Safe Use of Analytical X-ray Equipment

1. Safe Use of Analytical X-ray Equipment

2. Part 1: The Effect of Ionising Radiation on Living Organisms and Dose

3. This part of the slide show will: • Examine the effect of ionising radiation on living organisms (X-rays are ionising radiation) • Describe units of exposure and dose NB: The following discussion covers general principles of the interactions and is intended to provide a background. Please bear in mind that the X-rays used in X-ray crystallography while low energy (8-9 keV) are capable of delivering a considerable dose.

4. Interaction of X-rays with Matter X-rays are classified as penetrative radiation The penetration of X-rays (or conversely the amount of attenuation) is a function of: •  energy of the x-ray • atomic number of irradiated matter (Bone will absorb low energy x-rays more than muscle) • thickness of irradiated material • density of irradiated material

5. Attenuation of X-rays X-rays are attenuated as they pass through matter The degree of that any given material is able to attenuate x-rays is a function of its atomic number and its density Lead is chosen as a shielding agent because of its high atomic number, its relatively high density and because it interacts with x-ray radiation such all the x-ray energy is absorbed by the Photoelectric effect

6. Effect of Ionising Radiation on Living Organisms Effect of Ionising Radiation at a Molecular Level • When molecules in cells become ionised there a number of effects such as disrupted bonds, alteration of the tertiary and quaternary structure and by crosslinking which in turn damages cells. • Most damage is caused by the generation of hydroxyl free radicals

7. Effect of Ionising Radiation Effect of Ionising Radiation at a Molecular Level cont’d Free radicals are generated by radiolysis of water. 2H20 H2O+ + H20- H2O+ OH. + H+ Hydroxyl radicals react with other molecules (such as DNA) damaging them. Note that the indirect effect is responsible for a significant proportion of cell damage

8. Effect of Ionising Radiation on Tissues and Cells Cellular Radiosensitivity (Law of Bergonne and Tribondeau) 1.Rapidly dividing tissue is more radiosensitive 2. Rapidly growing cells are more radiosensitive 3. Younger and more immature cells are more radiosensitive 4. Mature cells are less radiosensitive NB: Dividing cells are more radiosensitive. This is why radiotherapy is effective on rapidly dividing tumor cells. Unfortunately rapidly dividing cells such as bone marrow, gut epithelium and hair follicles are also radiosensitive Organ toxicity The lens of the eye is particularly sensitive

9. Effect of Ionising Radiation on Humans The effects of ionising radiation are classified on human in two broad categories: • Deterministic • Stochastic

10. Effect of Radiation on Humans Deterministic Effects These effects have thresholds above which damage occurs and effects are then dose dependent e.g. lens opacification, burns, hair loss. Determinisitic effects like the burns below suffered by those who put their hands in the path of a x-ray beam are relatively easy to avoid

11. Effect of Radiation on Humans Stochastic Effects • Mutational, non-threshold effects in which the chance of occurring rather than the severity are dose dependent. • These affects are not predictable e.g. cancer • Note that stochastic effects are not predictable and give rise to the notion that there is no absolutely safe dose and the concept of ALARA.

12. Ionising Radiation and ALARA • ALARA means keeping dose “As Low As Reasonably Achievable” • Reducing dose wherever practicable reduces the probabilities associated with stochastic effects • ALARA principles guide the periodic scanning of x-ray equipment for scatter and leakage as well as following the time and distance rules

13. Part 2: Units of Exposure and Dose

14. This part of the slide show will explain units of exposure and dose for ionising radiation The Sievert is the most relevant unit and is a measure of the health effect of ionizing radiation on the human body.

15. Units of Radiation Exposure and Dose • Exposure (unit is the Roentgen) • Absorbed dose (unit is the Gray) • Dose Equivalence (Unit is the Sievert) Dose Equivalence takes into account the relative biological effectiveness of different types of ionising radiation to damage human tissue

16. Exposure • Unit is Roentgen • Amount of x-rays that will cause 1 gram of air to absorb 86.9 ergs • Useful for gamma and x-rays only

17. Absorbed dose • SI Unit is Gray (Gy); old unit is rad • Dose absorbed by the irradiated material accompanied by 1 joule (100 ergs) of energy being absorbed. • Absorbed dose is independent of the type or energy of ionising radiation

18. Dose Equivalence • Dose equivalence takes into account the effectiveness of the radiation to damage human tissue • Unit is Sievert (Sv); old unit is rem • Dose Equivalence is the product of the Dose (Gray) multiplied by a Radiation Weighting Factor (WR) • Dose Equivalence = D x WR Radiation Weighting factors (WR) are approximately: Alpha particles = 20 Protons, neutrons = 10 Beta particles = 1 Gamma rays and x-rays = 1

19. The Sievert takes into account the Biological Effectiveness of the radiation It can be thought of the absorbed dose of any radiation that produces the same biological effect as 1 Gray of therapeutic x-rays For example: If 2.5 Sieverts of radiation are required for a given biological effect – then this could be delivered by 2.5 Gray of therapeutic x-rays or 0.25 Gray of neutrons Explanation: Neutrons are 10 x more effective at producing the same biological effect (ie: have a Weighting Factor of 10) and hence 1/10 effective dose of neutrons is required for the same biological effect as for x-rays.

20. Prescribed Limits for Dose Equivalence • The ICRP (International Commission for Radiation Protection) is an international non-governmental organisation providing recommendations and guidance on ionising radiation protection based on current scientific evidence

21. ICRP Prescribed Limits per annum Members of public 1 mSv per annum above background 5 mSv to eye 20 mSv to hands Radiation workers 20 mSv per annum above background 150 mSv to eye 500 mSv to hands Pregnant women must receive no more than 2mSv during the course of pregnancy

22. Note that: • ICRP Exposure limits for ‘Members of the Public’ including are deliberately set with large margins of safety taking into account vulnerable persons (pregnant women, babies, the aged, infirmed). • University staff members and students are considered themselves Members of the Public for the purposes of setting exposure limits • Users of analytical x-ray equipment should not receive any measurable dose when operating this equipment.

23. Background Dose • Background dose in NZ is approx 1.8 mSv per annum • Background dose depends on activity • Airline crew on international flights are the most occupationally exposed group in NZ and receive 6-8 mSv per annum

24. Background Dose (or Exposure to Ionising Radiation is a Fact of Life) • Cosmic radiation – approx 300 microSieverts per annum at sea level • Dose from cosmic radiation doubles for every 1500 meters above sea level • Moving up a hill 35m increases annual background dose by 10 microSieverts per annum • Moving from wooden house to brickhouse may increase background dose by 100 microSieverts per annum

25. Typical Dose Airplane travel = 5 microSv/hr Dental x-ray (bitewing) = 12 microSv Dental x-ray (panorama) = 90 microSv Chest X-ray = 50 microSv Mammogram = 0.7milliSv Barium Enema = 7 milliSv CT Scan (abdomen) = 10 milliSv CT Scan (whole body) = 20 milliSv

26. Effective dose 0.5 Sv = Increased lifetime dose in Chernobyl Effective dose over 1-2 Sv = Haemopietic Syndrome depression of immune function Effective dose over 2-3 Sv = hair loss Effective dose 5 Sv = Median Lethal Dose

27. Radiation Risk • ICRP data – 1 mSv increases lifetime cancer risk of 1/20,000 • Lifetime cancer risk for whole population is 1/4

28. Applicability to Analytical X-ray Equipment • While analytical x-rays are low energy, the x-ray intensity or flux is very high and capable of delivering a lot of energy

29. 50kV Mo x-ray tube at 40 mA will deliver 7000 Sv/sec! 3.5 Months 1 Month ICRP limit is 500 mSv to hands per year 14,000 x Annual limit received in one second!

30. This is why: • Analytical x-ray instruments are closed beam and are surrounded in a housing and lead glass windows to protect the users from the primary beam and x-ray scatter. • The instruments are interlocked so that the shutter is closed and x-ray beam is stopped when glass windows are opened. • The local rules are to be obeyed. • Only authorised maintenance licensees carry out repairs. • Any malfunction must be reported immediatel.

31. Part 3: Safe Use of the X-ray Equipment and Legal Requirements

32. Part 3 of the slide show will: 1. Give the 4 fundamentals of x-ray safety 2. Explain the legal obligations as part of the use of x-rays. 3. Explain the safety features incorporated into modern analytical x-ray equipment.

33. Safety with Ionising Radiation In order to follow ALARA principle there are Four Principles of Ionising Radiation Safety: 1. Minimise Exposure Time 2. Maximise Distance from Source 3. Use Correct Shielding 4. Follow Manufacturers Instructions and Local Rules

34. Applicability to Analytical X-ray Equipment Time and Distance • Analytical X-ray equipment has highly collimated beams and extensive shielding but because dose is a function of time you should as a rule should minimise the time spent very close to any source of ionising radiation

35. Shielding • Only authorised maintenance licensees may over-ride interlocks and remove and install shielding • Authorised maintenance licensees must then check and document that they have reinstated shielding and interlocks correctly • Dosimetry is conducted periodically to verify that the shielding is intact and is functioning as intended

36. Follow Local Rules and Manufacturers Instructions • Only authorised operators of X-ray equipment who are familiar with safe operation of machine use the apparatus. • Authorised users must follow licensee and manufacturers instructions • Authorised users must report any anomalies or any equipment malfunction to the license holder immediately

37. Legal Obligations • The Office of Radiation Safety (ORS) is the New Zealand statutory body which regulates use of radioisotopes and irradiating apparatus. • All irradiating equipment must have a current licence-holder in charge of the apparatus. • All use of irradiating equipment must be under the supervision (ie physical presence of license holder) or operate the equipment under the liccensees instruction.

38. Specific legal requirements for the Use of Analytical X-ray Equipment • There must be a current licence holder in charge • All users are authorised by licence holder • All users are properly trained (training is documented) • Access to the machine is restricted • Prominent warning signs on doors and equipment • Users must observe all local rules

39. There is a log of authorised users and log of use and repairs – you must fill out the machine log • Any anomalies or any equipment malfunction must be reported to the license holder immediately • All emergency procedures for the equipment must be observed • Equipment is periodically monitored for scatter and X-ray leakage and repairs are undertaken only by authorised persons

40. Analytical x-ray safety features: • Analytical x-ray instruments are enclosed to protect the users from primary beam and scatter. • Beams are highly collimated to prevent unwanted exposure and reduces scatter. • Any opening door/windows are interlocked to x-ray shutter. • Interlocks are fail safe (i.e. wired in series with x-ray generator so if the interlocks fail, the generator will not be powered) • Warning lights are fail safe (i.e. in series with x-ray generator as above)

41. Analytical X-ray Unit Safety Features Interlocked leaded glass panels protecting from primary beam and scatter Warning lights

42. End of Slideshow You should now undertake the test