Internal dosimetry: ICRP ymodels and data

Mats Isakssona s sa sso

Two systems for internal dosimetryTwo systems for internal dosimetry

Common scientific base

MIRD ICRP

Biologicalendpoints

Risk estimations

Time of intakeTime of intakeand intake can

be unknownand intake

usually known

Medical Internal Radiation Dose

ICRP-MIRDICRP-MIRD

• Calculation of absorbed dose is fundamentally similar in bothfundamentally similar in both systems

• Harmonization of concepts proposed in MURD Pamphlet No.proposed in MURD Pamphlet No. 21, 2009.

(The Journal of Nuclear Medicine 50(3) 2009 )(The Journal of Nuclear Medicine, 50(3), 2009.)

PathwaysPathways

IngestionInhalationInhalationInjection/Woundsj

Absorption (intact skin)

Difficulties in internal dosimetryDifficulties in internal dosimetry compared to external dosimetry

• You cannot measure internal dose

• Inhomogeneous distribution of the• Inhomogeneous distribution of the radionuclide within the body (and even within organs)within organs)

• Internal doses are protracted

• Different behaviour between elements

Models and calculationscalculations

Two types of dose estimationsTwo types of dose estimations

Dynamic modelling Direct measurementsDynamic modelling Direct measurements

Biokinetic orBiokinetic or Gamma cameraGamma cameraBiokinetic or pharmacokinetic

models

Biokinetic or pharmacokinetic

models

Gamma camera imaging: planar,

SPECT

Gamma camera imaging: planar,

SPECT

Calibration, retention fi i

Calibration, retention fi i

Known transfer and d l

Known transfer and d l curve fitting,…curve fitting,…model parametersmodel parameters

Input data from e g Calculations using theInput data from e.g. whole body counting

Calculations using the MIRD formalism

E IMBA E OLINDA EXME.g. IMBA E.g. OLINDA-EXM

Basic quantitiesBasic quantities

Equivalent dose (Sv)To organ or tissue T

R

RTRT DwH ,

– To organ or tissue T

– Radiation weighting factors from ICRP 60 (ICRP 103) stochastic effects(ICRP 103) – stochastic effects

Effective dose (Sv) TT HwEEffective dose (Sv)– Dose to the whole body that causes the

same detriment

T

TT

same detriment

– Tissue wighting factors from ICRP 60 (ICRP 103) stochastic effects(ICRP 103) – stochastic effects

Basic quantities - internalBasic quantities - internal

0tCommitted equivalent

dose (Sv)

tTT

o

dttHHdose (Sv)

– Integration time usually 50 y for adults & 70 y for children

to

70 y for children

Committed TT HwEeffective dose (Sv)

Calculated with dose coefficients e( )

T

TT

– Calculated with dose coefficients e() (Sv Bq-1) from e.g. ICRP 72

Dose coefficients (ICRP 72)Dose coefficients (ICRP 72)

What´s behind the doseWhat s behind the dose coefficients?

• Anatomy and physiology – reference man (ICRP 23)

• Source and target organs (ICRP 30)

• Absorbed fraction• Specific Absorbed Fraction SAF(TS)Specific Absorbed Fraction SAF(TS)

• Number of decays in source organ, in 50 yBi ki ti d l• Biokinetic models

Specific Effective Energy SEE(TS)Specific Effective Energy, SEE(TS)

YR: yield per disintegration (radiation R)

E : energyER: energy

wR: radiation weighting factor

AFR(TS): absorbed fraction

MT: mass of target tissue

RRRR STAFwEY

R T

RRRR

MSTAFwEYSTSEE

How to calculate the committedHow to calculate the committed effective dose

• Number of decays, Us

• Activity in source organ sActivity in source organ, s

• Biokinetic models

• Specific Effective Energy, SEE(TS)

• Committed• Committed equivalent dose

sST STSEEUH 50

• Committed effective dose

5050 T

TT HwE

How to determine U – ICRP 30-How to determine Us – ICRP 30-models

To some extent replaced by refined models, but still in use

• Lung model• Retention of inhaled activity – calculation of lung dose

• Transfer to blood through absorption

• Transfer to GI tract through mechanical transport of particlesparticles

• GI tract model• Retention of ingested activity dose to GI tract• Retention of ingested activity – dose to GI tract

• Fraction absorbed to blood (f1)

S stemic models metabolic element specific• Systemic models, metabolic – element specific

Lung model (ICRP 30)Lung model (ICRP 30)

• Was not designed to model biokinetic behaviour

• Conservative estimation of dosesdoses

• Calculates the number of decays in different regions

N-P: Nasal Passage; T-B: Tracheo-Bronchial region; P: Pulmonary region; Distribution determined by h i l l bilitchemical solubility

Lung model (ICRP 66) - regionsLung model (ICRP 66) - regions

• Can be applied for workers and the public for inhalation of particles, gases and vapours

• ”Reference worker” = a male breathing normallymale breathing normally through the nose while performing light workperforming light work

Lung model (ICRP 66) – particleLung model (ICRP 66) – particle deposition

• Regions divided into compartments

• Particle size• Particle size given by the AMADAMAD (Activity Median AerodynamicAerodynamic Diameter), often 5 moften 5 m

Lung model (ICRP 66) – particleLung model (ICRP 66) – particle transport

Lung model (ICRP 66) - absorptionLung model (ICRP 66) - absorption

• Compartment model for absorption to blood from all regions except ET1

• Three types of absorption: fast (F), moderate (M) and slow (S); determines the choice of parameter al esvalues

GI tract model (ICRP 30) - anatomyGI tract model (ICRP 30) - anatomy

GI tract model (ICRP 30) -GI tract model (ICRP 30) -compartments

Stomach

Small intestineSmall intestine

Upper large intestine

Lower largeLower large intestine

www.innerbody.com

GI tract model (ICRP 30) – absorptionGI tract model (ICRP 30) – absorption to blood

• Transfer to blood determined by f1(fraction of ingested activity that Bf

reaches the blood):

• Transfer parameters, (d-1), and mean SIB

f

1

p , ( ),residence time (h)

St SI (St) 24 d-1; 1 h( St) ;SI blood (B) 6f1/(1-f1)SI ULI (SI) 6 d-1; 4 hSI ULI (SI) 6 d ; 4 hULI LLI (ULI) 1,8 d-1; 13 hLLI outside (LLI) 1 d-1; 24 hLLI outside (LLI) 1 d ; 24 h

GI tract model (ICRP 100)GI tract model (ICRP 100)

Metabolic modelsMetabolic models

Describe the kinetics of a substance after it has entered thesubstance after it has entered the blood by

• absorption from lungs

b ti f GI t t• absorption from GI tract

• skin wounds or injection• skin, wounds or injection

Metabolic models (ICRP 30)Metabolic models (ICRP 30)

• Rather simple models (except alkaline earth metals)

• For calculating the number of decays in each organin each organ

• Not designed to model transfer rates lungs-blood or excretion rates

Metabolic models (ICRP 30)Metabolic models (ICRP 30)

• Organs modelled by one or more compartments

• First order kinetics

• No recycling back to blood (except for iodine)

• Radioactive progeny behave as their parents (except iodine and radonparents (except iodine and radon daughters)

Metabolic models (ICRP 30) –Metabolic models (ICRP 30) –Example: Cs

110/693.02/693.0 9.01.0 tt eetR

Metabolic models (ICRP 67) –Metabolic models (ICRP 67) –Example: Cs

HistoryHistoryDose coefficients ICRP 30Dose coefficients ICRP 30Revised dose limits and tissue weighting factors

Revised dosecoefficients, ALI (ICRP g g

(ICRP 60), (

61)Revised lung model and Revised dosegmetabolic models (ICRP 66, 67)

coefficients (ICRP 68)

Age dependent dosecoefficients for ingestion(ICRP 56 67 69) and

Summary, ICRP 72

(ICRP 56, 67, 69) and inhalation (ICRP 71)

Relevant publications 1Relevant publications 1

110 Ad lt R f C t ti l Ph t 2009110: Adult Reference Computational Phantoms 2009107: Nuclear Decay Data for Dosimetric Calculations

2008100: Human Alimentary Tract Model for Radiological

Protection 2006 89 Basic Anatomical and Ph siological Data for Use in89: Basic Anatomical and Physiological Data for Use in

Radiological Protection: Reference Values 2002 ICRP Supporting Guidance 3: Guide for the Practical

A li ti f th ICRP H R i t T tApplication of the ICRP Human Respiratory Tract Model 2002

72: Age-dependent Doses to the Members of the Public from Intake of Radionuclides Part 5, Compilation of Ingestion and Inhalation Coefficients 1996

Relevant publications 2Relevant publications 2

71 A d d t D t M b f th P bli f71: Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 4 Inhalation Dose Coefficients 1995

70: Basic Anatomical & Physiological Data for use in Radiological Protection: The Skeleton 1995

69: Age-dependent Doses to Members of the Public from g pIntake of Radionuclides: Part 3 Ingestion Dose Coefficients 1995

68: Dose Coefficients for Intakes of Radionuclides by68: Dose Coefficients for Intakes of Radionuclides by Workers 1994

67: Age-dependent Doses to Members of the Public from Intake of Radionuclides - Part 2 Ingestion DoseIntake of Radionuclides Part 2 Ingestion Dose Coefficients 1993

66: Human Respiratory Tract Model for Radiological Protection 1994Protection 1994

Relevant publications 3Relevant publications 3

56 A d d t D t M b f th P bli f56: Age-dependent Doses to Members of the Public from Intake of Radionuclides: Part 1 1989

48: The Metabolism of Plutonium and Related Elements 1986

30: Limits for Intakes of Radionuclides by Workers, Part 3 1981 (with supplement) ( pp )

30: Limits for Intakes of Radionuclides by Workers, Part 2 1980 (with supplement)

30 Li it f th I t k f R di lid b W k30: Limits for the Intake of Radionuclides by Workers, Part 1 1979 (with supplement)

23: Reference Man: Anatomical, Physiological and Metabolic Characteristics 1975

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