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 body weight 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.
Highlights
Rats at various ages were observed to present with different radiosensitivity and bioavailability for radiotracers commonly used in preclinical research
In typical preclinical positron emission tomography (PET)–computed tomography (CT) imaging studies, the animal is often exposed to nonnegligible radiation exposure, which may preclude the use of the animal in longitudinal studies, where it is used as its own control
The growth chart was obtained from 2-year study data on the Wistar Hannover GALAS rat[34] and used to calculate the length of rats at different age periods based on the weightlength formulas given by Donaldson[35]: Body length~143|logðBody weightz15Þ{134 ð1Þ
Summary
Rats at various ages were observed to present with different radiosensitivity and bioavailability for radiotracers commonly used in preclinical research. 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. For the adult rat older than 300 days, weight growth was reported to be due mostly to fat deposition.[33] Monte Carlo–based particle transport simulations of monoenergy photons/ electrons and spectra corresponding to decay schemes of positron-emitting radionuclides (C-11, N-13, O-15, F-18, Cu-64, Ga-68, Y-86, and I-124) were performed using MCNPX (Los Alamos National Laboratory, Los Alamos, NM) to calculate the absorbed fractions (AFs), specific absorbed fractions (SAFs), and S values for the considered series of models. Understanding the variability of the absorbed dose with body weight is important to appreciate the uncertainties involved in small-animal internal radiation dosimetry calculations
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