INTRAOPERATIVE LOCALIZATION OF NEUROBLASTOMA IN CHILDREN WITH I-123 OR I-125 RADIOLABELED METAIODOBENZYLGUANIDINE

Background. This study describes a novel method of intraoperative loca lization of neuroblastoma with a gamma-detecting probe, to detect in s itu tumor binding of radiolabeled I-123- or I-125-metaiodobenzylguanid ine (MIBG) and improve the quality of tumor resection. Methods. Fifty- eight children underwent 66 surgical procedures with intraoperative de tection of radiolabeled MIBG, All patients with positive MIBG scintisc ans at diagnosis were included in the study. A tumor/background ratio exceeding 2:1 at the time of operation was considered positive, indica ting a significant uptake of MIBG, compatible with the presence of mal ignant cells. The surgeons were requested to evaluate the contribution of the method to the surgical procedure. Sensitivity and specificity of the method with either I-123-labeled MIBG or I-125-labeled MIBG, on the basis of correlations between probe findings and pathologic analy sis of 288 resected specimens, were determined. Results. Intraoperativ e detection was helpful in 65% of surgical procedures, allowing a bett er definition of tumor limits and extension to locoregional nodes or d etection of small and nonpalpable tumors in sites with difficult surgi cal access, especially during operation for relapse. The detection was not contributory in 35% of the procedures (well-localized tumors, tho racic neuroblastoma for technical reasons, highly differentiated tumor s as ganglioneuroma, and tumors with mainly necrosis or fibrosis). The sensitivity of I-123 and I-125 was the same (91% and 92%), but the sp ecificity of I-125 (85%) was significantly higher than that of I-123 ( 55%) (p < 0.005). Conclusions. First, this study demonstrates the feas ibility of intraoperative detection, with radiolabeled MIBG, of neurob lastoma in children. We advocate the use of I-125 rather than I-123. S econd, the method is useful to improve the quality of macroscopic rese ction in widespread neuroblastoma with nodal involvement, in sites wit h difficult access, and in operations for relapse.