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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 - PowerPoint PPT Presentation
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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
By physical and chemical mechanisms they induce biological effects.
Radiobiology
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
level
Stochastic effect Deterministic effect
without threshold with threshold
linear non-linear
- genetic effects - damage of tissues
- carcinogenesis - radiation sickness
Ef Ef
D D
Example: skin reaction on irradiation by ionizing radiation
- 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
B Ef
Units of dose
Physics absorbed dose :
Gray ( Gy ) = J/kg = 100 rad
Radiobiology and radiation protection effective dose
Sievert ( Sv ) = Dabs . QF = 100 rem
Note:
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
(2000)
CR
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 EU: EC Dir. 97/43/EURATOM ( Medical Exposure Directive )( Medical Exposure Directive )
LEGISLATIVA NA POLI RADIAČNÍ OCHRANYLEGISLATIVA NA POLI RADIAČNÍ OCHRANY
EU: EU: EC Dir. 97/43/EURATOMEC Dir. 97/43/EURATOM ( Medical Exposure Directive )( Medical Exposure Directive )
ČR: ČR: zákon č. 18/1997 Sb., novela č. 13/2002 Sb.zákon č. 18/1997 Sb., novela č. 13/2002 Sb. " atomic law"" atomic law" vyhláška SÚJB o radiační ochraně č. 184/1997 Sb. vyhláška SÚJB o radiační ochraně č. 184/1997 Sb. novela č. 307/2002 Sb.novela č. 307/2002 Sb. Directive on radiation protectionDirective on radiation protection
LEGISLATIVA NA POLI RADIAČNÍ OCHRANYLEGISLATIVA NA POLI RADIAČNÍ OCHRANY
EU: EU: EC Dir. 97/43/EURATOMEC Dir. 97/43/EURATOM ( Medical Exposure Directive )( Medical Exposure Directive )
ČR: ČR: zákon č. 18/1997 Sb., novela č. 13/2002 Sb.zákon č. 18/1997 Sb., novela č. 13/2002 Sb. " atomic law"" atomic law" vyhláška SÚJB o radiační ochraně č. 184/1997 Sb. vyhláška SÚJB o radiační ochraně č. 184/1997 Sb. novela č. 307/2002 Sb.novela č. 307/2002 Sb. Directive on radiation protectionDirective on radiation protection
DIAGNOSTIC and INTERVENTIONALDIAGNOSTIC and INTERVENTIONALRADIOLOGYRADIOLOGY
basic approach basic approach - ALARA- ALARA exposure should be exposure should be AAs s LLow ow AAs s RReasonably easonably AAchieveblechieveble
diagnostic benefit diagnostic benefit >> >> radiation riskradiation risk
Principles : Principles : -- justificationjustification - optimalisation- optimalisation
DIAGNOSTIC and INTERVENTIONALDIAGNOSTIC and INTERVENTIONALRADIOLOGYRADIOLOGY
basic approach basic approach - ALARA- ALARA exposure should be exposure should be AAs s LLow ow AAs s RReasonably easonably AAchieveblechieveble
diagnostic benefit diagnostic benefit >> >> radiation riskradiation risk
Principles : Principles : -- justificationjustification - optimalisation- optimalisation
Principle of justification
Diagnostic gain from radiological examination must be greater then possible risk or radiation
EU : Referral guidelines for imaging
All examinations utilizing X-rays – conventional radiodiagnostics
and CT – must be correctly indicated
Responsible is an indicating physician,
but radiologist shares responsibility as well
Věstník MZd 2003
• The indication to X-ray examination should consider also the age and gender of a patient and radiosensitivity of irradiated tissues
Czech referral guidelines
Czech referral guidelines
Referral guidelines
Appraisal of indicated method – recommendation :Appraisal of indicated method – recommendation :
1. Indicated1. Indicated2. Indicated as specialised examination2. Indicated as specialised examination3. Non indicated as first examination3. Non indicated as first examination4. Non indicated in routine4. Non indicated in routine5. Non indicated at all5. 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
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
X-ray examination
Defective film must be repeated – the dose is doubled !
Proper development of a film is important as well !
Czech standard
protocols of CT
examinations
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 !
aprons
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
MAXIMUM CLINICALLY RELEVANT MAXIMUM CLINICALLY RELEVANT INFORMATION FOR THERAPEUTICINFORMATION FOR THERAPEUTIC
DELIBERATION WITH MINIMAL DELIBERATION WITH MINIMAL IRRADIATION AND FOR AN IRRADIATION AND FOR AN
ACCEPTABLE PRICEACCEPTABLE PRICE
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 !