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Radioprotection - basics of radiobiology -. 3 LF UK Praha Dept. of Radiology 2011. X – rays - electromagnetic ionizing radiation. Photons of X-rays are ionizing the irradiated matter

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- basics of radiobiology -

3 LF UK Praha Dept. of Radiology 2011

X – rays - electromagnetic ionizing radiation

Photons of X-rays are ionizing the irradiated matter

By physical and chemical mechanisms they induce biological effects.


There are two basic kinds of biological effects :

Stochastic ( or random ) effects on the cellular level :

„ target theory“

Deterministic ( or nonstochastic ) effects on the tissue


Stochastic effect Deterministic effect





  • without threshold with threshold

  • linear non-linear

  • genetic effects - damage of tissues

  • - carcinogenesis - radiation sickness

Example: skin reaction on irradiation by ionizing radiation

- gradaion of deterministic effects

B Ef

First threshold : erytema dose – hyperaemia – reddness - a

Second threshold : epilation dose – pigmentation and epilation - b

Third threshold : necrotic dose – damage of skin with necrosis - c

Units of dose

Physics absorbed dose :

Gray ( Gy ) = J/kg = 100 rad

Radiobiology and radiation protection effective dose

Sievert ( Sv ) = Dabs . QF = 100 rem


Dose equivalent or effective dose enables to compare biological effects of different kinds of ionizing radiations.

QF (quality factor) equals 1 for X-rays and gamma rays.

Therefore by X-rays 1 Gy = 1 Sv.

Doses in radioprotection are expressed in Sieverts

Doses delivered in radiotherapy are expressed in Grays

Irradiation of a man on earth surface


Natural sources : radon, natural radionuclides, cosmic rays : 83,6 %

Arteficial sources : medical exposures, nuclear plants, radioactive fallout,

professional exposures : 16,4 %

Medical exposures: Dg and Th RDG : NM = 9 : 1 CR yearly ~ 1 mSv

CR: average year exposure of inhabitant ~ 3,3 mSv


Radiation protection in radiodiagnostics

In radiodiagnostics we protect against external sources of irradiation only, unlike in nuclear medicine

  • Basic rule of radioprotection:

  • Eliminate entirely the deteministic effests

  • Minimize the stochastic effects

Note: In radiotherapy we use the deteministic effects to kill the malignant cells, but the damage to the neighbouring tissues should be as small as possible.

Radioprotection in radiological departments

is concerning

patients and medical personnel

Each country has it own legislation on radiation

protection, implemented from EURATOM regulations

and control organs – State Office of Nuclear Safety

EU: EC Dir. 97/43/EURATOM ( Medical Exposure Directive )


EU: EC Dir. 97/43/EURATOM( Medical Exposure Directive )

ČR: zákon č. 18/1997 Sb., novela č. 13/2002 Sb.

" atomic law"

vyhláška SÚJB o radiační ochraně č. 184/1997 Sb.

novela č. 307/2002 Sb.

Directive on radiation protection



  • basic approach - ALARA

  • exposure should be As Low As Reasonably Achieveble

  • diagnostic benefit >> radiation risk

  • Principles : -justification

    • - optimalisation

Principle of justification

Diagnostic gain from radiological examination must be greater then possible risk or radiation

All examinations utilizing X-rays – conventional radiodiagnostics

and CT – must be correctly indicated

Responsible is an indicating physician,

but radiologist shares responsibility as well

EU : Referral guidelines for imaging

Věstník MZd 2003

Czech referral guidelines

  • The indication to X-ray examination should consider also the age and gender of a patient and radiosensitivity of irradiated tissues

Czech referral guidelines

Referral guidelines

  • Appraisal of indicated method – recommendation :

    • 1. Indicated

    • 2. Indicated as specialised examination

    • 3. Non indicated as first examination

    • 4. Non indicated in routine

    • 5. Non indicated at all

Classification of effective doses

for different radiological examinations

Class 0 – IV.

Examples of effective doses in common RDG exams

Equivalent doses :

Rx of thorax = 1

  • Principle of optimalisation

  • Medical irradiation – exposure – must be as low as

  • technically feasible to obtain the optimal image

Exposure values should be set correctly in order to minimize the irradiation of the patient and of the personnel.

Regular controls of all X-ray sources by the radiographers and by licensed technicians to ensure their stability and reproducibility

Technical standards of different examinations

Proper use of shielding and protective devices

Clinical audit

X-ray examination

Dose is dependent of:

exposition : kV, mA, s

filtration of a primary beam

primary diaphragm – delimitation of the field

sensitivity of the film and of the intensifying screen

distance between the focus of the tube and the skin

Proper development of a film is important as well !

Defective film must be repeated – the dose is doubled !

Czech standard

protocols of CT


X-ray examination room must be shielded in order to eliminate irradiation of persons in the neighbouring rooms and labeled with warning signs

lead or barium plaster - Pb equivalent

Personal protectors - patient and personnel


Protectors are shielding against secondary rays only !

Radiologists and radiographers should never enter in a primary beam !

Dose limits

Defined only for personnel :

Wholebody irradiation – 20 mSv/year

This limit is derived from stochastic effects of the secondary radiations.

Controle: personal film dosimeters – centrally registered

Eye lens - 150 mSv/year

Skin - 500 mSv/year

These limits are derived from deterministic effects.

Protective dosimetry - personnel

film dosimeter ring dosimeter

obligatory interventional radiology

Risk assessment in X-ray exposure

In small doses risk of stochastic effects

- on cellular level -

expressed by effective dose (mSv)

In greater doses risk of deterministic effects

- on tissue level -

expressed by organ dose (mGy)

Risk assessment in radiation exposure depends on many factors

  • Absorbed dose

  • External or internal irradiation

  • Wholebody or localised irradiation

  • Kind of radiation - nonionizing

  • - ionizing ( directly or indirectly)

  • RBE of the respective radiation ( QF )

  • Radiosenzitivity of the respective tissue

  • Other – age, gender (women in productive age)

Risks in small doses exposure radiodiagnostics – stochastic effects

Effective dose Risk

lower than 0,1 mSv negligible

0,1 – 1 mSv minimal

1 – 10 mSv very low

10 – 100 mSv low

X-ray examination should bring



Approximative shortening of a lifetime

from different causes ( in days )

smoking 2400

30 % excess of weight 1560

trafic accidents 700

home accidents 290

accidents at work 55

radon in buildings 50

natural radioactivity 9

medical exposures 6

nuclear reactors accidents 0,02

( WHO 2003 )

Thank you for attention !

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