n.99 – RETROSPECTIVE ANALYSIS OF IMAGING WITH 123I-MIBG IN CHILDREN AFFECTED BY NEUROBLASTOMA: ADDED VALUE OF SPECT/CT COMPARED WITH DIAGNOSTIC CT



Abstract

BACKGROUND-AIM
Neuroblastoma is one of the most common childhood solid tumours. Among the imaging techniques available for diagnosis and follow-up of neuroblastoma (sonography, CT, MRI, and PET), the most commonly used today is CT with intravenously (IV) contrast material injection. Aim of the study was to evaluate the contribution of 123I-MIBG SPECT/CT to contrast-enhanced CT image analysis in the follow-up of patients (pts) with neuroblastoma in order to assess its impact on pts management.
METHODS
Our retrospective analysis included the imaging studies of 16 children (9 males and 7 females) with a mean age of 4 years (age range, 1 to 7 years); 13 of those suffered with neuroblastoma IV° and 3 with neuroblastoma III°. 9 scans were acquired for post-therapeutic evaluation (8 chemiotherapy and 1 131I-MIBG) and 7 scans for initial post-operation extension. Whole body planar imaging and SPECT/CT scans (Symbia T2, Siemens) of the anatomic region with a suspicious finding were acquired 24 hours after IV injection of 123I-MIBG (180 MBq, after thyroid blockage with Lugol 1%,). Whole Body scans were acquired at 159 keV with medium energy general purpose (MEGP) collimators; acquisition matrix and speed were equal to 256×1024 and 6 cm/min, respectively. SPECT imaging was composed of 64 projections of 40s and acquisition matrix equal to 128×128. The CT acquisition was a low-power X-ray transmission principally in order to assess the attenuation correction.
The analysis of the imaging was evaluated by using a program displaying superimposed slices of the same MIBG SPECT and CT level. All patients underwent a separate diagnostic contrast-enhanced CT in other hospitals. Retrospective analysis of MIBG SPECT/CT and diagnostic CT included assessment of concordance or discordance between SPECT/CT and contrast-enhanced CT, and all other available imaging or clinical information.
RESULTS
In 9/16 (56%) cases, SPECT/CT and contrast-enhanced CT showed concordance among them (5 pts presented only primary tumour, 2 pts had primary tumour and lymphonodal mts, 1 pt primary tumour and bone mts, 1 primary tumour and lymphonodal, hepatic and bone mts). In 7/16 (44%) cases 123I-MIBG SPECT/CT allowed to provide additional information to contrast-enhanced CT. In particular, SPECT/CT demonstrated pathological localizations of the radiotracer in sites (especially in proximal and distal diaphysis of long bones) that were not identified by the diagnostic contrast-enhanced CT.
Moreover, 123I MIBG SPECT/CT showed the real distribution of the radiotracer within the lesions: useful information in order to administer an eventual therapy with 131I-MIBG.
Finally, 123I-SPECT/CT MIBG demonstrated a better and early evaluation in the neo-adjuvant therapeutic response mostly at bone level but also of the main lesion in correlation with the clinical results.
CONCLUSION
The retrospective analysis of the imaging of our group of Neuroblastoma pts underlined that SPECT/CT (56% of pts) confirmed the results of the diagnostic CT. In 44 % of the cases, it allowed to mark out the presence of pathological uptake and the characterization of its findings that were not diagnosed by CT. Hence, the information from 123I-MIBG SPECT/CT are crucial for early detection of relapse, the impact on treatment and finally, the prognosis of Neuroblastoma disease.

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