Could 18F FDG PET/CT replace 131 I MIBG in the imaging of neuroblastoma?

Objectives To compare18F FDG PET/CT study to 131I-MIBG scintigraphy in staging, treatment response and restaging of Neuroblastoma patients.

Methods 50 diagnosed cases of neuroblastoma were subjected to F18 FDG PET/CT and I131-MIBG scan as a part of pre treatment evaluation. Similarly for treatment response -109 and in restaging cases- 15 paired scan were done. Both the scans were done within a time span of 10 days. The images were compared for concordance of uptake in the primary lesion, metastatic loco regional /distant nodes and distant metastases.

Results All the lesions noted on I-131 MIBG scans were also seen on F18 FDG response ET/CT scans. FDG scan revealed additional lesions in 50% (25/50) patients. Additional loco regional nodes were noted in 6 patients, supraclavicular nodes in 15 patients, marrow lesions in 5 patients and lung nodules in 4 patients. Peritoneal deposits and inferior temporal fossa deposits were other lesions seen on FDG scan but not seen on MIBG scan. In treatment response concordance of scan was noted in 67.8% (74/109) patients. Discordance was noted in 32.1% (35/109) patients. MIBG was better 17.4% (19/109) and PET better in 14.67% (16/109) patients. In restaging concordance was noted in 26.6% (4/15) and discordance was noted in 73.3% (11/15) and in all of them PET was better.

Conclusions F18 FDG PET/CT scan has a higher sensitivity and upstages 50 % cases. The poorer sensitivity of I131 MIBG may be due to the “TUMOR SINK EFFECT” and lower spatial resolution. Higher sensitivity, better spatial resolution, ease of availability and simultaneous morphological CT correlation make F18 FDG PET/CT scan a one stop shop for staging and restaging of Neuroblastoma. In treatment response complete response by FDG-PET metabolic evaluation did not always correlate with complete response by MIBG uptake as FDG PET/CT is metabolic imaging and MIBG is receptor imaging showing tumour viability.