Using 131I metaiodobenzylguanidine (MIBG) to image cases of pediatric neuroblastoma is not a new concept, whether the radiotracer is intended for initial diagnosis or for following up on chemotherapy. Nearly 20 years ago, a report in the Journal of Nuclear Medicine offered an initial appraisal of MIBG scanning in children with neuroblastoma and other solid tumors. The paper stated that "MIBG scans...may allow noninvasive monitoring of therapeutic response and completeness of surgical excision" (JNM, May 1986, Vol. 27:5, pp. 620-626).
Eight years later, Italian researchers used MIBG scans to monitor chemotherapy response in advanced neuroblastoma. They found success, declaring that "MIBG may allow lesion-by-lesion evaluation of the heterogeneity of neuroblastoma response to chemotherapy," giving it leverage over laboratory analysis, which offered more of a global picture of disease progress (JNM, September 1994, Vol. 35:9, pp. 1429-1435).
In the 21st century, nuclear medicine specialists are fine-tuning those early results. In 2001, an interdisciplinary group from the departments of radiology and pediatrics at the University of California, San Francisco (UCSF) tested neuroblastoma imaging with MIBG and a combined CT scanner-scintillation camera.
Their goal was to improve localization and uptake measurements of MIBG, which they achieved in three patients with tumor volumes ranging from 0.67 to 117 mL. The merging of serial CT images and SPECT resulted in a shorter scanning time and more defined anatomic volumes of interest (JNM, February 2001, Vol. 42:2, pp. 237-247).
The positive feedback for MIBG scans in these patients continues. In a presentation at the 2003 RSNA conference in Chicago, Dr. Soo-Ah Im from the Catholic University of Korea in Seoul shared her department’s experience with imaging neuroblastoma patients with 123I MIBG after chemotherapy. They then compared the modality to CT and MRI.
"It is difficult to differentiate viable neuroblastoma from scar tissue by means of CT and MR," Im said. "Uptake of MIBG indicates the presence of viable tumors."
Imaging and clinical data were gathered on 25 children with histologically proven neuroblastoma for this retrospective study. The data included primary, residual, and recurrent tumors as well as metastases. Serial imaging -- 90 MIBG scans, 122 CT scans, and 23 MR scans -- were reviewed.
At initial diagnosis, MIBG scans identified all suspected primary lesions that were histologically confirmed as neuroblastoma. Eleven patients with initially positive MIBG scans had normalized serial studies during the chemotherapeutic course. Of these 11, five experienced disease relapse, and the MIBG results were positive in all cases. In comparison, CT or MR showed relapse in three instances. In the fourth case, CT demonstrated a mass regression, while the MR results indicated a stable lesion in the fifth.
Fourteen of the 25 patients with initially positive MIBG scans showed persistent abnormalities over serial studies. In two cases, the CT scan demonstrated partial regression while MIBG uptake was persistent during therapy. In both of these cases, subsequent new lesions developed, Im reported.
Nine patients underwent surgery after chemotherapy; three of them continued to demonstrate increased MIBG uptake. Residual neuroblastoma was the culprit in these cases. There were six cases of ganglioneuroblastoma and ganglioneuroma, of which two showed normal MIBG results post-therapy. After a second surgery, transient increased MIBG uptake was seen anew in a previously normal adrenal region in the latter two cases.
Im concluded that MIBG scans were particularly adept at tracking the progression of new lesions. However, Im cautioned that MIBG scans did have some pitfalls, including an inability to rule out central nervous system lesions, which are better imaged with CT or MR. Nevertheless, her group now routinely performs MIBG scans, a minimum of three weeks after chemotherapy, in pediatric patents, she said.
The Korean group’s paper supports earlier research by French and U.S. physicians, who studied the early metastatic response by MIBG scans with the overall response and event-free survival (EFS) in neuroblastoma patients.
Their patient population consisted of 75 children with stage IV neuroblastoma who underwent MIBG scans after two and four cycles of induction therapy, as well as autologous stem-cell transplantation.
"The scans were read by two independent observers (concordance > 95%) using a semi-quantitative method. Absolute and relative (score divided by initial score) MIBG scores were then correlated with overall pre-transplantation response, bone marrow response, and EFS," wrote Dr. Katherine Matthay and colleagues from UCSF, the Institute Curie, and the Institute Gustave Roussy in Paris (Journal of Clinical Oncology, July 2003, Vol. 21:13, pp. 2486-2491).
According to the results, the pre-transplantation response rate was 81%, and the three-year EFS rate was 32%. The median relative MIBG score after two cycles of therapy was 0.5; after four cycles 0.24, and 0.12 after six cycles. The group concluded that patients with the above scores had improved EFS rates, making early assessment with semi-quantitative MIBG valuable for tailoring treatment and predicting response.
By Shalmali PalAuntMinnie.com staff writer
February 4, 2004
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Radioactive compound may aid in neuroblastoma treatment, December 6, 2000
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