Activities of the International Commission on Radiological Protection

Transcription

1 Activities of the International Commission on Radiological Protection Wesley Bolch Advanced Laboratory for Radiation Dosimetry Studies (ALRADS) J. Crayton Pruitt Family Department of Biomedical Engineering University of Florida, Gainesville, FL Florida Chapter of the Health Physics Society Westin Hotel Lake Mary Lake Mary, Florida April 7, 2017

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5 ICRP Structure and Function

6 Recent ICRP Recommendations on Internal Dosimetry Recent and forthcoming ICRP publications Review of dose quantities in the ICRP system Methods and quantities needed for an internal dose coefficient A description of the improvements in the latest work

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8 ICRP Dose Quantities Absorbed dose, D The fundamental dose quantity given by where dε is the mean energy imparted to matter of mass dm by ionizing radiation. The SI unit for absorbed dose is joule per kilogram (J/kg) and its special name is gray (Gy). Equivalent dose, H T The dose in a tissue or organ T given by: where D T,R is the mean absorbed dose from radiation R in a tissue or organ T, and w R is the radiation weighting factor. Since w R is dimensionless, the unit for the equivalent dose is the same as for absorbed dose, J / kg, and its special name is sievert (Sv).

9 ICRP Dose Quantities Effective dose, E The tissue-weighted sum of the equivalent doses in all specified tissues and organs of the body, given by the expression: EE = TT ww TT HH TT ffffffffffff + HH TT mmmmmmmm 2 where H T is the equivalent dose in a tissue or organ, T, and w T is the tissue weighting factor. The unit for the effective dose is the same as for absorbed dose, J / kg, and its special name is sievert (Sv).

10 ICRP 103 Radiation Weighting Factors

11 ICRP 103 Tissue Weighting Factors

12 ICRP Dose Coefficients Internal Exposures Dose coefficient Internal Exposures For adult workers, a dose coefficient is defined as either the committed equivalent dose in organ or tissue T per activity intake, h T (50), or the committed effective dose per intake, e(50), where 50 is the dose-commitment period in years over which the dose is calculated. Note that elsewhere the term dose per intake coefficient is sometimes used. Intake and Systemic Biokinetic Models Radionuclide Decay Scheme Anatomic Phantom and Radiation Transport Simulation

13 Biokinetic Models for Radionuclide Transport When calculating internal dose coefficients it is necessary to have knowledge of the location of activity as a function of time. Radionuclide location and movement through the body is modeled with first order kinetics to and from biological compartments. Important to remember that the compartments are mathematical containers for material in constituent tissues. Results in a system of solvable, coupled differential equations.

14 ICRP 66 Human Respiratory Tract Model ICRP 100 Human Alimentary Tract Model ICRP 130 Systemic Biokinetic Models

15 Biokinetic Models - Publication 30 For 137 Cs, Publication 30 assumes total body uniform distribution modeled as two compartments: ff 1 = 0.10 aaaaaa ff 2 = 0.9 λλ eeeeee1 = λλ bb1 + λλ RR = llll2 2 dd + llll2 30 yy λλ eeeeee2 = λλ bb2 + λλ RR = llll2 110 dd + llll2 30 yy yy 365 dd yy 365 dd

16 Biokinetic Models Current Generation Transfer coefficients (d -1 ) for systemic cobalt Compartments Transfer Coefficient (d -1 ) Blood 1 to Liver 1 70 Blood 1 to Urinary bladder contents 60 Blood 1 to Right colon contents 4.0 Blood 1 to ST0 18 Blood 1 to ST1 10 Blood 1 to ST2 4.0 Blood 1 to Cortical bone surf 6.0 Blood 1 to Trabecular bone surf 6.0 Blood 1 to Kidneys Blood 1 to Kidneys Blood 1 to Blood 2 12 Blood 2 to Blood Liver 1 to SI cont Liver 1 to Blood Liver 1 to Liver Liver 2 to Blood ST0 to Blood ST1 to Blood ST2 to Blood Cortical bone surf to Blood Cortical bone surf to Cortical bone vol Trabecular bone surf to Blood Trabecular bone surf to Trabecular bone vol Cortical bone vol to Blood Trabecular bone vol to Blood Kidneys 1 to Urinary bladder contents Kidneys 2 to Blood surf = surface, vol = volume, SI = small intestine

17 Biokinetic Models - Numerical Solution ddaa ii,jj (tt dddd MM = AA ii,kk λλ ii,kk,jj AA ii,jj kk=1 kk jj MM kk=1 kk jj λλ ii,jj,kk + λλ ii PP ii 1 PP + AA kk,jj ββ kk,ii λλ ii kk=1 M is the number of compartments describing the kinetics; λλ ii,jj,kk is the fractional transfer rate of chain member i from compartment j (donor compartment) to compartment k (receiving compartment) in the biokinetic model; PP λλ ii is the physical decay constant of chain member i; and ββ kk,ii is the fraction of the decays of chain member k forming member i.

18 Decay Chains Independent Systemic Biokinetics Parent Progeny λ 4 Kidney_1 Blood λ 3 λ 1 λ 2 Other_1 Blood λ 5 λ 6 λ 8 λ 7 Other_2 An Other compartment contains a set of defined tissues which, if not explicitly modeled, are accounted for in the Other compartment(s). ICRP 71 describes two approaches for handling treatment of the Other compartments in members of a decay chain.

19 More on Decay Chain Biokinetics Physical decay in the parent s Other_1 compartment requires an Other_1 compartment to be created in the Progeny systemic model. The tissues comprising Other_1 are the same in both the Parent and Progeny model. (In this case, those tissues include Kidney.) The amount of progeny in the kidney is then the sum of the amount in the Kidney_1 compartment and a mass fraction of the amount in Other_1. Blood Parent λ 3 λ 1 λ 2 λ p Other_1 λ p Progeny Blood λ 4 λ 5 λ 6 λ 8 λ 7 λ 7 Kidney_1 Other_2 Other_1

20 ICRP Nuclear Decay Data

21 Reference Person and the Reference Phantoms

22 Dose Calculations with the ICRP System HH TT = AA SS SS ww rr TT rr SS rr SS The radiation-weighted S coefficient [Sv (Bq-s) -1 ] for a radionuclide is calculated as: SS ww rr TT rr SS = ww RR EE RR,ii YY RR,ii Φ rr TT rr SS, EE RR,ii RR ii EE RR,ii is the energy of the i th radiation of type R emitted in nuclear transformations of the radionuclide; YY RR,ii is the yield of the i th radiation of type R per nuclear transformation, [(Bq s) -1 ]; ww RR is the radiation weighting factor for radiation type R; and Φ rr TT rr SS, EE RR,ii is the SAF, defined as the fraction of energy EE RR,ii of radiation type R emitted within the source tissue r S that is absorbed per mass in the target tissue r T (kg -1 ).

23 Adult Specific Absorbed Fractions - Previous ICRP Publication 30 Appendix I of ICRP Publication 23 MIRD Phantom Subsequent ICRP Publications Specific Absorbed Fractions of Energy at Various Ages from Internal Photon Sources (ORNL TM-8381)

24 Adult Specific Absorbed Fractions - Current Publication 110 Reference Phantoms

25 Dosimetry Specific Absorbed Fractions

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30 Forthcoming Reports Occupational Intakes of Radionuclides (OIR) OIR Part 1 general framework (update to ICRP 130) OIR Part 2 H, C, P, S, Ca, Fe, Co, Zn, Sr, Y, Zr, Nb, Mo, and Tc OIR Part 3 Ru, Sb, Te, I, Cs, Ba, Ir, Pb, Bi, Po, Rn, Ra, Th, and U OIR Part 4 lanthanides and remaining actinides OIR Part 5 everything else

31 Pediatric Specific Absorbed Fractions Φ(Liver Liver) Φ(Muscle Liver) ICRP Series of Pediatric Reference Phantoms Derived from UF/NCI hybrid phantom series Photon and Electron SAFs currently being completed QA to start within ICRP TG 96 Support U.S. Environmental Protection Agency 31

32 Pregnant Female Specific Absorbed Fractions Models at 8 week to 38 weeks post-conception ICRP Series of Fetal and Pregnant Female Phantoms Derived from UF hybrid phantom series developed for the SOLO Project Primary photon and electron SAFs beginning currently QA to be completed under TG 96 Support U.S. Environmental Protection Agency 32

33 Summary - Improvements in the Updated Dosimetry First-time use of fractional values of electron absorbed fractions Discernment of wall sources for the Publication 100 alimentary tract organs Integration of phantom-derived SAFs with those derived from stylized models of the alimentary tract and respiratory tract Interpretation of ICRP Publication 89 Reference Masses inclusive or exclusive of blood content? Computation of blood sources example of a distributed organ Treatment of progeny in-growth with unique systemic biokinetics First-time consideration of coefficients giving effective dose per bioassay content

34 ICRP Dose Coefficients External Exposures Dose Coefficient External Exposures A coefficient relating a dose quantity to a physical quantity. For external exposure, the physical quantity fluence or air kerma is chosen. Idealized occupational radiation fields Idealized environments of radionuclide contaminated air, water, or soils 34

35 ICRP Dose Coefficients - External Publication 74 (1996) Based upon review of published dose coefficients Mixture of stylized and voxel phantoms Publication 116 (2010) Based upon new MC calculations using the Publication 110 phantom Extensive benchmarking of various MC transport codes 35

36 ICRP Task Group 90 Age-Dependent Dose Coefficients for Env. Exposures 36

37 Potential Future Efforts It is emphasized that Reference Dose Coefficients are to be applied under the ICRP System of Radiological Protection. However, the research methods used by the ICRP in establishing reference dose coefficients may be expanded to provide tools for individualized dose reconstruction following accidental occupational or environmental releases. For example, an expanded library of phantoms modeling variations in subject height, weight, and thus body morphometry can be applied to more personalize the dose assessment. 37

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