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MIRD Pamphlet No. 21: A Generalized Schema for Radiopharmaceutical Dosimetry—Standardization of Nomenclature

MIRD Pamphlet No. 21: A Generalized Schema for Radiopharmaceutical Dosimetry—Standardization of Nomenclature. 5/15/2009. MIRD. Medical Internal Radiation Dose Committee of the Society of Nuclear Medicine Original schema first issued in 1968

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MIRD Pamphlet No. 21: A Generalized Schema for Radiopharmaceutical Dosimetry—Standardization of Nomenclature

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  1. MIRD Pamphlet No. 21: A GeneralizedSchema for RadiopharmaceuticalDosimetry—Standardization of Nomenclature 5/15/2009

  2. MIRD • Medical Internal Radiation Dose • Committee of the Society of Nuclear Medicine • Original schema first issued in 1968 • Provides a framework for the assessment of absorbed dose to organs, tissue subregions, etc. from internally deposited radionuclides • Update to: • Standardize nomenclature • Adopts effective and equivalent dose • Highlights need to address deterministic effects

  3. Mean Absorbed Dose Rate • rT, rS: target tissue and source tissue • D(rT,t): dose rate at time t in target tissue rS S S rT rS

  4. Mean Absorbed Dose • Equation describes the dose to target tissue rT for integration time TD after administration of radionuclide • Time-dependent activity can be measured (e.g. w/ imaging, sampling) or modeled

  5. S(rT←rS,t) • Relates dose in target organ to activity in source organ • Function of emission spectrum, relative position of organs, shape, and size of organs • Tabulated for “standard” geometries and radionuclides

  6. S(rT←rS,t) • Ei = energy of ith nuclear transition • Yi = number of ith transition / nuclear transformation • Δi=EiYi • Фi = fraction of emitted energy absorbed in target • M(rT,t) is the mass of the target tissue

  7. Equivalent Dose • “The equivalent dose is a radiation protection quantity defined by the ICRP (7,8) and used to relate absorbed dose to the probability of stochastic health effects in a population exposed to radionuclides or radiation fields…” • Stochastic effects include cancer and heritable disease • Is not applicable to deterministic effects • Unit = Sievert (Sv)

  8. Equivalent Dose • H(rT,TD): equivalent dose • wR: Radiation weighting factor for radiation type R (1 for photons & electron, 20 for -particles)

  9. Effective Dose • “The effective dose E is a radiation protection quantity defined … for establishing annual limits of exposure to workers and members of the general public.” • Accounts for internal and external radiation sources • Unit = Sievert (Sv)

  10. Effective Dose

  11. Quantities Related to Deterministic Effects • RBE-weighted dose • BED • EUD • Isoeffective Dose

  12. RBE-weighted dose • RBE: Relative Biological Effectiveness • RBE is analogous to wR (from equivalent dose equation) • RBE depends on tissue and biologic endpoint

  13. BED • BED: Biologically Effective Dose • Usually used to compare different fractionation schemes • Accounts for dose rate variation in radionuclide therapy

  14. EUD • EUD: Equivalent Uniform Dose • Dose delivered to an organ is generally not uniform • EUD is the dose value that when uniformly delivered to an organ would yield the same response as the actual dose • Unit: Gray (Gy)

  15. Isoeffective Dose • Recently proposed to allow comparison of high LET and low LET radiation.

  16. Summary • MIRD schema is used to calculate dose from internal radionuclides • Stochastic effects • Equivalent dose: accounts for radiation type • Effective dose: accounts for radiation type and organs irradiated

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