123I-Meta-Iodobenzylguanidine Single-Photon Emission Computerized Tomography/Computerized Tomography Scintigraphy in the Management of Neuroblastoma

Abstract

Neuroblastoma is the most common pediatric extracranial solid tumor. High-risk neuroblastoma is the most frequent presentation with an overall survival of approximately 50%. ¹²³I-meta-iodobenzylguanidine (¹²³I-mIBG) scintigraphy in the assessment of the primary tumor and its metastases at diagnosis and after chemotherapy is a cornerstone imaging modality. In particular, the bulk of skeletal metastatic disease evaluated with ¹²³I-mIBG at diagnosis and the following chemotherapy has a prognostic value. Currently, single-photon emission computerized tomography/computerised tomography (SPECT/CT) is considered a fundamental part of ¹²³I-mIBG scintigraphy. ¹²³I-mIBG SPECT/CT is a highly specific and sensitive imaging biomarker and it has been the basis of all existing neuroblastoma trials requiring molecular imaging. The introduction of SPECT/CT has shown not only the heterogeneity of the mIBG uptake within the primary tumor but also the presence of completely mIBG nonavid metastatic lesions with mIBG-avid primary neuroblastomas. It is currently possible to semi-quantitatively assess tracer uptake with standardized uptake value, which allows a more precise evaluation of the tracer avidity and can help monitor chemotherapy response. The patchy mIBG uptake has consequences from a theranostic perspective and may partly explain the failure of some neuroblastomas to respond to ¹³¹I-mIBG molecular radiotherapy. Various positron emission tomography tracers, targeting different aspects of neuroblastoma cell biology, are being tested as possible alternatives to ¹²³I-mIBG.

Keywords: 123I-meta-iodobenzylguanidine scintigraphy; 123I-meta-iodobenzylguanidine single-photon emission computerized tomography/computerised tomography; high-risk neuroblastoma; standardised uptake value.

Figure 1

(a-f) 8-month-old girl with large neuroblastoma in the abdomen and pelvis at diagnosis. (c-f) ¹²³I-meta-iodobenzylguanidine scintigraphy with single-photon emission computerized tomography/computerized tomography clearly shows the heterogeneous meta-iodobenzylguanidine uptake of the primary tumor (blue arrows). (d) Expansile meta-iodobenzylguanidine nonavid lytic metastatic lesion in a left rib with a mildly avid small soft-tissue nodule adjacent to it (orange arrow). (a and f) Enlarged left para-aortic and retrocaval meta-iodobenzylguanidine-avid lymph nodes (yellow arrows)

Figure 2

¹²³I-meta-iodobenzylguanidine scintigraphy with single-photon emission computerized tomography/computerized tomography in a 4-year-old girl with relapsed neuroblastoma. The image shows a metastatic lesion at the base of skull, not identified on planar images, clearly visible with single-photon emission computerized tomography/computerized tomography sequence

Figure 3

(a-c)¹²³I-meta-iodobenzylguanidine single-photon emission computerized tomography with contrast-enhanced diagnostic quality computerized tomography after induction chemotherapy of a 4-year-old boy with stage M neuroblastoma. The meta-iodobenzylguanidine-avid primary tumor encases the right renal vessels (yellow arrow, b). Because of this imaging defined risk factor surgery was postponed and further chemotherapy was administered.

Figure 4

A 3-year-old boy with relapsed refractory neuroblastoma at different time points during follow-up. While no obvious change is visually identifiable on ¹²³I-meta-iodobenzylguanidine scintigraphy planar images, the evaluation of the standardized uptake value on the single-photon emission computerizedtomography/computerized tomography clearly shows a decreasing ¹²³I-meta-iodobenzylguanidine avidity of the primary tumor during treatment