Pediatric nuclear medicine dosimetry: A monte carlo study on S-value variability due to patient specific characteristics

Abstract

Introduction Personalized internal radiopharmaceutical dosimetry is of great interest in the pediatric population, in whom the risk from exposure to ionizing radiation is greatly debated. Our proposed methodology is being evaluated based on the ground truth of realistic Monte Carlo (MC) simulations and anthropomorphic models. Purpose Our goal is to compute S-values and quantify the absorbed dose in the majority of organs according to the specified radiopharmaceutical biodistribution and personalized anatomical characteristics. The S-value calculation procedure is validated against already published data, while the S-value variability in children of different anatomical characteristics is studied. Materials/Methods A validation study was carried out for the calculation of S-values using monoenergetic photon sources (10 keV–1 MeV). Furthermore, S-values were calculated using the biodistribution of 123 I-mIBG derived from clinical data of a 7 years old patient at 4 different time points. Male/female pediatric computational models were used for ages 5, 8 and 14 years respectively, in order to calculate S-values’ variability. The GATE MC toolkit was used for the calculation of organ absorbed doses. Results Calculated photon liver-to-kidneys S-values were compared to previously reported S-values. The differences were ∼2.6% for photons with energies 10 keV–100 keV, while a higher deviation ( 30%) was observed for 1 MeV photons. The comparison study for the three ages revealed several variations. S-values deviated ∼95% in liver, for girls with body masses ranging from 10.8 kg to 50.4 kg. Generally, children with similar body-masses had lower than ∼30% variations in specific organs. Conclusion Radiopharmaceutical dosimetry shows large variations due to the patients’ anatomies, thus personalized characteristics should be considered. Our study is ongoing, extending our investigation to additional pediatric phantoms and for a variety of radiopharmaceuticals. Disclosure n/a.