Radiation Protection Refresher for Bone Densitometry - PowerPoint PPT Presentation

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Radiation Protection Refresher for Bone Densitometry

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  1. Radiation Protection Refresher for Bone Densitometry Dr. Craig Moore Medical Physicist & Radiation Protection Adviser Radiation Physics Service CHH Oncology

  2. THE PATIENT IS NOT RADIOACTIVE AFTER THEY HAVE HAD AN X-RAY

  3. Medical X-ray Equipment

  4. 1895 - Wilhelm Roentgen-The Start Discovered X-rays on 8th November 1895 1896 - X-ray Department set at Glasgow Royal Infirmary Produced many remarkable radiographs In 1896 medical x-ray diagnosis was also started.

  5. Colles’ fracture 1896 Frau Roentgen’s hand, 1895

  6. First Dental Radiograph • Otto Walkhoff (Dentist - Braunschweig, Germany) • Jan.1896 (<2 weeks after Roentgen announced discovery of X-rays) • 25 minute exposure.

  7. 1 Feb 1896 • Walter Konig (physicist, Germany) • 9 min. exposure

  8. 1896 - First Reports of Injury Elihu Thomson – He immediately saw the dangers of the new radiation but was in a minority. Deliberately exposed a finger for several days to prove the point. Edison’s assistant - hair fell out & scalp became inflamed & ulcerated

  9. MihranKassabian (1870-1910) • Was a medical missionary student and photographer who became one of the most prominent pioneering radiologists of the time. • By 1898 he had become an American citizen

  10. MihranKassabian (1870-1910) • In 1898 he joined the Hospital Corps of the regular army, gaining much experience in x-ray technique, and paid the price • In 1900 he describes the damage to his hands. • He attributed the damage to holding the tube and putting his hands in the beam to reassure the patient. In 1903 he urged his colleagues to discuss ways of avoiding the damage that could be caused.

  11. Sister Blandina (1871 - 1916) 1898, started work as radiographer in Cologne - held nervous patients & children with unprotected hands After 6 months cancer of hand - arm amputated • 1915 severe difficulties of breathing - extensive shadow on the left side of her thorax - large wound on her whole front- and back-side • Died on 22nd October 1916.

  12. What is Radiation? • Wave – an electric part, and a magnetic part • ELECTROMAGNETIC RADIATION • EM radiations spread like waves, over space.

  13. What is Radiation? • Photon – a particle • Absorption of energy occurs in well-defined chunks of energy, known as wave packets or more correctly photons. HOWEVER, RADIATION IS NOT ABSORBED LIKE A WAVE, SO WE HAVE TO DESCRIBE RADIATION AS DESCREET PARTICLES OF ENERGY

  14. Some Basic Physics – The Atom - OuterElectrons (- ‘vly charged)orbiting the nucleus. - - + - • An inner Nucleusmade up of Protons(+’vly charged) and Neutrons (0 - zero charge), jointly known as Nucleons. - -

  15. Ionising Radiation - + Ionising radiations – have the ability to separate electrons from atoms to produce “ions”

  16. Radiation Hazards Why is it dangerous?

  17. Quantifying the Risk - Radiation Dose RADIATION TISSUE • Absorbed Dose (Jkg-1) • Amount of energy deposited per kilogram • Dose to an organ or tissue • Unit is the Gray (Gy) • DOSE TO A CERTAIN PLACE IN THE BODY • Effective Dose (Jkg-1) • This is the average dose to whole body • Unit is the Sievert (Sv) • This gives us the risk of contracting cancer from the x ray exposure • THIS IS THE OVERALL DOSE TO THE WHOLE BODY

  18. Effective dose • Dose “averaged” over whole body • Risk of inducing cancer is proportional to effective dose, e.g. • LD(50,30) = 4 Sv • UK background = 2.3 mSv per year • Legal dose limit for staff working with DEXA = 6 mSv a year. • Dose Investigation Level for DEXA workers = 1.2 mSv/yr (or 0.1 mSv/month) • Never go above 1 mSv/yr • Usually record zero on dose badge

  19. Risks Associated with X rays • Adult Exposure (per 1 mSv) • Fatal cancer (all types) 1 in 20,000 • Fatal leukaemia 1 in 200,000 • Non fatal cancer 1 in 100,000 • Heritable effects 1 in 80,000 • Childhood exposure • Fatal cancer 1 in 10,000 • Foetal exposure • Fatal cancer to 15 years 1 in 33,000 • All cancers to 15 years 1 in 17,000 • Heritable effects 1 in 42,000

  20. Risks from Bone Densitometry Exposures

  21. Prodigy Patient Risks • Patient entrance skin dose • AP spine 0.75mA thin = 12 μGy • AP spine 3mA standard = 47 μGy • AP spine 3mA thick = 105 μGy • Effective dose = 0.01 mSv • Risk of radiation induced cancer = 1 in 2 million (i.e. negligible) • REMEMBER – RISK OF GETTING CANCER IN OUR LIFETIME IS 1 IN 3 • So – RADIATION CANCER INDUCED RISKS ARE RELATIVELY SMALL • NEVERTHELESS: • All exposures must be JUSTIFIED • Doses to patients, and staff, must be As Low As Reasonably Practicable (ALARP principle) .

  22. Prodigy Staff Risks • 3 mA • Edge of couch < 24 μSv/h • 1m from couch < 3 μGy/h • Patient entrance skin dose • AP spine 0.75mA thin = 12 μGy • AP spine 3mA standard = 47 μGy • AP spine 3mA thick = 105 μGy

  23. Prodigy Staff Risks • Use dose constraint of 0.3 mSv a year • Scatter 1m from couch < 3 μGy/h • Scans about 1 minute each • 2500 patients a year • So dose < 3 μGy/h x 2500 x 1/60 = 125μGy = 0.125 mSv • So • Controlled area of 1m from couch OK • No lead glass screen needed.

  24. Pixi • Beam on for 2.5 secs at 50kV then 80kV • Dose at 50cm from unit < 40 μSv/h • Dose to heel ≈ 200 μGy

  25. Pixi Staff Risks • Use dose constraint of 0.3 mSv a year • Scatter 50 cm from couch < 40 μGy/h • Scans about 2.5 seconds each • < 30 exposures a day, • So dose < 40 μGy/h x 30/d x 2.5/3600 x = 0.8 μGy/day < 170 μGy/year =0.17 mSv • So • Controlled area of 50 cm from Pixi OK • No lead glass screen needed.

  26. Calscan • 0.5m controlled area • Heel entrance dose ≈ 240 μGy • Effective dose to patient = 0.2 μSv

  27. Metriscan • Scatter dose < 0.50 μGy per exam at edge of machine • Patient Skin dose < 120 μGy

  28. Recent dose results

  29. Levels of Risk • 1 milli-sievert (1 mSv) • annual public dose limit • patient dose from abdomen X-ray • 1 in 20,000 risk of fatal cancer • Risk of dying on UK road = 1 in 20,000 per year • Risk from chest X-ray = 1 in 1,000,000 • Risk of meteorite killing 1/4 of world population = 1 in 500,000

  30. Everyday non-Occupational Doses • Effective dose from natural background radiation in the UK is approximately 2.2 mSv • SO WE ALL RECEIVE 2.2 mSv EVERY YEAR FROM NATURAL SOURCES AND WE CAN’T DO ANYTHING ABOUT IT • This natural radiation comes from cosmic rays, rocks and soil, food, human body & radon.

  31. Effects of Radiation Stochastic (Random effects) • Probability of an effect depends upon total dose received • Severity of effect is independent of the dose • Assumed there is no threshold (i.e. there is no dose below which effects do not occur) • Examples are cancer and genetic defects

  32. Cancer risksIt is assumed that any dose of radiation could potentially cause cancer.The bigger the dose, the more likely the effect will occur, (but it will probably never occur). i.e. a bit like crossing the road - the more times you cross the more likely you are to be run over, but probably never will. 37

  33. Effects of Radiation Deterministic Effects (Certain) Effects are certain to occur if sufficient radiation dose is received Severity will depend upon the dose received There are threshold doses for deterministic effects Skin ‘burn’ (or erythema) is 3 to 5 Gy Common in radiotherapy and occasionally in interventional procedures Examples are radiation sickness, erythema, infertility, cataract.

  34. Example of Radiation Injury in Cardiology • 40 year old male • coronary angiography • coronary angioplasty • second angiography procedure due to complications • coronary artery by-pass graft • all on 29 March 1990

  35. Fig. A 6-8 weeks after multiple coronary angiography and angioplasty procedures

  36. Fig. B 16 to 21 weeks after procedure, with small ulcerated area present

  37. Fig. C 18-21 months after procedure, evidencing tissue necrosis

  38. Fig. D Close up of lession in Fig. C From injury, dose probably in excess of 20 Gy.

  39. Fig. E Appearance after skin grafting procedure.

  40. Hair loss from CT scan • 53-year-old woman with subarachnoid hemorrhage • 4 CT perfusion scans and two angiographies of the head performed within first 15 days of admission • Bandage-shaped hair loss seen 37 days after first CT and lasted lasted for 51 days • (Imanishi et al 2005)

  41. Threshold risksOccur at Very large doses onlyThe bigger the dose, the more severe the effect Staff doses never this big

  42. How to Reduce Exposure to Scattered Radiation – Principles of Radiation Protection Management There are three principles of radiation protection: • Justification • All exposures to ionising radiations must be clinically justified – benefit must outweigh detriment • Optimisation • Once exposure has been justified it must be optimised i.e. lowest possible dose for acceptable image quality • Limitation • Radiation workers are subject dose limits by law

  43. Why is radiation potentially dangerous to workers such as yourself who are not irradiated by the X ray beam itself???????

  44. The real risk to staff

  45. Practical Means of Reducing Radiation Exposure • Time • Distance • Shielding