Abstract IntroductionPreoperative differential diagnosis between glioblastoma (GBM) and primary central nervous system lymphoma (PCNSL) is important because these tumors require different surgical strategies. This study investigated the usefulness of dual isotope, iodine-123-labeled N-isopropyl-p-iodoamphetamine (123I-IMP) and thallium-201 chloride single photon emission computed tomography (201Tl SPECT) for the differential diagnosis.MethodsTwenty-five PCNSL patients and 27 GBM patients who underwent dual isotope, 123I-IMP and 201Tl SPECT are included. Tumor to normal (T/N) ratio was calculated from the ratio of maximum tracer counts in the contrast-enhanced lesion to the mean counts in the contralateral cerebral cortex. The mean and minimum apparent diffusion coefficient values (ADCmean, and ADCmin, respectively) on magnetic resonance imaging were also analyzed. ResultsTumor to normal (T/N) ratios of PCNSL were significantly higher than that of GBM for both isotopes and phases (P < 0.001). Both ADC values of PCNSL were significantly lower than those of GBM (P < 0.001). Delayed phase 123I-IMP gave the most accurate findings for differentiation between PCNSL and GBM with the optimum cut-off value of 1.009, sensitivity 92.0%, specificity 88.9%, and area under the curve 0.945 (95% confidence interval, 0.883-1.000). Fifty of 52 patients (96.2%) showed retention index of 201Tl SPECT 0.7 or higher, which indicates malignant brain tumors. ConclusionsDelayed phase 123I-IMP SPECT could differentiate between PCNSL and GBM with the highest accuracy. 201Tl SPECT was useful for estimation of the malignancy and localization of the tumors. Dual isotope 123I-IMP and 201Tl SPECT was useful for the preoperative diagnosis of PCNSL and GBM.