Ionizing radiation...Effects

and Safety

Dr/Ahmed bahnassy

Consultant radiologist

PSMMC

what every physician must know

Aims of lecture• To become familiar

with the mechanisms & biological effects following exposure to ionizing radiation.

• To be aware of the risks of ionizing radiation .

• To know main safety issues of protection.

RADIATION:- Radiation is the energy that comes from a source and travels through some material or space as waves or photons.

IONIZING RATIATION:-This kind of radiation on interaction with matter produce charged particles called ions. This type of radiation has enough energy to break chemical bonds. NON-IONIZING RATIATION:-Radiation that does not have enough energy to break chemical bonds but can vibrate atom. It cannot produce ions.

SOURCES OF RADIATION

UNITS OF RADIATION:-

1) Roentgen (R):- Radiaton exposure in a volume of air.

2) Rad:-It is the unit of absorbed dose.The SI unit of absorbed dose is Gray (Gy)1 Gy=100 rad

3) Rem:-

It is the unit of effective dose.Used only in radiation protection.The SI unit is Sievert1 Sv= 100 rem 1 mSv = 0.001 Sv.

0.01 mSv0.5 Chest X-ray.

0.02mSv1 CXR

0.07 mSv 3.5 CXR

1.3mSv65 CXR

0.7mSv 1.0mSv 2.5mSv 3.0mSv 7.0mSv 35 CXR 50 CXR 125CXR 150CXR 350CXR

2.3mSv 8.0mSv 10mSv

115 Chest 400 CXR 500 CXR X-rays.

15 mSv 750 CXR

4 mSv200 CXR

6 mSv 300 CXR

THYROID SCAN RENAL SCAN LUNG PERFUSION 1.0 mSv 1.0 mSv 1.0 mSv 50 CXR 50 CXR 50 CXR

BONE SCAN PET HEAD (FDG) CARDIAC GATED 4.0 mSv 5.0 mSv 6.0 mSv 200 CXR 250 CXR 300 CXR

Ionizing Ionizing Radiation..How Radiation..How effects are producedeffects are produced

Ionizing Radiation is Ionizing Radiation is the the removal of an removal of an electronelectron

from an atom leaving from an atom leaving an an unstable molecule unstable molecule which may then which may then break apart to form break apart to form free radicals.free radicals.

http://www.paradigmlink.com/ionrad.shtml

The weapon

Linear Energy Transfer (LET)Linear Energy Transfer (LET)

The average energy deposited per unit The average energy deposited per unit

length of track.length of track.

Measured in kiloelectron volts per Measured in kiloelectron volts per micronmicron

(10(10-6-6 m) m)

Low LET / High LETLow LET / High LET

Low LETLow LETLow mass, increased Low mass, increased

travel distance (gamma rays, travel distance (gamma rays, x-rays).x-rays).

Sparsely ionizing with Sparsely ionizing with

random interactions. random interactions.

Causes damage primarily Causes damage primarily

through indirect action or through indirect action or

may cause single strand may cause single strand

breaks (which are repairable). breaks (which are repairable).

http://staff.jccc.net/PDECELL/biochemistry/dna.gif

e-

Low LET / High LETLow LET / High LET

High LETHigh LET– Large mass, decreased Large mass, decreased

travel distance (alpha travel distance (alpha particles, protons, low particles, protons, low energy neutrons).energy neutrons).

– Causes dense Causes dense ionization ionization

along its path with a along its path with a high probability of high probability of interacting directly with interacting directly with DNA.DNA.

http://staff.jccc.net/PDECELL/biochemistry/dna.gif

α++

Ionizing RadiationIonizing Radiation

The reactions caused by ionizing The reactions caused by ionizing radiation occur rapidly, they are radiation occur rapidly, they are nonselective and nonselective and

random.random.The majority of damage caused by The majority of damage caused by

radiation is due to chemical radiation is due to chemical reactions with water within the cell.reactions with water within the cell.

The injury mechanism

H2O HOH+

H+

OH*

H* OH-

e- + H2O HOH-

water

negatively charged water

molecule

Hydrogen ion

Hydroxyl radical

electron water

Positively charged water

molecule

hydrogen radical

Hydroxyl ion

The negatively charged water molecule dissociates into a hydrogen radical and a hydroxyl ion.

ReactionsReactions

The previous reactions produce free The previous reactions produce free

electrons (eelectrons (e--), the ions H), the ions H-- and OH and OH--, ,

the free radicals H* and OH*.the free radicals H* and OH*.The fate of these products are…….The fate of these products are…….

Free RadicalsFree Radicals

A free radical is an atom or A free radical is an atom or molecule that has an molecule that has an unpaired unpaired

electron in its valence shell.electron in its valence shell. These free radicals are These free radicals are

non-selective when pairing non-selective when pairing up up

with electrons from otherwith electrons from other

atoms, including those that atoms, including those that

make up the DNA molecule.make up the DNA molecule.

Direct Action / Indirect Direct Action / Indirect ActionActionDirect ActionDirect Action

Causes damage directly to DNA or other Causes damage directly to DNA or other important important

molecules in the cell.molecules in the cell.More likely when the beam of charged particles More likely when the beam of charged particles consist of alpha particles, protons, or electrons consist of alpha particles, protons, or electrons

Indirect ActionIndirect ActionCauses damage by interacting with the cellular Causes damage by interacting with the cellular medium producing free radicals which then medium producing free radicals which then

damage the DNA molecule.damage the DNA molecule.More likely when x-rays or gamma-rays compose More likely when x-rays or gamma-rays compose

the beam.the beam.

Direct Action / Indirect Direct Action / Indirect ActionAction

DNA DamageDNA Damage

The arrangement of The arrangement of nitrogenous bases nitrogenous bases provide a blueprint for DNA for the provide a blueprint for DNA for the synthesis of specific proteins necessary synthesis of specific proteins necessary for individual cell function.for individual cell function.

In the event of a In the event of a loss or change loss or change of one of one or more of the nitrogenous or more of the nitrogenous bases....base sequence and bases....base sequence and normal functioning of the cell is altered.normal functioning of the cell is altered.

Another form of DNA damage due to Another form of DNA damage due to radiation involves a radiation involves a breakbreak in the in the hydrogen bonds between the Adenine hydrogen bonds between the Adenine – Thymine and Cytosine – Guanine – Thymine and Cytosine – Guanine base pairs. These bonds function to base pairs. These bonds function to keep the DNA strands togetherkeep the DNA strands together

Bonds can also break between Bonds can also break between deoxyribose sugar and the phosphate deoxyribose sugar and the phosphate groups which can lead togroups which can lead to cross-linking cross-linking of DNAof DNA

The target

Chromosome AberrationsChromosome Aberrations If the chromosome fragments are If the chromosome fragments are

near one another they have a high near one another they have a high chance of reattaching in their chance of reattaching in their original position – causing no future original position – causing no future damage to the cell.A process damage to the cell.A process known as known as restitution.restitution.

In In translocationstranslocations and inversions, no and inversions, no genetic information is lost, but the genetic information is lost, but the rearrangement of gene sequence rearrangement of gene sequence will alter protein synthesis.will alter protein synthesis.

In a In a deletiondeletion, a chromosome , a chromosome fragment is not replicated during fragment is not replicated during the next mitosis, the genetic the next mitosis, the genetic information is lost. The effects this information is lost. The effects this has on the cell depends on the has on the cell depends on the amount and type of information amount and type of information lost.lost.

Translocation

Inversion

Deletion

The effects

Chromosome deletion

Chromosome translocation

IAEA 3 : Biological effects of ionizing radiation

Outcomes after cell exposure

DAMAGEREPAIRED

CELL DEATH(APOPTOSIS)

TRANSFORMED CELL

DAMAGE TO DNA

DNA Mutation

Cell survives but mutated

Cancer ?

Cell death

Mutation repaired

Unviable Cell

Viable Cell

IAEA 3 : Biological effects of ionizing radiation

Repair of DNA damage

• RADIOBIOLOGISTS ASSUME THAT THE REPAIR SYSTEM IS NOT 100% EFFECTIVE.

Cancer initiationCancer initiation

NORMAL TISSUE

CELL INITIATION

An initiating event

creates a mutation in

one of the basal cells

DYSPLASIA

More mutations occurred.

The initiated cell has

gained proliferative

advantages.

Rapidly dividing cells

begin to accumulate

within the epithelium.

BENIGN TUMOR

More changes within

the proliferative cell line lead

to full tumor development.

MALIGNANT TUMOR

The tumor breaks trough

the basal lamina.

The cells are irregularly

shaped and the cell line is

immortal. They have an increased

mobility and invasiveness.

METASTASIS

Cancer cells break through

the wall of a lymphatic

vessel or blood capillary.

They can now migrate

throughout the body and

potentially seed new tumors.

A simple generalized scheme for multistage oncogenesis

Damage to chromosomal DNAof a normal target cell

Failure to correctDNA repair

Appearance of specificneoplasia-initiating mutation

Promotional growthof pre-neoplasm

Conversion to overtlymalignant phenotype

Malignant progression and tumour spread

RadiosensitivityRadiosensitivity

Actively reproducing Actively reproducing cells are more cells are more radiosensitive than mature cells.radiosensitive than mature cells.

During During mitosismitosis, the cell is in a , the cell is in a stressed stressed state and shows an increase in damage state and shows an increase in damage caused by radiation.caused by radiation.Cells that have Cells that have decreased decreased levels of levels of differentiation are more radiosensitive differentiation are more radiosensitive than specialized cells.than specialized cells.

The Cell Cycle

An ordered set of events, culminating in cell growth and division into two daughter cells

Tc, full mitotic cycle

G2

(2nd gap)

M(mitosis)

S(DNA Synthesis phase)

G1

(1st gap)

Cells that cease division

Radiosensitivity & Mitotic Cycle Cell cycle components

M, G1, S, G2

Cell cycles times vary largely due to G1 crypt cells, 9 - 10 hours stem cells (mouse skin) 200 hr

Sensitivity Cells most sensitive close to mitosis Resistance greatest in latter part of S For long G1’s, there is an early resistance period followed by

sensitive one at the end of G1 G2 ~ M in sensitivity

IAEA 3 : Biological effects of ionizing radiation

Radiosensitivity

Muscle

Bones

Nervous system

Skin

Mesoderm organs (liver, heart, lungs…)

Bone Marrow

Spleen

Thymus

Lymphatic nodes

Gonads

Eye lensLymphocytes (exception to the RS laws)

Low RSMedium RSHigh RS

Fractionation in Fractionation in radiotherapyradiotherapy Instead of a single treatment Instead of a single treatment consisting of a high dose, consisting of a high dose,

fractionation divides the dose fractionation divides the dose to be delivered over a period to be delivered over a period of time, usually 6-8 weeks.of time, usually 6-8 weeks.

At low doses of radiation, At low doses of radiation, normal cells normal cells have an increased have an increased

survival rate because of their survival rate because of their ability to repair sublethal ability to repair sublethal damage before the next damage before the next fraction of radiation is fraction of radiation is delivered.delivered.

Tumor cells Tumor cells do not possess do not possess the repair enzymes the repair enzymes necessary to necessary to

keep up with the repairs and keep up with the repairs and as a result the cell is as a result the cell is overwhelmed and is overwhelmed and is

destroyed.destroyed. http://www.usoncology.com/CompanyInfo/PhotoLibrary.asp

Two effects of radiation exposure: deterministic (threshold) stochastic: cancer

Radiation Standards set below threshold set to limit stochastic risk

Dose-Response Relationships

Non-Stochastic (Deterministic) Effects Occurs above threshold

dose Severity increases with

dose Alopecia (hair loss) Cataracts Erythema (skin reddening) Radiation Sickness Temporary Sterility

Stochastic (Probabilistic) Effects

Occurs by chance Probability increases with dose

Carcinogenesis Mutagenesis Teratogenesis

IAEA 3 : Biological effects of ionizing radiation

Radiation health effects

DETERMINISTICSomaticClinically attributable in the exposed individual

CELL DEATH

STOCHASTICsomatic & hereditaryepidemiologically attributable in large populations

ANTENATALsomatic and hereditary expressed in the foetus, in the live born or descendants

BOTH

TYPEOF

EFFECTS

CELL TRANSFORMATION

Radiation effects and Syndromes

IAEA 3 : Biological effects of ionizing radiation

Injury

Threshold

Dose to

Skin (Sv)

Weeks to

Onset

Early transient erythema 2 <<1Temporary epilation 3 3

Main erythema 6 1.5Permanent epilation 7 3Dry desquamation 10 4Invasive fibrosis 10Dermal atrophy 11 >14Telangiectasis 12 >52

Moist desquamation 15 4Late erythema 15 6-10

Dermal necrosis 18 >10Secondary ulceration 20 >6

Skin damagefrom prolongedfluoroscopicexposure

Skin reactions

IAEA 3 : Biological effects of ionizing radiation

Skin injuries

IAEA 3 : Biological effects of ionizing radiation

Effects in eye

• Eye lens is highly RS.

• Coagulation of proteins occur with doses greater than 2 Gy.

• There are 2 basic effects:

From “Atlas de Histologia...”. J. Boya

Histologic view of eye:

Eye lens is highly RS, moreover, it is surrounded by highly RS cuboid cells. > 0.155.0

Visual impairment (cataract)

> 0.10.5-2.0Detectable opacities

Sv/year for many years

Sv single brief exposure

Effect

IAEA 3 : Biological effects of ionizing radiation 49

Whole body response: adult

Acute irradiation syndrome Chronic irradiation

syndrome

Sur

viva

l tim

e

Dose

Steps:

1. Prodromic (onset of disease)

2. Latency

3. Manifestation

Lethal dose 50 / 30

BONE MARROW GASTRO

INTESTINAL

CNS(central nervous

system)

1-10 Gy

10 - 50 Gy

> 50 Gy

•Mechanism: Neurovegetative disorder

•Similar to a sick feeling

•Quite frequent in fractionated radiotherapy

Threshold Doses for Deterministic Effects

• Cataracts of the lens of the eye 2-10 Gy

• Permanent sterility

• males 3.5-6 Gy

• females 2.5-6 Gy

• Temporary sterility

• males 0.15 Gy

• females 0.6 Gy

Severity ofeffect

dose

threshold

Symptoms of Acute Radiation Sickness

Three categories (E. Hall, 1994) Hemopoietic: 3-8 Gy LD50/60

radiation damages precursors to red/white blood cells & platelets

prodromal may occur immediately symptoms: septicemia, survival mixed examples include Chernobyl personnel (203 exhibited

symptoms, 13 died)

Symptoms, continued Gastrointestinal : >10 Gy

radiation depopulates GI epithelium (crypt cells) abdominal pain/fever, diarrhea, dehydration death 3 to 10 days (no record of human survivors above 10

Gy) examples include Chernobyl firefighters

Cerebrovascular : > 100 Gy death in minutes to hours

Delayed Effects

SOMATIC: they affect the health of the irradiated person. They are mainly different kinds of cancer (leukemia is the most common, with a delay period of 2-5 years, but also colon, lung, stomach cancer…)

GENETIC: they affect the health of the offspring of the irradiated person. They are mutations that cause malformation of any kind (such as mongolism)

RADIATION PROTECTION Based on two components.

A) JUSTIFICATION. B) OPTIMIZATION.

JUSTIFICATION:-

Applications of ionising radiation are only justified when they provide a net benefit with minimization of risks of radiation for people.

GUIDELINES FOR REFERRING PHYSICIANS:-

1) Repeating investigations which have already been done: For example at other hospital, in an outpatient department, or in an accident and emergency department. HAS IT BEEN DONE ALREADY? Every attempt should be made to get previous films.

2) Investigation when results are unlikely to affect patient management:

The anticipated 'positive' finding is usually irrelevant, e.g. degenerative spinal disease (as 'normal' as white hairs in old age) or because a positive finding is so unlikely. DO I NEED IT?

3) Investigating too often:-i.e. before the disease could have progressed or resolved or before the results could influence treatment. DO I NEED IT NOW? Or some clinicians tend to rely on investigations more than others. ARE TOO MANY INVESTIGATIONS BEING PERFORMED?4) Doing the wrong investigation:- Imaging techniques are developing rapidly. It is often helpful to discuss an investigation with a specialist in clinical radiology or nuclear medicine before it is requested. IS THIS THE BEST INVESTIGATION?5) Failing to provide appropriate clinical information & questions that imaging Investigation should answer. Deficiencies here may lead to the wrong technique being used (e.g. the omission of an essential view). HAVE I EXPLAINED THE PROBLEM?

OPTIMIZATION:-

Once a practice is justified, the exposure to ionising radiation should be kept as low as reasonably achievable (ALARA).

FUNDAMENTAL PRINCIPLES OF RADIATION PROTECTION:

1. Distance.2. Exposure time.3. Barriers & Shielding.

DISTANCEINVERSE SQUARE LAW:Intensity of radiation is inversely proportional to the square of the distance from the source of radiation. In equation form:

For Example: If thedose is 9 R at 3 feet, stepping back to a distance of 6 feet will cause the dose to decrease to 2.25 R.

57cm from x-ray source 50cm from x-ray source

EXPOSURE TIME The amount of radiation received is proportional to

the length of the exposure time. Minimized by conducting procedures as quickly as possible. For Example, using short bursts of fluoroscopy. Employing image intensifiers & Intensifying screens. Using high kVp , low maS techniques.

BARRIERS & SHIELDING The most commonly used protective material is lead.

It has a double advantage of high density and high atomic number.

Lead equivalent: it is the thickness of lead which provide the same degree of protection as the material.

ROOM SHIELDING: Should be located as far as away from areas of high

occupancy and general traffic. Wall on which primary beam falls should not be less

than 35 cm thick brick or equivalent. Shielding of 1.7mm lead (23 cm brick) in front of doors

& windows of x-ray room.

X-RAY CONTROL ROOM: Walls & viewing windows of control booth should have lead equivalent of 1.5 mm.

Distance between control panel & X-ray unit / chest stand should be minimum 3 meters.

PATIENT WAITING ROOM:

Provided outside X-ray room a proper warning signal when unit is in use.

Warning devices may include audible and visual signs.

LEAD APRON:- Typically thickness of 0.5

mm lead equivalent is used.

Weight ranges from 2.5 to 7 kg.

Should cover much of red bone marrow & breast.

LEAD GLOVES: Lead salts or metallic lead

are added to rubber or plastic.

Lead equivalent of these is about ¼ mm.

LEAD GLASS: Made by adding lead salts to silicates , in the

manufacturing of glass. It is acceptably transparent and a better protective

material. Contains 60% of lead by weight.

GONADAL SHIELDING: Must be 0.5 mm of lead. Must be used when gonads will lie within 5 cm of the

collimated area. Separate male vs. female shielding available.

LEAD GLOVES

LEAD GLASSES

THYROID COLLER

OVARIAN PROTECTION

MALE GONADAL SHIELD

Have standard projections for specific indications. Additional views - on a case-by-case basis Use PA projections, where practical, for chest and spine

radiographs. Avoid repeating exposures. Use safe exposure factors – high KVp and low mAs technique. Never stand in the primary beam.Always wear protective apparel when not behind a

protective barrier. Always wear a radiation monitor and position it outside the

protective apron at collar level. The person holding the patient must wear protective apron

and if possible gloves. Always collimate to smallest field size appropriate to

examination.

RADIATION MONITORING DEVICESNon-Self Reading Devices:

1) FILM BADGES: Consist of a small dental–sized film wrapped in light proof

paper and mounted in a holder filled with metallic filters of different thicknesses.

2) THERMOLUMINESCENT DOSIMETERS (TLD): They are used to measure external individual whole body doses from X-rays , beta rays & gamma radiation. It consists of a TLD card loaded in a cassette (card holder ) having suitable metallic & plastic filters.

TLD Ring or Finger badges:

Ring or finger badges are worn by fluoroscopists & interventional radiologists who usually receive high doses to their extremities.

The ring dosimeter contains a small radiation-sensitive lithium fluoride crystal.

SELF READING DEVICES:Real time dose information available

Needs frequent Calibration checks

Can be taken from hospital to hospital. Good for visiting consultants surgeons, anesthetists, urologists, gastroenterologists etc.

Summary

Ionizing radiation use should be only used when benefit outweighs possible risks.

Every examination should be justified. Optimized protocols for lowering patient dose

without affecting accurate diagnosis should be done.

Use all kinds of radiation protection during work...It's your life.!

IAEA 3 : Biological effects of ionizing radiation 75

Where to Get More Information (1)

• The 2007 Recommendations of the International Commission on Radiological Protection, ICRP 103, Annals of the ICRP 37(2-4):1-332 (2007)

• UNSCEAR 2008 Report to the General Assembly, with scientific annexes, United Nations Scientific Committee on the Effects of Atomic Radiation, United Nations, Vienna, Austria, 2008

• Avoidance of radiation injuries from medical interventional procedures. ICRP Publication 85. Ann ICRP 2000;30 (2). Elsevier

Avoidance of radiation injuries from medical interventional procedures. ICRP Publication 85. Ann ICRP 2000;30 (2). Pergamon