NIMG-34. 99MTC-MIBI SINGLE PHOTON EMISSION COMPUTED TOMOGRAPHY-COMPUTED TOMOGRAPHY (SPECT-CT) TO DETECT TUMOR PROGRESSION IN GLIOBLASTOMAS (GB)

Post-treatment assessment of primary brain tumors presents a diagnostic challenge to distinguish real tumor progression (PD) from pseudoprogression or radiation necrosis (PsP/RN). Brain MRI, the gold standard imaging modality is often misleading, even when adding functional sequences (perfusion and/or spectroscopy). SPECT-CT (99mTc-MIBI SPECT with CT) might add complimentary data to MRI in this regard, merging the molecular imaging capabilities of SPECT with more accurate morphologic data from CT images in one single exam. This retrospective study included consecutive patients (pts) treated for glioblastomas (GB) in our institution that had at least one MIBI for suspected PD. Main objective was to assess MIBI early uptake performance in differentiating PD from PsP/RN. PD is defined as unequivocal active tumor on surgical resection/biopsy specimens when available, and/or clinical/radiological PD in the ensuing three months following the MIBI. Uptake in the suspected area was calculated relatively to uptake in the contralateral normal brain. The primary outcomes are sensitivity (Sn), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV), and accuracy (A), based on the ROC curve generated from early uptake data against outcome. We included 27 pts, comprising of 30 independent observations (3 pts underwent repeated MIBIs for suspected PD in two distinct occasions). 19 males and 8 females, median age of 50 years (range 25 to 70). The ROC curve identified 4.2 as the most appropriate cut-off value for early uptake (Youden´s Index 0,62). With this, MIBI reached 91,3% Sn, 71,4% Sp, 91,3% PPV, 71,4% NPV and 86,7% A. MIBI seems to be an accurate and inexpensive imaging modality to assess in glioblastomas. We plan to do a prospective study evaluating MIBI in this setting in GB.