Experimental Evaluation of 65Zn Decorporation Kinetics Following Rapid and Delayed Zn-DTPA Interventions in Rats. Biphasic Compartmental and Square-Root Law Mathematical Modeling

The decorporation kinetics of internal radionuclide contamination is a long-term treatment raising modeling, planning, and managing problems, especially in the case of late intervention when the radiotoxic penetrated the deep compartments. The decorporation effectiveness of the highly radiotoxic 65ZnCl2 by Zn-DTPA (dosed at 3.32 mg and 5 mg/0.25 mL/100 g body weight) was investigated in Wistar male rats over a ten-day period under various treatments (i.e., as a single dose before contamination; as a single dose before and 24 h after contamination; and as daily administrations for five consecutive days starting on day 12 after contamination). The radioactivity was measured using the whole-body counting method. Mono- and bi-compartmental decorporation kinetics models proved applicable in the case of a rapid intervention. It was found that a diffusion model of the radionuclide from tissues to blood better describes the decorporation kinetics after more than ten days post treatment, and the process has been mathematically modeled as a diffusion from an infinite reservoir to a semi-finite medium. The mathematical solution led to a square-root law for describing the 65Zn decorporation. This law predicts a slower release than exponential or multiexponential equations, and could better explain the very long persistence of radionuclides in the living body. Splitting data and modeling in two steps allows a better understanding, description and prediction of the evolution of contamination, a separate approach to the treatment schemes of acute and chronic contamination.

Dosimetry of 131I for Occupational Radiation Workers by Whole Body Counting System

Internal radiation dosimetry of occupational radiation workers due to inhalation of 131I during maintenance at iodine 131I hot cell of Radioisotope Production Division (RIPD) of Bangladesh Atomic Energy Commission have been performed with Whole Body Counter (WBC) containing two large size NaI detector. The contaminated radioactivity of the radiation workers by 131I was immediately conducted using a WBC (CANBERRA, FASTSCAN model 2250) and counting was repeated again a few days later. The performance of whole body counter was checked by CANBERRA transfer phantom (model 2257) with a mixed source (20 ml vial). The intake was calculated by Apex-Invivo counting software and then corresponding dose in thyroid were estimated by using Integrated Modules for Bioassay Analysis (IMBA) Professional Plus code modules. The body activity due to intake of 131I and the total effective and equivalent dose in thyroid were also estimated and discussed.