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PRINCE SATTAM BIN ABDUL AZIZ UNIVERSITYCOLLEGE OF PHARMACY

Nuclear PharmacyNuclear Pharmacy((PHT 433PHT 433 ) )

Dr. Shahid JamilDr. Shahid Jamil

The roentgen is the amount of x or γ radiation that produces

ionization of one electrostatic unit of either positive or negative

charge per cubic centimeter of air at 0C and 760 mmHg (STP).

Since 1 cm3 air weighs 0.001293 g at STP and a charge of

either sign carries 1.6 × 10-19 Coulomb (C) or 4.8 × 10-10

electrostatic units, it can be shown that

1R = 2.58 × 10-4 C/KgIt should be noted that the roentgen applies only to air and to x

or γ radiations. Due to practical limitations of the measuring

instruments, the R unit is applicable only to photons of less

than 3 MeV energy

1. The exposure dose1. The exposure dose (rontgen).(rontgen).

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b- Dose units b- Dose units

The unit of absorption dose.The absorbed dose of any ionizing radiation is the energy imparted to matter per unit mass of irradiated material.1 rad is that quantity of radiation which delivers 100 ergs per gm of matter.Absorbed dose (rads) = Exposure dose (Roentgens) X (C.F.)C.F. = Conversion factor depending on the density of the absorbing body and type of radiation.

2- The Radiation Absorbed Dose (RAD)2- The Radiation Absorbed Dose (RAD)

EnergyEnergyMevMevC.F. inC.F. inWaterWaterBoneBoneMuscleMuscle

Soft X raysSoft X rays0.050.050.8920.8920.3580.3580.9200.920Medium X raysMedium X rays0.50.50.9650.9650.9250.9250.9570.957γγ rays (from Corays (from Co6060))110.9650.9650.9190.9190.9570.957

The unit of absorption dose.The absorbed dose of any ionizing radiation is the energy imparted to matter per unit mass of irradiated material.1 rad is that quantity of radiation which delivers 100 ergs per gm of matter.Absorbed dose (rads) = Exposure dose (Roentgens) X (C.F.)C.F. = Conversion factor depending on the density of the absorbing body and type of radiation.

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The Rem is used to express human biological doses The Rem is used to express human biological doses as a result of exposure to one or several types of as a result of exposure to one or several types of ionizing radiations.ionizing radiations.Thus it is defined as: That dose of radiation which Thus it is defined as: That dose of radiation which produces in man the effects of 1 rad.produces in man the effects of 1 rad.

3. The Roentgen Equivalent Man (REM)3. The Roentgen Equivalent Man (REM)

Dose equivalent H (rems) = absorbed dose (rads) X (Q.F.) X (D.F.)Dose equivalent H (rems) = absorbed dose (rads) X (Q.F.) X (D.F.)

Q.F. = Quality Factor.Q.F. = Quality Factor.D.F. = Distribution factor depends on the energy D.F. = Distribution factor depends on the energy produced produced and angle of incidence.and angle of incidence.Both Q.F. and D.F. could be replaced by RBE Both Q.F. and D.F. could be replaced by RBE

(Relative Biological Effectiveness) = 1 for (Relative Biological Effectiveness) = 1 for γγ, X and , X and ββ

radiation and equal to 10 for radiation and equal to 10 for αα particles, protons and particles, protons and fast neutrons.fast neutrons.

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The primary event producing injury in a cell is the

production of ionization.

Excitation plays a small part, since radiations which

cause excitation without ionization, as UV, are less

effective in cell damage.

The dose of radiation which kills a cell may cause

ionization in only one molecule in 108.

THE BIOLOGICAL EFFECTS OF RADIATIONMechanism of Injury

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Direct radiation effects

Result from an ionization or

excitation within a biologically

functional molecule.

The occurrence of an ion cluster

within such a molecule releases

sufficient energy that terminate

biological function of the cell.

There are several theories concerning the mechanism

by which damage arises. but the damage results

from a mixture of direct and indirect effects.

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All nuclear disintegrations result directly or indirectly in production of fast-moving , charged particles. As these charged particles pass through matter they collide with atoms in their path and share their energies with the planetary electrons. Some of the latter may acquire sufficient energy to tear themselves away from the atom. Thus, a track of negative electrons and positively charged molecule together with its separated electron is called an ion pair and the "tearing-away" process is known as ionization.

1. Ionization

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Sometimes, when radiations react with matter,

ionization does not take place.

Instead, the atoms simply acquire extra energy from

the particles and assume an excited state, a process

known as excitation.

This excess energy may be discharged in several

ways, one which is the emission of light.

Alpha and beta particles cause ionization and

excitation directly.

2. Excitation

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Gamma radiation, because it is

without mass or charge, reacts

much less strongly with matter.

However, it does interact with

some of the planetary electrons

and these escape, often with high

energy, causing the above effects.

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Ionization and excitation of molecules in the body cause abnormal chemical reactions. For example, essential enzymes are inactivated, proteins are coagulated, nucleic acids in the genetic apparatus are damaged, and histamine- like substances are produced. These primary effects lead to the familiar signs of radiation damage.

Biological Effects:

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Indirect radiation Effects It result from the radiolysis of intracellular water (80 %) of most cells, and of any extracellular water which may be present. The principal effects are oxidativethat oxidations may result from reactions with the hydroxyl, hydroperoxy free radicals, hydrogen peroxide and the hydrogen radicals, which is responsible for destructive effects of radiation.As oxygen enhances radiation damage thus substances which protect against radiation are reducing agents (e.g. cysteamine, cysteine, glutathione).

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Reactions in the radiolysis of water (free radicals underlined)05/04/2305/04/23 1212L10,L11 and L12L10,L11 and L12

The free radicals •OH and •H may reacts

•OH + •OH H2O2

•H + •H H2

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Radiation Effects on the Human BodyThe effects of radiation on the entire organism depends on the proportion irradiated, Most severe with whole body exposure and least if only a small mass of insensitive tissue such as the hands is exposed.The degree of damage is influenced by the radiation intensity and the exposure time. In general, a number of small doses spread over several week does less damage than the same amount of radiation in one dose. However, this does not apply to the reproductive cells of the testes and ovaries, that the effect on which is cumulative.

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Short term effects.(prompt effect)Immediately appeared effect Whole body doses of about 25 rem would produce a transient change in the leucocyte count. Increasing the dose would result in increasing severity, 100 rem causing moderate illness (diarrhea, vomiting) in about 10 per cent of subjects, and severe illness in about1 per cent, the syndrome is known as radiation sickness. The median lethal dose (LD50) for death in 30 days is about 400 rem and with a dose of 600 rem there would be few survivors. Death from doses of this magnitude is usually the result of gut damage and a loss of resistance to disease. So that infections due to the intestinal microflors proceed.

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Some degree of protection against radiation sickness is afforded by the presence of reducing chemicals (cysteamine, glutathione) and by shielding certain important tissues such as the spleen and the bone marrow.

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Long term effects.

The results of long term exposure include permanent skin damage, bone necrosis and increased incidence of anemia, leukaemia, cataract and carcinomata. The human embryo is very sensitive and doses as small as 25 rem may lead to sever abnormalities.

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This was observed in early workers with X-rays who received very large doses over a prolonged period. A short exposure to intense radiation produces erythema. Longer exposure can cause brittleness and dryness (due to destruction of the sebaceous glands), loss of hair (due to damage to the hair follicle) and, if the dose is very large, burns. The latter heal very slowly and occasionally become malignant.

1- Skin Damage

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2. Somatic effectsThis may become evident from about two months to many years after exposure.They include cataract, severe anaemias, leukaemia, and cancer.Cancer tends to occur in tissues severely damaged by radiation. The latent period is very long and often exceeds twenty years.

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3. Genetic effectsRadiation has two effects on reproductive cells.

It can damage the chromosomes and increase the

frequency of gene mutation.

The former is not very important because it is

caused only by long exposure to low intensity X- and

gamma - rays.

Because damage to genetic material is cumulative

and irreversible, long exposure at low intensity

effects the mutation rate as much as an equivalent

dose of high intensity, i.e. there is no safe threshold

dose.

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The mutations will be hereditary by future

generations and most are harmful.

Consequently, it is not the exposed person who is at

special risk but, rather, future generations and,

through these, the whole population.

Thus it is important that radiation exposure should

be minimized during the early years.

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4- The effect on the rate of cell

divisionAll cells are susceptible to radiation damage depends

on the rate of cell division.

Thus tissues increase in resistance in the following

order: lymphocytes, erythrocytes, germinal

epithelium, intestinal epithelium, skin, internal

organs, brain, muscle, nerve.

This indicates that an important part of the damage

must be to the nuclear apparatus due to interference

with nucleic acid synthesis with the production of

abnormal chromosomes.

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Since any defect would result in imperfect

replication, that the effect of which would be

multiplied at each cell division, thus the greater the

rate of cell division the greater being the observed

damage. The effects in radiosensitive tissues (gonads, gut) commence at doses of about 10 rem and are severe at 100 rem. In liver and muscle, which are relatively radioresistant, doses greater than 1000 rem are needed to produce effects.

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Man is continually exposed to external and internal

radiations of natural origin (background radiation)

Exposure to RadiationRadiation from natural sources.

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(a) The earth's crust contains radioactive minerals

and therefore, man made structures of brick and

material expose to measurable amounts of

radiation.

(b) Cosmic (outer space) rays from outer space

(c) The atmosphere contains minute amounts of

radon and thorn, gaseous decay products of

radium and thorium.

(d) Radioactive constituents of the human body,

e.g.: 40K, 14C, and 226 Ra.

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The Gonads Dose Of Radiation From Natural Sources

SourcesSourcesDose Dose (mrads/wk)(mrads/wk)

Earth's crustEarth's crust

Cosmic radiationCosmic radiation

AtmosphereAtmosphere

Body constituentsBody constituents

i.e. the yearly dose is i.e. the yearly dose is

1-31-3

0.5 0.5

0.050.05

2-42-4

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Radiation from other sourcesMan also receives radiation from the accessories of

civilization.

Sources of such radiation include natural

background,

X-ray examination, Fall-out from test explosions

and industrial exposure.

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THE CONTROL OF RADIATION EXPOSURE

Maximum Permissible Doses

(MPD)One maximum permissible dose is that dose which,

received in a certain defined period and repeated

regularly and is not expected to cause appreciable

bodily harm.

Doses resulting from medical procedures are

excluded since they are regarded as necessary and

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The relationship governing the total permissible

cumulative

dose results

in an average dose rate of 5 rems per year for

persons engaged in radiation work from the age of 18

years.

It is assumed that there is no occupational exposure

to radiation permitted at age less 18 years.

Lower limits of permissible dose are set for the

general population, amounting to an addition equal to

the natural background dose, and for groups exposed

occasionally, such as laboratory maintenance workers.

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Organ of interestOrgan of interestMaximum Maximum permissiblpermissible dose e dose (rems) Per (rems) Per yearyear

External radiationExternal radiationGonads, blood-forming organs and the lens ofGonads, blood-forming organs and the lens ofthe eyethe eye

55

Weakly penetrating radiation:Weakly penetrating radiation:to the skin (except the hands, forearms, feetto the skin (except the hands, forearms, feetand ankles)and ankles)

3030

to the hands, forearms, feet and anklesto the hands, forearms, feet and ankles7575Internal radiationInternal radiationLimited exposure of internal organs resulting Limited exposure of internal organs resulting from from uptake (other than the thyroid, gonads and uptake (other than the thyroid, gonads and blood-blood-forming organs)forming organs)

1515

Whole body exposure resulting from Whole body exposure resulting from generalized uptakegeneralized uptake55

Maximum Permissible Dose For Radiation Workers

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This is an average dose rate.

The total permissible cumulative dose is given by:

Where N is the age in years, and not More than 60

rem may be accumulated by 30 age of years.

5)N- 18 (rems

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RadioprotectionDose rates at working positions

should always be measured.

The effect of distanceThe effect of distance

γγ-dose rates-dose ratesββ-dose rates-dose rates..

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The effect of distanceRadiations are emitted from a source in all directions so with a point source in a non-absorbing medium

where d is the distance from the source.

For γ-radiation air is almost a non-absorbing

medium. With β--particles there is considerable air absorption and external dose rates are not usually a problem.

dose rate α 1 /d2

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point source of that nuclide and have units of rongtens per millicurie hour at 1 cm. This is the most accurate basis for calculating the

dose at any distance from γ-emitting source

γ-dose rates The specific γ-ray constant (k-factor) is the dose rate

produced by the γ-radiation from a radionuclide at a distance of 1 cm from a 1 mCi

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β-dose rates.The whole body dose rates due to β--particles is not considered since the particles have a limited finite range and can be stopped completely by simple shielding. But some parts of the body, as the hands and forearms, may be exposed. For a point source of β—emitter, the exposure dose is given by :

where C is the source strength in curies.

Dose rate at 10 cm = 3100 C rads per hour in tissue

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The effect of β--energy is negligible.

It should be noted that β--particle doses to the hands

may be very large, and the handling of an unshielded

1 mCi source of 32P would give a dose to the hands of

about 3 rems per hour, assuming an average

distance of 10 cm.

This would result in the accumulation of one year's

maximum permissible dose in 25 h.

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From the inverse square law and the

appreciable air absorption of β--

particles, that doses may be reduced

by working at a sufficient distance

from a source with small amounts of

radioactivity.

With larger amounts of activity

shielding is necessary.

Shielding materials may consist of

lead, iron or concrete

Shielding

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Shielding against β--particles.

The maximum range of 2 MeV β--particles in air is

about

7.5 m.

But in denser materials the ranges are much less, the

range in Perspex is about 8.5 mm, thus 1 cm of

Perspex will give effective protection against β—

particles that a Perspex screen can be used as the

simplest method of shielding.

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Shielding against γ-particles.

The extent to which the intensity of a beam of γ-radiation is reduced by a barrier depends on the radiation energy and the atomic number and thickness of the barrier material. The tenth thickness of an absorber is that thickness required to reduce the intensity of radiation to one-tenth of its initial value.A greater thicknesses are required to reduce doses by the first factor of 10 than are needed for subsequent factors of 10.

e.g. for 60Co (mean γ- energy 1.25 MeV) the thickness of lead required to attenuate the dose by a factor of 1000 is approximately (4.4+3.6+3.6) cm = 11.6 cm.

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The calculation of the dose rates, which arise

due to the presence of radionuclides in the

tissues (internal radiation), is required only for

patients receiving diagnostic or therapeutic

doses of radionuclides or in the case of

accidental ingestion by radiation workers.

Estimation of Internal Dose Rates

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Factors influence such calculations

are:

(1)The rate of turnover of the element in the

body. The effective half life (Teff) is derived

from the actual half-life of the radionuclide

(T½) and the biological half- life (Tb), which

defines the turnover rate

Teff = T1/2 x Tb / (T1/2+Tb)

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(2) The degree of

absorption by the body

and of selective

localization within

particular organs and the

nature of the organ.(3) The energy and quality of the radiation, the

energy of α - and β- particles being absorbed

wholly within a small volume; whereas only a

part of the emitted γ-radiation is absorbed

within the body.

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RADIATION CONTROLSRADIATION CONTROLSA. Basic Control Methods for External RadiationA. Basic Control Methods for External Radiation

ALARA (As low as ALARA (As low as reasonable attainable) reasonable attainable) principlesprinciples Decrease Time

Increase Distance Increase Shielding

B. MonitoringB. Monitoring oPersonnel monitoringPersonnel monitoringoLaboratory monitoringLaboratory monitoring oBiological monitoringBiological monitoring

. .Basic Control Methods for External RadiationBasic Control Methods for External Radiation(ALARA)(ALARA)

TimeTime: Minimize time of exposure to minimize total : Minimize time of exposure to minimize total dose. Rotate employees to restrict individual dosedose. Rotate employees to restrict individual dose . .

DistanceDistance: Maximize distance to source to : Maximize distance to source to maximize attenuation in air. The effect of distance maximize attenuation in air. The effect of distance can be estimated from equationscan be estimated from equations..

ShieldingShielding: Minimize exposure by placing absorbing : Minimize exposure by placing absorbing shield between worker and sourceshield between worker and source . .

   

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