124I-Metaiodobenzylguanidine (MIBG) PET/CT Diagnostic Imaging and Dosimetry for Patients With Neuroblastoma: A Pilot Study

This is a pilot study with the primary purpose to describe organ dosimetry and acute toxicities using no carrier added and carrier added 124I-MIBG PET/CT in patients with neuroblastoma (NB). Eligible patients are 3 years of age and older with relapsed or refractory neuroblastoma who are currently enrolled on a treatment protocol with 131I-MIBG. After all eligibility criteria are met, patients will receive a diagnostic imaging dose of 124I-MIBG followed by sequential PET/CT dosimetry scans on Days 0, 1, 2 and 5. Subsequent, planned therapeutic administration of 131I-MIBG will occur between Days 7 to 21, as specified by the patient's therapeutic MIBG protocol. An optional single follow up 124I-MIBG PET-CT scan will be done to assess tumor sites 6 weeks after the patient has their MIBG therapy.

Accurate radiation dose evaluation is important in patients with malignant tumors, and this is especially critical in children with NB who will be receiving several dose of therapeutic 131I. The accurate quantification of the isotope-labeled analog can only be achieved by using positron emission compounds, such as 124I. Unlike planar images, which were used to obtain kinetic information, and SPECT reconstruction modalities that were aimed to assess the spatial distribution of radioactivity, 3D PET imaging-based dosimetry is a method which provides a more accurate estimation of the cumulated radioactivity distribution. Because PET provides better quantitative accuracy, when compared to SPECT regarding the tissue absorbed information, we hypothesize PET would better correspond with tumor response and normal organ toxicity. Early studies using I-124 for dosimetry in thyroid cancer have been promising.

Demonstration of the feasibility and accuracy of this new imaging modality, with the excellent prospect for more accurate dosimetry, will improve tumor localization and optimize therapeutic dosing with 131I-MIBG. The results of our work may potentially have also implications in the study of other neuroendocrine tumors. The Section of Nuclear Medicine and the Laboratory of Functional Imaging at the University of California, San Francisco, are equipped with state of the art instruments and is run by a highly skilled staff which will guarantee the success of the proposed research.