Other Tracers

Gallium-67 is rarely used for imaging of NB. Although nearly 80% sensitivity for detection of the primary tumor has been reported, gallium imaging did not visualize skeletal involvement (Garty et al. 1989). Tl-201 has been useful for imaging a variety of soft tissue tumors, but this tracer localizes poorly in NB (Howman-Giles et al. 1995). A number of ligands similar to MIBG have also been used to study sympathetic innervation of the heart as well as to image neuroendocrine tumors. These include I-123 amino iodobenzylguanidine (AIBG), F-18 fluorodopamine,

Figure 10.2

A 4-year-old with extensively treated neuroblastoma under consideration for bone marrow transplant. I-123 MIBG scan (not shown) showed no abnormal uptake. Left panel: Coronal image from PET-FDG scan shows large area of markedly increased uptake (arrow).Trans-verse image from PET-FDG scan (right upper panel) shows markedly increased uptake (arrow) occupying most of the abdomen.A CT scan of same area (right lower panel) shows the large abdominal mass (arrow) with mixed attenuation characteristics. The patient soon after died from progressive disease

F-18 fluronorepinephrine, F-18 fluorometaraminol, C-11 hydroxyephedrine (HED), C-11 epinephrine (EPI), C-11 phenylephrine, and fluoro-metaiodoben-zylguanidine (FIBG); only three have been investigated in patients with neuroendocrine tumors (Shulkin et al. 1986, 1996,1999). FIBG has been shown to be concentrated by NB cells in culture (Vaidynathan et al. 1994b). Benzylguanidine labeled with the alpha particle emitter Astatine 211 has been proposed as a potential radiotherapeutic agent (Vaidyanathan et al. 1994a). These derivatives of MIBG rely on the type-1 uptake pathway for entry into the cell.

The I-131 labeled monoclonal antibody 3F8 specific for ganglioside GD2 has been used for radioim-munoscintigraphy and radioimmunotherapy of NB. Because of the abundance of this antigen on neuroblastoma (5-10X10-6 molecules per cell), high levels of radiolabel can be deposited selectively to tumor instead of normal tissues (Miraldi et al. 1986; Yeh et al. 1991). The I-124 labeled form has also been used to improve tumor dosimetry (Larson et al. 1992). Several other monoclonal antibodies that may prove to be useful in imaging NB are under investigation (see Chap. 14 for a detailed discussion of antibody-based radioimmunotherapy).

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