Addition of (131)I-MIBG to PRRT ((90)Y-DOTATOC) for Personalized Treatment of Selected Patients with Neuroendocrine Tumors

Peptide receptor radionuclide therapy (PRRT) is an effective treatment for metastatic neuroendocrine tumors. Delivering a sufficient tumor radiation dose remains challenging because of critical-organ dose limitations. Adding (131)I-metaiodobenzylguanidine ((131)I-MIBG) to PRRT may be advantageous in this regard. Methods: A phase 1 clinical trial was initiated for patients with nonoperable progressive neuroendocrine tumors using a combination of (90)Y-DOTATOC plus (131)I-MIBG. Treatment cohorts were defined by radiation dose limits to the kidneys and the bone marrow. Subject-specific dosimetry was used to determine the administered activity levels. Results: The first cohort treated subjects to a dose limit of 1,900 cGy to the kidneys and 150 cGy to the marrow. No dose-limiting toxicities were observed. Tumor dosimetry estimates demonstrated an expected dose increase of 34%–83% using combination therapy as opposed to (90)Y-DOTATOC PRRT alone. Conclusion: These findings demonstrate the feasibility of using organ dose for a phase 1 escalation design and suggest the safety of using (90)Y-DOTATOC and (131)I-MIBG.