Human pharmacokinetics and internal radiation dosimetry of normal organs after injection with the 99mTc-labeled monoclonal antibody (intact and fragments) are simulated by the WinAct program and IDAC (Internal Dose Assessment by Computer) software. The WinAct program is used to calculate the cumulative activity in organs and tissues. The calculated cumulative activity is inputted to the IDAC software, an internal dosimetry program for nuclear medicine based on the International Commission on Radiological Protection (ICRP) adult reference voxel phantom, and the absorbed doses by the organs and tissues are estimated. The obtained absorbed doses for the 99mTc-labeled monoclonal antibody (intact and fragments) are compared with the published figures by ICRP-128. The WinAct program method to calculate the cumulative activity is more accurate, as the fraction distribution, Fs, is described and calculated for organs, not only for intake, as in the ICRP model, but also for elimination.
Keywords: 99mTc; Absorbed dose; Cumulative activity; Internal exposure; Monoclonal antibodies.