Updates to Radionuclide Patient Release: I-131 Age-Specific Dose and Exposure Rate Coefficients

How does applying the latest radiation biokinetic and dosimetric models compare to traditional methods used by licensees for radionuclide therapy patient release – inclusive of age-specific patients and members of the public? Have a look at the latest publication by RED² Laboratory’s Landon Aziz, in the journal, Radiation Protection Dosimetry. Aziz is now putting his expertise to practice as a medical health physicist at Houston Methodist Hospital.

Updates to prior models established for adult I-131 to reflect age-specific biokinetic and dosimetric models for patient release calculations reflective of age-specific patients and members of the public.

Updated effective dose rate and exposure rate coefficients for age-specific receptors representing members of the public were computed for external exposures from age-specific patients administered I-131 to treat thyroid dysfunction for patient release evaluation. Coefficients were compared to the simplified point source method described by United States Nuclear Regulatory Commission Regulatory Guide (RG) 8.39, which does not consider age-specific parameters, morphometry or time-dependent 131I biodistribution. Monte Carlo age-specific phantom simulations were correlated with modified continuous voiding patient biokinetic models approximating age-specific dose and exposure rates as a function of time postadministration. Dose rates resulted in an overapproximation by a factor of ~3 from differentiated thyroid cancer patients (5% uptake) and by ~2 from hyperthyroid patients (80%) at 8 h postadministration compared to RG8.39. This study provides a paradigm where age-specific morphometry and biokinetic integration must be jointly considered when developing patient release guidelines for I-131 and future radionuclide therapies.

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