Age-Dependent Small-Animal Internal Radiation Dosimetry

Abstract

Rats at various ages were observed to present with different radiosensitivity and bioavailability for radiotracers commonly used in preclinical research. We evaluated the effect of age-induced changes in body weight on radiation dose calculations. A series of rat models at different age periods were constructed based on the realistic four-dimensional digital rat whole-body (ROBY) computational model. Particle transport was simulated using the MCNPX Monte Carlo code. Absorbed fractions (AFs) and specific absorbed fraction (SAFs) of monoenergetic photons/electrons and S values of eight positron-emitting radionuclides were calculated. The SAFs and S values for most source-target pairs were inversely correlated with body weight. Differences between F-18 S values for most source-target pairs were between −1.5% and −2%/10 g difference in bodyweight for different computational models. For specific radiotracers, the radiation dose to organs presents a negative correlation with rat body weight. The SAFs for monoenergetic photons/electrons and S values for common positron-emitting radionuclides can be exploited in the assessment of radiation dose delivered to rats at different ages and weights. The absorbed dose to organs is significantly higher in the low-weight young rat model than in the adult model, which would result in steep secondary effects and might be a noteworthy issue in laboratory animal internal dosimetry.