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
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
- gradaion of deterministic effects
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
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
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
In radiodiagnostics we protect against external sources of irradiation only, unlike in nuclear medicine
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.
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
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
Czech referral guidelines
for different radiological examinations
Class 0 – IV.
Rx of thorax = 1
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
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 !
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
Protectors are shielding against secondary rays only !
Radiologists and radiographers should never enter in a primary beam !
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.
film dosimeter ring dosimeter
obligatory interventional radiology
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)
Effective dose Risk
lower than 0,1 mSv negligible
0,1 – 1 mSv minimal
1 – 10 mSv very low
10 – 100 mSv low
MAXIMUM CLINICALLY RELEVANT INFORMATION FOR THERAPEUTIC
DELIBERATION WITH MINIMAL IRRADIATION AND FOR AN ACCEPTABLE PRICE
from different causes ( in days )
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 )