hazards & protection

Radiation Hazards and Protection

April 8, 2023 1Dr Saad Wahby Al Bayatti

X- ray Dose Measurements

X- ray Dose Units


Radiation Absorbed Dose

• This is a measure of the amount of energy absorbed from the radiation beam per unit mass of tissue

• Unit of measurement:• SI unit : Gray, (Gy) measured in joules/kg• original unit : rad, measured in ergs/gm• 1 Gray = 100 rads


Equivalent Dose

• A measure which allows comparison between different types of radiation in regard to their absorbed doses in the body (RBE radiobiological effectiveness)

• Unit of measurement (SI unit) : Sievert (Sv)• subunits : millisievert (mSv) ( ×1/1 000)• : microsievert ( µSv) ( ×1/1 000 000)• original unit : rem• 1 Sievert = 100 rems


Quality Factor (Q)

• Represents the biological effects of each type of radiation:

• X- rays, gamma rays and beta particles Q = 1

• Fast neutrons protons Q = 10• Alpha particles Q = 20


Equivalent Dose

• equivalent dose = radiation absorbed dose (Gy)× Q

• Since Q for x -ray = 1, then

equivalent dose = radiation absorbed dose

(Sv) = (Gy)


Effective Dose

• Each body tissue is affected differently by radiation

• Effective dose: This is a measure that allows doses from different investigations of different parts of the body to be compared , by converting all doses to an equivalent whole body dose


Weighing Factor (W)

• Measures the radiosensitivity, i.e.the risk of the tissue being damaged by radiation.

• The higher the damage, the higher is W


Weighing factors for different body tissues

Tissue Weighing factor

Testes and ovaries 0.20

Red bone marrow, colon, lung, stomach

0.12

Breast, bladder, liver, thyroid 0.05

Bone surfaces , skin 0.01

Remainder 0.01


Effective Dose

• Effective dose = equivalent dose × weighing factor

= radiation absorbed dose(Gy)×Q ×W• SI unit : Sievert (Sv)• subunit : millisievert (mSv)

• Effective dose (whole body) = sum of W


Absorbed dose

Multiplied by a factor to reflect harm by a specific radiation

Equivalent dose

Multiplied by a factor to reflect sensitivity of a specific tissue

Effective dose, commonly called “dose”


Effective doses X -ray examination

X- ray exam. Effective dose (mSv)• CT cest 8.0• barium meal 7.7• lumbar spine 2.2• CT head 2.0• skull 0.1• chest 0.04• OPG 0.007• 2 intra oral films (E speed) 0.002


The frequency of taking films is based on the following factors:

1. Patient’s oral hygiene 2. Caries activity 3. Dental history 4. Reliability of patient 5. ADA Guidelines

ADA Guidelines

Full-mouth Series 1 - 5 yearsBitewings 6 months - 3 yearsPanoramic 1 - 5 years

Biological Effects of X-ray


Radiobiology

The response of living systems to ionizing radiation

Biological Effects of X-ray

• X-Rays interact with living tissues and can cause

biological changes.

• These changes are mediated directly by excitation

or ionization of atoms or indirectly as a result of

chemical changes occurring near the cells.

• Affected cells may be damaged or killed.


Biological Effects of X-ray (cont’d)

• Genetic effects involve chromosomal damage or

mutation in the reproductive cells and will affect

future generations.

• Somatic effects involve damage to other tissues and

result in changes within the individual’s lifetime

(e.g. radiation burns, leukemia).

• Radiation is a particular hazard because its effects

are painless, latent and cumulativeApril 8, 2023 18Dr Saad Wahby Al Bayatti

Incoming photon

Excited electron

Excitation


Incoming photon

Ejected electron

Photon

Positive Ion

Ionization Photon


Ionization

The process of removing an electron from an electrically neutral atom to produce an ion. An ion is an atom or subatomic particle with a positive or negative charge.

Ionization negative ion

positive ion

AttenuationReduction of x-ray beam intensity (that reaches film) by interaction with matter.

1. Coherent scattering

2. Compton scattering

3. Photoelectric absorption

Coherent Scattering

Low-energy x-ray interacts with outer-shell electron and causes it to vibrate briefly. Scattered x-ray of same energy as primary x-ray is then emitted, going in a different direction than primary x-ray. Electron not ejected from atom. (No ionization).

Coherent Scattering

Compton Scattering

Outer shell electron ejected (Ionization)

Scatter radiation results

Occurs majority of the time

30% of scatter exits head

recoil electron

scattered x-ray

Compton Scattering

primary x-ray

The primary x-ray strikes an outer-shell electron, knocking it out of its orbit (ionization). The primary x-ray loses some of its energy and continues in a different direction as a scattered x-ray.

Inner-shell electron ejected (Ionization)

Complete absorption

Photoelectric Absorption

photoelectron

primary x-ray

Photoelectric Absorption

The primary x-ray strikes an inner-shell electron, knocking it out of its orbit (ionization). The x-ray loses all of its energy and disappears. There is no scatter.

Dose-Response Curves

threshold

linear

non-linear

non-threshold

Res

pons

e

Dose

Linear: the response is directly related to the dose.

Non-linear: the response is not proportionate to the dose.

Threshold: the dose at which effects are produced; below this dose, there are no obvious effects.

Non-threshold: any dose produces a response.

Critical Molecule (Target)

DNA

Radical

Atom or molecule that has an unpaired electron in the valence shell, making it highly reactive. (Most damaging).

Mutations

Cell death

Sublethal injury

Biologic Effects

DNA altered; cell function altered or development changed. It is unclear which critical lesion/s in DNA may lead to cancer.

Mutation

Normal

Mutation

Loss of capacity for mitosis

Cell Death

Cellular Repair

1. Damage to biologic molecules (single-strand break of DNA)

2. Removal of damaged section by cell enzymes

3. Placement of new material by other cell enzymes

Radiation Effects Influenced by:

Total dose

Dose rate

Total area covered

Type of tissue

Age

Sources of Radiation


Sources of Radiation

• Natural background radiation

- cosmic rays

- gamma rays from rocks & soil 87%

- ingested radioisotops in certain foods

- radon decay products (granite )• Artificial background radiation

- fallout from nuclear explosions > 1%

- radioactive waste • Medical and dental diagnostic radiation 12% • Occupational exposure > 1%


Biologic Effects Of Ionizing Radiation

Stochastic• The probability of occurrence of the change, rather than its severity, is

dose dependant • All or non, the person either has the condition, or not• No threshold

e.g.• Radiation induced cancer, greater exposure of population to radiation

increases cancer probability, but not its severity

Deterministic• The severity of response is proportional to the dose• Occur in all people when the dose is large enough• There is a dose threshold below which the response is not seen

e.g. • Oral effects after radiation therapy• Radiation sickness after whole body radiation


Radiation Hazards


Radiation Hazards

N u clera r b o m sn u eclea r rea c to rs lea ks

W h o le b o d yra d ia tio n

M ed ica l(d ia g n o s tic & th era p u tic )

D en ta lX - ra ys

S p ecific a reara d ia tio n

R a d ia tio n exp o su re


Specific Versus Whole-Body Radiation


Radiation Hazards

Ind irec t D irec t

Som a ticA ffec ts in d iv idua l

N o e f fec t o n o f fsp r ing

G ene ticD o no t a f fec t ind iv idu ia l

O ffsp r ing is a f fec ted

R ad ia tion d am age


Radiation Hazards Direct Damage

RH + Radiation R+ + H

+ + e

-

R + Dissociation

R + X + Y

Cross-linking

R + + S RS


Radiation Hazards Direct Damage

Radiation

• DNA /RNA molecule nuclear acid breakdown• Nuclear acid breakdown Somatic cells radiation induced malignancy Genetic cells radiation induced congenital abnormality


Radiation Hazards (indirect damage)

Water Hydrolysis

• H 2 O H + + OH -

• H + + H

+ H 2

• OH - + OH

- H 2 O 2

Radiation


• H2O2 + DNA Molecular

breakdown• H2O2 + Proteins

• Molecular breakdown Cell damage

Radiation Hazards (indirect damage)

Water Hydrolysis


Radiation Hazards

D irec tD N A /R N A h it

R a d ia tio n in d u ced m a lig n a n cy

In d irec tH 2 O 2 fo rm a tio n

T O X ICb rea k d o w n o f la rg e m o lecu les (p ro tien s /D N A )

S o m a tic

R a d ia tio n d a m a g e


Radiation Hazards

D ir e c tD N A /R N A h it

R a d ia tio n in d u c e d c o n g e n ita la b n o r m a lity

I n d ir e c tH 2 O 2 fo r m a tio n

T O X I Cb r e a k d o w n la r g e m o le c u le s ( p r o te in s / D N A )

G e n e tic

R a d ia tio n d a m a g e


Factors Affecting Radiosensitvity

• Dose: the amount of radiation received. The higher the dose, the greater is the effect (consider the threshold)

• Dose rate: the rate of exposure. e.g. a total dose of 5Gy can be given as- 5Gy/min (single dose) is more destructive - 5mGy/min(fractionized), less destructive, injured cells can recover

• Oxygen: the higher the O2 level in irradiated cells, the greater is the damage. (H2O2 formation)

• Linear Energy Transfer (LET): the rate of loss of energy from a particle as it moves in its track through matter (tissue)

e.g. alpha particles vs. X-ray


X- ray Protection


X- ray Protection

Follow ALARA , keep exposure

A = As

L = Low

A = As

R = Reasonably

A = Achievable


P a tien t S ta ff p u b lic

X - ra y p ro tec tio n


X- ray ProtectionPatient

• Radiographs are only taken when necessary • Number, frequency and type of radiographs is the

responsibility of the dentist• Use high output DC x- ray generators• Minimum kilovoltage should be 60kV• Minimum milliamperage should be 8 mA • Minimum filtration should be 1.5 mm Al



• Maximum Beam diameter should be 7 cm (circular beams)

• Use rectangular collimation for intra oral films• Minimum target – skin distance should be 20 cm• Accurate timer • Use open- ended lead lined cylindrical cones

(PID)• Do not use close ended pointed plastic cones



• Use high speed films (D or E ) • Use film holders and beam-aiming devices • Avoid retakes, master radiographic

techniques • Avoid retakes, master film processing

techniques• Use lead aprons • Use thyroid collarsApril 8, 2023 61Dr Saad Wahby Al Bayatti

Lead Aprons


Lead Apron/Thyroid Collar

Psychology

Protection

Adult Patient’ s Lead apronwith a thyroid collar

Separate thyroid collar


Child Patient’ s Lead apronwith and without thyroid collar


https://www.denmedpro.com/secure/images/products2/126343.jpg

Operator’s Lead apron


Proper placement of the Lead apron with a thyroid collar


Correct way of hanging the Lead apron


Lead apron Without a thyroid collar


Correct way of hanging lead apron and thyroid collars


Lead apron hangers


X- ray ProtectionStaff

• Never hold the x- ray head during exposure• Never hold the film during exposure• Never stand in the path of the primary beam• Stand behind a lead barrier (2 mm thickness)• Watch the patient through leaded glass during

exposure • Stand minimum 2 M from the x-ray beam behind

the patient’s head


X- ray ProtectionPublic

• Warning/Informative signals to indicate hazardous x- radiation

• Patients should be seated away from x- ray rooms

• Patients are not allowed to wait in corridors next to x- ray rooms


Open –ended cylindrical

Close ended plastic

7 cm

7 cm


Mobile lead barriers April 8, 2023 76Dr Saad Wahby Al Bayatti

Open-end cylindrical coneClose-end pointed cone

√X


Rectangular modifications for an Open-end cylindrical cone


Rectangular collimators

Circular collimators

Area of exit of the x-ray beam

Area of exit of the x-ray beam

Metal shield


Long cylindrical Open-end cone

Short cylindrical Open-end cone

Long rectangular cone

Short rectangular cone


Patient

90-135 o o

90-135

X- ray head

90o

90o

180o

Operator Safe

position

Operator Safe

position

Scattered rays Scattered rays

DangerDanger

Safe operator’s positionNo barrier used


Patient

90-135 o

o

90-135 90

o

90o

180o

Operator’sSafe position

OperatorSafe

position

Scattered rays

Scattered rays

X- ray

head

Danger

Danger

Safe operator’s positionNo barrier used


1 M

2 M

A

B

Source

Inverse square lawI 1/D

Intensity of radiation at B =1/4 at A

2


Inverse-square law states that the intensity (quantity) of X-ray is inversely proportional to the square of the distance from the source of radiation


2 M minimum.

Operator`

Patient

Danger

X -ray

Safe operator’s position


Operator`

Lead barrier

Using a lead barrier allows less than 2 M distance

X- ray

Patient

Danger


Patient

Operator`

Leaded wall room

Leaded glass

Danger

X- ray


Patients’Waiting rooms

X- ray room

X- ray room

Restricted areas

Restricted areas

Safe patients waiting rooms


hazards & protection

Technology

effective dose effective

dose sv

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dose gyq

thenequivalent dose

byradiation effective