Author: Jae Won Jung, Daniel Lee 👨🔬
Affiliation: Thomas S. Wootton High School, East Carolina University Brody School of Medicine 🌍
Purpose: Monkeys have played a key role in enhancing our understanding of the behavior of radioactive materials within living organisms in the field of nuclear medicine. However, detailed dosimetric data, including S values for various source and target organs in the monkey anatomy and radionuclides, remains scarce. This study aims to create an extensive library of S values by employing a computational monkey model alongside Monte Carlo radiation transport techniques.
Methods: An S-value library for the monkey’s anatomical model was developed through the following steps. First, specific absorbed fractions (SAFs) were calculated for 35 source and 35 target organs using the MCNP6 Monte Carlo radiation transport code. Simulations were then conducted for both photons and electrons, spanning 27 monoenergetic energy bins ranging from 0.01 to 10 MeV. Finally, the S values for both photons and electrons were derived from the SAFs by incorporating energy spectrum data for 299 radionuclides, as outlined in ICRP Publication 107.
Results: The differences in self-absorption S values for larger organs were largely influenced by the type of radiation (positron/beta versus gamma). Crossfire S values showed trends consistent with those observed in SAFs, particularly concerning the distances between source and target organs. When comparing S values between the monkey model and ICRP reference human models, the monkey model more closely aligned with the self-absorption S values of a 1-year-old phantom, while the crossfire S values were more similar to those of a 10-year-old phantom.
Conclusion: This newly developed S value library will serve as a valuable tool for estimating organ doses in monkeys, especially when combined with radionuclide distribution data across their anatomical structures.