RT Journal Article SR Electronic T1 Effects of Repeated 131I-meta-iodobenzylguanidine Radiotherapy on Tumor Size and Tumor Metabolic Activities in Patients with Metastatic Neuroendocrine Tumors JF Journal of Nuclear Medicine JO J Nucl Med FD Society of Nuclear Medicine SP jnumed.120.250803 DO 10.2967/jnumed.120.250803 A1 Keiichiro Yoshinaga A1 Takashige Abe A1 Shozo Okamoto A1 Yuko Uchiyama A1 Osamu Manabe A1 Yoichi M. Ito A1 Naomi Tamura A1 Natsue Ito A1 Naho Yoshioka A1 Komei Washino A1 Nobuo Shinohara A1 Nagara Tamaki A1 Tohru Shiga YR 2020 UL http://jnm.snmjournals.org/content/early/2020/10/16/jnumed.120.250803.abstract AB 131I-meta-iodobenzylguanidine (131I-MIBG) radiotherapy has shown some survival benefits in metastatic neuroendocrine tumors (NETs). European Association of Nuclear Medicine (EANM) clinical guidelines for 131I-MIBG radiotherapy suggest a repeated treatment protocol, although none currently exists. The existing single-high-dose 131I-MIBG radiotherapy (444 MBq/kg) has been shown to have some benefits for patients with metastatic NETs. However, this protocol increases adverse effects and it requires alternative therapeutic approaches. Therefore, the aim of this study was to evaluate the effects of repeated 131I-MIBG therapy on tumor size and tumor metabolic response in patients with metastatic NETs. Methods: Eleven patients with metastatic NETs (age 49.2±16.3) prospectively had repeated 5550 MBq of 131I-MIBG therapy within 6-month intervals. A total of 31 treatments were performed. Mean treatments were 2.8 ± 0.4 times and cumulative 131I-MIBG dose was 15640.9 ±2245.1 MBq (286.01 MBq/kg). The tumor responses were observed by computed tomography (CT), 18F-FDG PET or PET/CT before and 3 to 6 months after the final 131I-MIBG treatment. Results: Based on CT findings with Response Evaluation Criteria in Solid Tumors (RECIST) criteria, 3 patients showed a partial response (PR) and 6 patients showed stable disease (StaD). The remaining 2 patients showed progressive disease (PD). Although there were 2 PD patients, analysis of all patients showed that there was no increase in sum longest diameter (SLD) [228.7 (37.0-336.0) to 171.0 (38.0-270.0) mm, P = 0.563]. In tumor region-based analysis with PR and StaD patients ( n = 9), 131I-MIBG therapy significantly reduced tumor diameter [n = 79 lesions, 16 (12-22) to 11 (6-16) mm, P< 0.001). Among 5 patients with hypertension, there was a strong trend in systolic blood pressure (BP) reduction, (P= 0.058) and diastolic BP was significantly reduced (P= 0.006). Conclusion: Eighty-two percent of metastatic NETs patients effectively achieved disease progression inhibition with reduced tumor size and metabolic activity through repeated 131I-MIBG therapy. Therefore, this relatively short-term repeated 131I-MIBG treatment may have potential as one option in a therapeutic protocol for metastatic NETs. Larger prospective studies with control groups are warranted.