Absorbed dose simulation of meta-211At-astato-benzylguanidine using pharmacokinetics of 131I-MIBG and a novel dose conversion method, RAP

Objective We aimed to estimate in vivo At-211-labeled meta-benzylguanidine (At-211-MABG) absorbed doses by the two dose conversion methods, using I-131-MIBG biodistribution data from a previously reported neuroblastoma xenograft model. In addition, we examined the effects of different cell lines and time limitations using data from two other works. Methods We used the framework of the Monte Carlo method to create 3200 virtual experimental data sets of activity concentrations (kBq/g) to get the statistical information. Time activity concentration curves were produced using the fitting method of a genetic algorithm. The basic method was that absorbed doses of At-211-MABG were calculated based on the medical internal radiation dose formalism with the conversion of the physical half-life time of I-131 to that of At-211. We have further improved the basic method; that is, a novel dose conversion method, RAP (Ratio of Pharmacokinetics), using percent injected dose/g. Results Virtual experiments showed that At-211-MABG and I-131-MIBG had similar properties of initial activity concentrations and biological components, but the basic method did not simulate the At-211-MABG dose. Simulated At-211-MABG doses from I-131-MIBG using the RAP method were in agreement with those from At-211-MABG, so that their boxes overlapped in the box plots. The RAP method showed applicability to the different cell lines, but it was difficult to predict long-term doses from short-term experimental data. Conclusions The present RAP dose conversion method could estimate At-211-MABG absorbed doses from the pharmacokinetics of I-131-MIBG with some limitations. The RAP method would be applicable to a large number of subjects for targeted nuclide therapy.