NI-2 DUAL-ISOTOPE 123I-IMP/201TL SPECT FOR THE DIFFERENTIAL DIAGNOSIS OF PRIMARY CENTRAL NERVOUS SYSTEM LYMPHOMA AND GLIOBLASTOMA

BACKGROUND: Preoperative differential diagnosis between primary central nervous system lymphoma (PCNSL) and glioblastoma (GBM) is important because these tumors require different surgical strategies. This study investigated the usefulness of dual isotope, iodine-123-labeled N-isopropyl-p-iodoamphetamine ((123)I-IMP) and thallium-201 chloride single photon emission computed tomography ((201)Tl SPECT) for the differential diagnosis. METHODS: Sixteen PCNSL patients and 20 GBM patients who underwent dual isotope imaging, (123)I-IMP and (201)Tl SPECT, are included. Early and delayed SPECT images were obtained after 30 minutes and 4 hours, respectively. Tumor to normal (T/N) ratio was calculated from the ratio of maximum tracer counts in the lesion to the mean counts in the contralateral cerebral cortex. The mean and minimum apparent diffusion coefficient values (ADC(mean) and ADC(min), respectively) on magnetic resonance imaging were also analyzed for comparison of diagnostic accuracy. RESULTS: Delayed phase (123)I-IMP SPECT was the most useful imaging examination for the differentiation between PCNSL and GBM compared with early phase (123)I-IMP SPECT, early and delayed phase (201)Tl SPECT, ADC(mean) and ADC(min). However, the median T/N ratios of PCNSL and GBM were 1.29 and 0.84, respectively, in the delayed phase (123)I-IMP SPECT, and the tumor detection was inadequate. On the other hand, the median T/N ratios of PCNSL and GBM were 3.23 and 2.34, respectively, in the delayed phase (201)Tl SPECT, with excellent tumor detection. Thirty-five of 36 patients (97.2%) showed a tracer retention rate of (201)Tl SPECT 0.7 or higher, which indicates malignant property of brain tumors. CONCLUSION: Delayed phase (123)I-IMP SPECT could differentiate between PCNSL and GBM with high accuracy, but T/N ratio was low and tumor detection was poor. (201)Tl SPECT was useful for estimation of the localization and the malignant property of the tumors. The combination of these isotopes was useful for the diagnosis of PCNSL and GBM.