Abstract
1384
Objectives F-18 fluorodeoxyglucose (FDG) is increasingly used monitoring tumor response. High dose I-131 metaiodobenzylguanidine (MIBG) radiotherapy (12mCi/kg) has shown slightly improved outcome in patients with malignant pheochromocytoma (PHEO) and paraganglioma (PGL). However, the high dose MIBG therapy increases toxicity. Thus, alternative therapeutic options are required. The purpose of this study was to evaluate the effects of repeated MIBG radiotherapy on tumor size and metabolic activity in patients with metastatic PHEO and PGL.
Methods Eight patients with metastatic PHEO or PGL (age 51±11years) were prospectively treated with I-131 MIBG and the total 22 MIBG therapies were performed. These patients repeated 150 mCi of MIBG therapy within 6 months intervals. Mean treatments were 2.8 ±0.4 times and mean cumulative MIBG dose was 412.5±65.0 mCi (7.5mCi/kg). The tumor responses by computed tomography (CT), and FDG PET or PET/CT were observed before and after the MIBG treatment. FDG uptake was evaluated visually using 5 point scoring scale (greater than 4 was defined positive).
Results Three patients showed partial remission and 5 patients were stable based on CT findings with RECIST criteria. However, no patient showed progressive disease. Sum longest diameter did not change after MIBG therapy (259.4±258.0 vs 216.1±258.0 mm, ns) in patient based analysis. In tumor region based analysis, MIBG therapy significantly reduced FDG uptake score (N=90; 4.49±1.04 vs 3.47±1.68, P<0.0001). MIBG therapy significantly reduced numbers of FDG positive regions (N=90, 85.6% to 56.7%, P<0.01).
Conclusions Repeated MIBG therapy reduced tumor metabolic activity both in partial response or stable disease population. Therefore, relatively short period of repeated MIBG treatment might be one of the therapeutic options for reducing tumor metabolic activity in patients with metastatic pheochromocytoma or paraganglioma.