RADAR reference adult, pediatric, and pregnant female phantom series for internal and external dosimetry.

UNLABELLED: A new generation of reference computational phantoms, based on image-based models tied to the reference masses defined by the International Commission on Radiological Protection (ICRP) for dose calculations, is presented. METHODS: Anatomic models based on nonuniform rational b-spline modeling techniques were used to define reference male and female adults, 15-y-olds, 10-y-olds, 5-y-olds, 1-y-olds, newborns, and pregnant women at 3 stages of gestation, using the defined reference organ masses in ICRP publication 89. Absorbed fractions and specific absorbed fractions for internal emitters were derived using standard Monte Carlo radiation transport simulation codes. RESULTS: Differences were notable between many pairs of organs in specific absorbed fractions because of the improved realism of the models, with adjacent organs usually closer and sometimes touching. Final estimates of absorbed dose for radiopharmaceuticals, for example, were only slightly different overall, as many of the differences were small and most pronounced at low radiation energies. Some new important organs were defined (salivary glands, prostate, eyes, and esophagus), and the identity of a few gastrointestinal tract organs changed. CONCLUSION: A new generation of reference models for standardized internal and external dose calculations has been defined. The models will be implemented in standardized software for internal dose calculations and be used to produce new standardized dose estimates for radiopharmaceuticals and other applications.

Voxel-based mouse and rat models for internal dose calculations.

UNLABELLED: The ability to estimate absorbed doses in experimental animals to which radiolabeled material has been administered may be important in explaining and controlling potential radiation toxicity observed during preclinical trials. Most previously reported models for establishing doses to small animals have been stylized and mathematically based. This study establishes dose factors for internal sources in realistic models of a typical mouse and a typical rat, based on image data obtained using a dedicated small-animal CT scanner. METHODS: A transgenic mouse (body mass, 27 g) and a Sprague-Dawley rat (body mass, 248 g) were imaged using the dedicated small-animal CT scanner. Identified organs were segmented using computer tools that Vanderbilt University applies to process human images for 3-dimensional dosimetry. Monte Carlo N-particle transport code (MCNP) input files were prepared from the 3-dimensional, voxel-based image data. Using methods established for human studies, radiation transport calculations of absorbed fractions (AFs) were performed using MCNP, version 4C, on the segmented images, and dose conversion factors for several radionuclides were developed. RESULTS: AFs were established at discrete energies for electron and photon sources assumed to be uniformly distributed throughout approximately 10 source and target regions in both models. Electron self-irradiation AFs were significantly less than 1.0 for many organs, at energies above 0.5 MeV, and significant cross irradiation was observed for high-energy electrons, such as those from (90)Y or (188)Re, in many organs. Calculated dose conversion factors reflected these trends and agreed well with the results of other authors who have undertaken similar investigations. CONCLUSION: The AFs calculated in this study will be useful in determining the dose to organs for mice and rats similar in size to those studied here. The segmented, voxel-based models developed here can be used for external dose calculations as well.