The quarterly journal of nuclear medicine : official publication of the Italian Association of Nuclear Medicine (AIMN) [and] the International Association of Radiopharmacology (IAR)
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The avidity of many metastatic pheochromocytomas and neuroblastomas for metaiodobenzylguanidine (MIBG) observed at diagnostic scintigraphy has led to attempts to treat these lesions with large doses of MIBG. We and others have achieved therapeutic responses with 131I-MIBG (usually partial) in about a third of malignant pheochromocytomas. ⋯ This has led to prolonged tumor stabilization and survival (> 19 to > 52 months) in 5 of 10 patients. MIBG radiopharmaceutical treatment of neuroendocrine tumor patients must still be considered an experimental but nevertheless promising treatment modality.
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Comparative Study
In vitro and in vivo studies with no-carrier added radioiodinated MIBG.
An important drawback of radioiodinated MIBG prepared by isotopic exchange (maximum specific activity: 100 Ci/mmol) is that a considerable amount of carrier is present in the "ready to use" radiopharmaceutical, thus affecting MIBG uptake in the target cells. To improve the therapeutic utility of MIBG an interesting method was developed for the no-carrier-added (n.c.a.) radioiodination of MIBG via a halodesilylation reaction using 3-trimethylsilybenzylguanidine (TMSBG) as precursor. In order to investigate its possible clinical usefulness, n.c.a. [125I]- and [131I]MIBG was prepared according this procedure. ⋯ MIBG uptake was also studied in the human neuroblastoma cell line SH-SY5Y which has a specific uptake system for MIBG. The kinetic parameters for MIBG in this line are: km = 0.27 +/- 0.03 microM, Vmax = 39.5 + 1.8 pmol/10(6) cell/10 min. Preliminary data from in vitro binding studies showed that significantly higher levels of specifically incorporated radioactivity can be achieved using n.c.a. [125I]MIBG instead of c.a. [125I]MIBG.
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In a group of 97 patients aged from 6 months to 12 years, all with suspected or proven neural crest tumours, metaiodobenzylguanidine (MIBG) scintigraphy was performed at the time of diagnosis and, in some instances, after induction chemotherapy. All the patients underwent a tumour biopsy with cytological and histological analysis, in addition to imaging examinations such as X-rays, ultrasound, computed tomography and magnetic resonance, within a short period before or after scintigraphy. In 82 of 97 cases MIBG was effective in detecting the primary tumour, hence the technique's sensitivity was 84%. ⋯ Out of 12 cases showing metastases at diagnosis, two cases with liver lesions became normal and in one case some, but not all, of the bone lesions were not detectable; 4 cases remained abnormal, while in 5 cases bone marrow involvement was not confirmed. Three cases were confirmed to be true negatives; in 4 other cases bone marrow involved not showing at diagnosis was revealed and confirmed by biopsy; 3 cases in which bone marrow involvement was not revealed by MIBG at diagnosis, had normal MIBG and biopsy results after IC; finally, 2 false negative bone marrow cases and 5 true negative cases at diagnosis remained unchanged, but were not checked by biopsy. Performing total body MIBG scintigraphy in childhood neuroblastoma at diagnosis is useful: 1) to predict the nature of the masses detected by other imaging techniques, when biopsy has not yet been performed; 2) for more accurate tumour staging, in addition to standard imaging investigations, MDP scintigraphy and bone marrow aspiration biopsy, thanks to its ability to detect metastatic lesions; 3) to anticipate the decrease in sensitivity of the technique in detecting both the primary mass and the metastases following induction chemotherapy.