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Radioprotection - basics of radiobiology -

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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Radioprotection - basics of radiobiology -

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  1. Radioprotection - basics of radiobiology - 3 LF UK Praha Dept. of Radiology 2011

  2. 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

  3. Stochastic effect Deterministic effect Ef Ef D D • without threshold with threshold • linear non-linear • genetic effects - damage of tissues • - carcinogenesis - radiation sickness

  4. 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

  5. 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

  6. Irradiation of a man on earth surface CR 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)

  7. 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.

  8. 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 )

  9. LEGISLATIVA NA POLI RADIAČNÍ OCHRANY 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

  10. DIAGNOSTIC and INTERVENTIONAL • RADIOLOGY • basic approach - ALARA • exposure should be As Low As Reasonably Achieveble • diagnostic benefit >> radiation risk • Principles : -justification • - optimalisation

  11. 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

  12. 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

  13. Czech referral guidelines

  14. 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

  15. Classification of effective doses for different radiological examinations Class 0 – IV.

  16. Examples of effective doses in common RDG exams

  17. Equivalent doses : Rx of thorax = 1

  18. 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

  19. 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 !

  20. Czech standard protocols of CT examinations

  21. 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

  22. Personal protectors - patient and personnel aprons Protectors are shielding against secondary rays only ! Radiologists and radiographers should never enter in a primary beam !

  23. 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.

  24. Protective dosimetry - personnel film dosimeter ring dosimeter obligatory interventional radiology

  25. 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)

  26. 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)

  27. 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

  28. X-ray examination should bring MAXIMUM CLINICALLY RELEVANT INFORMATION FOR THERAPEUTIC DELIBERATION WITH MINIMAL IRRADIATION AND FOR AN ACCEPTABLE PRICE

  29. 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 )

  30. Thank you for attention !

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