MABDOS: a generalized program for internal radionuclide dosimetry

Dosimetry calculations of monoclonal antibodies (MABs) are made difficult because the focus of radioactivity is targeted for a nonstandard volume in a nonstandard geometry, precluding straightforward application of the MIRD formalism. MABDOS, a program for performing internal radionuclide dosimetry, addresses this shortcoming. It accounts for the perturbations introduced by the inclusion of tumor(s) as additional source/target of radiation. Biodistribution data are conformed to a compartmental model, allowing the forward simulation of compartmental activity. Integration of the resultant time-activity curves yields cumulative activities for each compartment. Allowing compartments to represent physical organ spaces, cumulative activities are loaded into a column vector representing radionuclide source organs. A matrix multiplication between column vector and the appropriate S table is carried out. S factors for tumors as source and target organ are calculated by treating the tumor as a spherical perturbation to Standard Man geometry, and carrying out a Monte Carlo simulation on-the-fly. The software presents an integrated modeling/dosimetry environment and offers a viable methodology for performing prospective treatment planning.