This study analyses the active marrow and endosteum dose differences between the new ICRP male and female reference computational phantoms and the stylized phantom for two thyroid agents. The active marrow and endosteum doses from 131I and 123I-Iodide were calculated for 0-55% maximum thyroid uptakes using the MCNP-4C Monte Carlo code. The biokinetic models were taken from ICRP Publication 53. To evaluate absorbed doses to red marrow and endosteum, the deposited energy was determined for the 19 spongiosa regions and 6 medullary cavities and was mass-weighted using the mass fractions available in ICRP Publication 116. The results were then compared with published values given in ICRP Publication 53. The poor anatomic realism of the stylized phantom used in ICRP Publication 53 leads to important dose differences between the ICRP voxel phantoms and the stylized phantom. The influence of the use of different bone material was also investigated. Underestimations of about 60% were observed for active marrow dose of the stylized phantom compared to reference voxel phantoms. The results highlight the importance of the accuracy of the shape and inter-organ distances of the anthropomorphic model used.

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