. The EOT-PCT cohort was evaluated using the IMS and DS. Another cohort of patients who underwent surgery via the EOT-PMR was used to validate the accuracy of the IMS. Results In total, 38 patients were enrolled in the PET/CT cohort, while 45 patients were enrolled in the PET/MR cohort. The area under the curve (AUC) values of the IMS for predicting 3-year PFS and 3-year OS were superior to those of the DS. When patients in the PET/CT cohort were stratified into five groups (respectively labeled IMS 1–5), three groups (IMS1-2, IMS 3–4, and IMS 5), or two groups (IMS1-3 and IMS4-5; IMS 1–4 and IMS 5), a higher IMS score was significantly correlated with poorer PFS and OS (p < 0.001). Similar results were observed for PFS in the PET/MR cohort (p < 0.001). The IMS and DS scale were found to be independent prognostic indicators for PFS and OS in the PET/CT cohort, and the IMS was identified as the sole independent prognostic indicator for PFS in the PET/MR cohort. Conclusion The IMS as a novel and effective prognostic tool for PCNSL patients, showing superior predictive value for patient outcomes compared to the DS when assessed with EOT-PET scans.