Age-dependent small-animal internal radiation dosimetry

Area of Science:

• Nuclear medicine
• Preclinical research
• Computational modeling

Background:

• Radiosensitivity and radiotracer bioavailability in rats vary with age.
• Age-induced changes in body weight can affect radiation dose calculations in preclinical studies.

Purpose of the Study:

• To evaluate the effect of age-induced body weight changes on radiation dose calculations in rats.
• To assess how body weight influences absorbed fractions (AFs), specific absorbed fractions (SAFs), and S values for common radiotracers.

Main Methods:

• Utilized realistic four-dimensional digital rat whole-body (ROBY) computational models for different age periods.
• Simulated particle transport using the MCNPX Monte Carlo code.
• Calculated AFs, SAFs for photons/electrons, and S values for eight positron-emitting radionuclides.

Main Results:

• Specific absorbed fractions (SAFs) and S values generally showed an inverse correlation with body weight.
• A 10 g difference in body weight corresponded to -1.5% to -2% difference in F-18 S values.
• Radiation dose to organs negatively correlated with rat body weight, with higher doses in younger, lighter rats.

Conclusions:

• SAFs and S values can be used to assess radiation doses in rats of different ages and weights.
• The higher absorbed dose in low-weight young rat models compared to adult models is a significant consideration for laboratory animal internal dosimetry.
• These findings highlight the importance of age and weight in accurate preclinical radiation dose assessment.