IMPLICATIONS OF THE UPTAKE OF I-131-RADIOLABELED METAIODOBENZYLGUANIDINE (METAIODOBENZYLGUANIDINE) FOR THE TARGETED RADIOTHERAPY OF NEUROBLASTOMA

Selective uptake of radiolabelled meta-iodobenzylguanidine (mIBG) in neuroblastoma provides a possible approach to biologically targeted radiotherapy of this disease. A mathematical model was used to predict absorbed doses to tumours of varying size from therapeutic I-131-mIBG, based on measurements of I-125-mIBG uptake in surgically excised tumours from six patients. Two size categories of tumour target were considered: bulk tumour and microscopic disease. The predicted absorbed doses were compared with doses calculated to achieve a 50% probability of tumour cure. The analysis shows that the probability of tumour cure depends strongly on mIBG uptake, effective half-life of mIBG in tumour and tumour diameter. Small microtumours may be relatively resistant to mIBG treatment owing to the limited absorption of I-131 beta-energy. The product of patient mass and percentage uptake per unit mass of tumour may be a useful indicator of therapeutic outcome when targeted radiotherapy is used for the treatment of paediatric tumours.