Diagnostic accuracy of 201Thallium-SPECT and 18F-FDG-PET in the clinical assessment of glioma recurrence Manuel Gómez-Río & Antonio Rodríguez-Fernández & Carlos Ramos-Font & Escarlata López-Ramírez & José Manuel Llamas-Elvira JOURNAL CLUB PRESENTER KUMAR

This study aimed to test the hypothesis that incorporation of 18-fluoro-deoxy-glucose positron emission tomography (FDG-PET) increases the accuracy of this differential diagnosis obtained with 201Tl chloride- singlephoton emission computed tomography (201Tl-SPECT Seventy-six patients (mean age47.72±16.19 years) under suspicion of glioma recurrence,42% with low-grade and 58% with high-grade lesions, were studied by 201Tl- SPECT and FDG-PET,

Materials and methods prospective cohort study at neuro-oncology reference centre between March 2002 and March 2005 for suspicion of tumour recurrence. Clinical management of patients with glial tumour (WHO classification is established by the hospital Brain Tumours and Radio surgery Committee Tumour progression is defined according to McDonalds, based on both clinical (unequivocal relapse of neurological status after progression-free interval of >3 months) and MRI (appearance of new enhancing abnormalities or enlargement of enhanced zone in posttreatmentgliosis area) criteria. When examinations yield inconclusive results or suggest tumour recurrence, the patient is referred to NM Department for 201Tl-SPECTand FDG-PET examinations on the same day

Materials and methods MRI was performed using an 0.5 Tesla General Electric with and without Gadolinium. Images were analyzed byneuroradiology specialists, who focused on the appearanceof new enhancing abnormalities and enlargement of enhanced zone in posttreatment gliosis area SPECT All patients were examined within 15 min of the i.v. injection of 3–5 mCi 201Tl chloride. Images were acquired using a Triple Head Camera (Prism 3000; Picker-International) Significantly higher 201Tl uptake was considered postive. PET All patients fasted for ≥6 h before tracer injection and had a blood glucose concentration <120 mg/dl at the examination. A standard i.v. (weight-independent) dose of 185 MBqwas administered using a Siemens ECAT EXAT 47 PET tomograph.Examinations were considered positive if unexplainable metabolic activity was observed demonstrated by increased FDG uptake relative to immediately adjacent tissue

Assessment of diagnostic accuracy The gold standard for tumour recurrence was based on histological confirmation, recurrence was considered absent if patient was clinically stable and showed no MRI changes during >3 months for high-grade and >6 months for low- grade lesions The significance of differences in results among procedures was analyzed using the Mc Nemar test for paired samples..

Assessment of diagnostic accuracy

Results The mean follow-up period for our study cohort was 2.6 years The 76 patients studied had a mean age of 47.7 years (SD=16.2) and 57% were males. Histology of the primary lesion is exposed in 32 tumours (42.10%) were low-grade gliomas, and the remaining 44 were high-grade gliomas. During the study period, three of the low-grade diffuse astrocytomas (G-II) converted to high-grade forms. The prevalence of tumour recurrence (72.4%) was similar between low- (62.5%) and high- grade (79.5%) lesions. No diagnostic errors were observed in the subgroup of patients with histological confirmation (23 in our series),with tumour recurrence confirmed in all cases. Table 2 shows the internal and external accuracy parameters and values estimated for the whole cohort and for each

Results subgroup (patients with low or high-grade tumours).Sensitivity values were similar among the whole cohort and subgroups, with 201Tl-SPECT + MRI always showing higher sensitivity (>95% in cohort and subgroups) vs FDGPET (70 and 83% in low-grade and high-grade subgroups,respectively). In the high-grade subgroup, specificity was 100% for all procedures, with no false-positive examinations. In the low-grade subgroup, specificity values for 201Tl-SPECT, 201Tl-SPECT + MRI and FDG-PET were 75,83 and 92%, respectively. Accordingly, the likelihood ratio for a positive result was always higher with FDG-PET Conversely, the likelihood ratio for a negative result was lower with 201Tl-SPECT + MRI (0.04)

Discussion FDG-PET did not prove to be clearly superior to 201Tl- SPECT (with or without MRI) for the clinical diagnosis of glial tumour recurrence, The specificity and positive predictive value of FDG-PET were slightly higher, but its sensitivity and negative predictive value were appreciably lower. Hence, it appears that FDG-PET is slightly better for confirming tumour recurrence 201Tl-SPECT is better for ruling out a possible recurrence, which was detected in 38% of FDGPET negative explorations.

AdvantagesLimitations good quality cohort study prospective Cohort study with reasonable follow-up reporting results under blinded conditions using visual analysis. All images were analysed by Neuroradiologist Good reference standards had been used Methodological biases: Two different gold standard procedures, especially the follow-up There were interpretational error during radiological analysis Reference standards might vary with imaging tool hence applicability can be questionable Not a multicenter research criteria to be established for FDG- PET, 201Tl-SPECT, MRI and combinations of these examinations

WHAT IS ALREADY KNOWN ON THIS TOPIC Background: TCS may complement CT and MRI in the postoperative follow-up of patients with high-grade gliomas. Because none of these modalities alone is both sensitive and specific, an integrated analysis of imaging findings is useful. Neurosurgery Mar;44(3):469-77; discussion (201)Tl-SPECT is a valuable and noninvasive diagnostic procedure to detect recurrence or progression disease for treated gliomas and ependymomas. (201)Tl-SPECT has a good correlation with short term prognosis with excellent diagnostic accuracy. Clin Transl Oncol Oct;8(10): The inclusion of diffusion-weighted sequences in postoperative MR imaging is essential, as is MR imaging immediately before radiation therapy to monitor disease progression. J Neurosurg Sep;103(3):428-38

WHAT THIS STUDY ADDS 201Tl-SPECT should remain as a routine clinical procedure for the diagnosis of glioma recurrence. In high-grade lesions 201Tl-SPECT data had been useful & MRI did not add In Low-grade lesions MRI appears to be useful to establish the physiologic structures that take up Tl- 201 FDG-PET did not prove to be clearly superior to 201Tl-SPECT (with or without MRI) for the clinical diagnosis of glial tumour recurrence

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