Purpose: To improve phantom-based dosimetry precision for nuclear medicine applications by providing a free dose calculation tool using advanced anatomy models.
Methods: Twelve National Cancer Institute adult/pediatric phantoms developed from patient images were used to calculate photon and electron Specific Absorbed Fractions (SAFs) for 68 source and 55 target regions, using MCNPX Monte Carlo code. S values were then derived from the SAFs for 299 radionuclides commonly used in nuclear medicine. The graphical user interface-based computer program, named National Cancer Institute dosimetry system for Nuclear Medicine (NCINM) was finally developed to facilitate data input/output. A comprehensive comparison of our S values was conducted with those previously published by Lamart et al. for iodine-131â€“ based on the ICRP reference adult computational phantoms, and OLINDA/EXM 1.0 â€“ based on the ORNL stylized phantoms.
Results: The ratios of our iodine-131 S values to those from Lamart et al. were on average 0.99Â±0.04Ïƒ and 0.98Â±0.03Ïƒ, respectively, for adult male/female phantoms in case of self-absorption within 8 major organs, and 0.79Â±0.46Ïƒ and 0.93Â±0.51Ïƒ, respectively, for adult male/female phantoms in case of cross-irradiation between these same organs. The ratios of our S values for iodine-131, technetium-99m and gallium-68 to those from OLINDA/EXM 1.0 were on average 0.91Â±0.15Ïƒ, 0.87Â±0.14Ïƒ, and 0.88Â±0.15Ïƒ over eight adult/pediatric phantoms, in case of self-absorption, and 1.34Â± 0.62Ïƒ, 1.48Â±0.82Ïƒ, and 1.36Â±0.62Ïƒ in case of cross-irradiation between the same organs, respectively.
Conclusion: A good agreement was observed between iodine-131 S values calculated on realistic phantoms: the NCI phantom series vs. the ICRP 110 reference phantoms. Greater differences were, however, revealed in S values between NCINM and OLINDA/EXM 1.0, especially for cross-irradiation, which emphasizes the impact of realistic human anatomy models on S values. The program will be useful for epidemiologic studies of risk and patient dose monitoring in nuclear medicine procedures.