ICRP-60

ICRP-60: 1990 Recommendations of the International Commission on Radiological protection

Khalil-Ur-Rahman AE,CNS, PNRA.

RP-003/1

April 15, 2008 Radiation Protection Course 2

Contents of ICRP-60

Introduction Basic Quantities in Radiological Protection Biological Aspects of Radiological

Protection Conceptual Framework of Radiological

Protection System of protection for proposed and

continuing practices System of protection in intervention


Introduction to ICRP

1928—International X-ray and radium protection committee by the decision of second International Conference of Radiology

1950– Restructured and Renamed 1959– ICRP Publication 1 1964- ICRP Publication 6 1966- ICRP Publication 9 1977- ICRP Publication 26 1980-1987– ICRP-26 was amended and

extended 1990– ICRP-60


ICRP-60 Quantities

Absorbed Dose Energy deposited per unit mass of tissue classical unit is the rad (radiation

absorbed dose) and the international unit is the gray (Gy). 1 Gy = 100 rads & Gy = Joule per kg

Equivalent Dose Does Absorbed dose clarify the nature, type and

energy of radiation ?

No, So absorbed dose weighted over a specific tissue multiplied by radiation weighting factor, WR is equivalent Dose.


ICRP-60 Quantities (contd.)

RTRRT DwH ,, .Not all radiation has the same biological effect, even for the same amount of absorbed dose. Equivalent dose is measured in an international (SI) unit called the Sievert (Sv) or an old unit rem.


ICRP Quantities

Effective Dose Probability of a harmful effect from radiation

exposure depends on tissue/part or parts of the body are exposed. Some organs are more sensitive to radiation than others. A tissue weighting factor is used to take this into account.

ET = ∑ WT . (∑ WR. DT,R) (Sv)

ET = ∑ WT . HT,R (Sv)


Dependence of WR

Relative Biological Effectiveness (RBE) “ The ratio of the amount of energy

from 200 KeV X-ray required to produce a given biological effect to the amount of energy from any other radiation to produce the same biological effect.”

RBE =______________________

Dose from test radiation, DT

Dose from reference radiation

For example, the RBE of 14 MeV neutron for killing American cockroach embryos is 16, since the lethal dose from the neutrons is only one-sixteenth that from x-ay.


Linear Energy Transfer (LET)

Ionizing Density of a radiation per unit distance or length traveled in tissue

Is a measure of the relative toxicity or damage-producing potential of a given absorbed dose for radiations.

The higher the rate of LET of the radiation, the greater would be the biological damage produced.

Variation of LET:Alpha, heavy nuclei and f.f > High Energy proton > neutrons > gamma and X-ray


Radiation and Tissue Weighting Factor

Type and Energy Range wR

Photons: all energies 1Electrons and muons: all energies 1Neutrons: energy < 10 keV 5Neutrons: 10 keV to 100 keV 10Neutrons: > 100 keV to 2 MeV 20

WT


Quality Factor and Weighting Factor

Radiation Q (Quality Factor) WR Radiation Weighting Factor

X, Gamma, beta 1 1

Neutron--Thermal 2 5

0.01 MeV 2.5 10

0.1 MeV 7.5 10

0.5 MeV 11 20

High Energy protons

10 5

Alpha, fission fragments, heavy nuclei

20 20


Occupational Dose LimitsOccupational Dose Limits for

Radiation Workers

Source of Radiation

Whole Body Dose is not to exceed 20mSv/ yr

Occupational Exposure Limit to the Extremities

The Dose Limit to theExtremities may not

exceed 500mSv / yr

Occupational Dose to the Lens of the Eye

Dose must not exceed 150mSv/ yr


Dose Limits per year

Body Part Occupational General Public

Effective Whole Body Dose

20 mSv per yearAvged over a period of

5 years1 mSv

Equivalent dose for Lens of the Eye

150 mSv 15 mSv

Equivalent dose for Skin 500 mSv 50 mSv

Equivalent dose for Hands and Feet

500 mSv

With the provision that effective whole body dose should not exceed 50 mSv in any one of five years


Biological Effects

Stochastic Effects Probability of a cancer/ cell damage

resulting from radiation usually increases with increments of dose, probably with no threshold, roughly proportional to dose, this effect is called stochastic effect.

Deterministic Effects Probability of causing cancer will be zero

at small doses, but above a certain level of dose (threshold) will increase steeply to unity (100%).


Deterministic Effects (cell killing) by curves

Unless dose is high, most types of cells are not killed immediately after the exposure

Studies of mammalian cells demonstrate that cell survival varies as a function of dose, which is described by survival curves and models……


Survival Curve and Model

For densely ionizing (High LET) radiations

S = e-D/DO

Where: S = survival D = dose

Do = dose at 37 % survival or reciprocal of slop

For sparsely ionizing (Low LET) S = 1- (1-e-D/D

O)n

‘n’ is the extrapolation number at zero dose.Do is the reciprocal slope of the exponential portion of

curve.


Survival Curve and Model

The initial region between 0 and 5 Gy (and often over a broader range), a linear quadratic equation on the average frequency (F) of lethal events:

F(D)= αD + βD2

the α and β are the linear coefficients, can range 1E-1 to 5E-1 Gy-1 and Quadratic coefficient 1E-1 and 5E-2 Gy-1


Survival Curves


Dose-Response

Acute radiation exposure can be sever in certain unforeseen/accident condition that death can result in individual members.

Death is generally is the result of sever cell depletion in one or more vital organ systems in the body, therefore dose-response becomes relevant.


Dose-Response Curves

Dose-Response model is used to predict the lethality in an exposed human populationNo individual is expected to die at low dosesSurvival-Dose relationship is often described by mid point LD50/60 ---dose at which 50% individual (exposed) will die with in 60 days (3-5 Gy from penetrating, Low LET, 1 MeV Gamma)


Risk Assessment models

Additive Risk (Projection) Model It postulates that the

excess mortality is broadly independent of natural mortality.

This model computes prob. Almost half of half prob. of multiplicative model

Multiplicative Risk (Projection) Model


Risk Models (contd.)

Multiplicative Risk Model: It is too simple, which is good for the exposure of adults. Japanese data show that neither this nor additive model adequately fits the pattern of mortality following the exposure of young children

Model does not imply multiplicative process rather it simply describes the prob. of cancer with time.


Attributable Death Probability

Attributable life prob. of death = area under the curve for dr/du

dp/du = ra. DWhere:dp/du =Age dependent

conditional death probability rate (radiation induced death probability rate) Assuming dose rate as a

function of age, dp/du can be calculated by dose-response relations


Comparison of Model Results

Additive model multiplicative ModelFor exposure at early age, prob. of is low at higher ages

For exposure at early age, prob. of is high at higher ages

Linear and simple and consider Biological Repair

No consideration of Biological Repair

For exposures at middle/adult (35) age, the differences are minor


Middle age Exposure

Attributable lifetime death prob. Rate, RR = ∫(dp/du)du {T,∞}

User

Minor differences for adult exposures


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