Radiation and Catheterization Lab Safety

1. Radiation and Catheterization Lab Safety Joan E. Homan, M.D. Cardiology Fellow

2. Catheterization Lab SafetyObjectives • Definitions • Basic science • Safety

3. Radiation - Terms • Dose • Exposure and exposure rate • Absolute dose • Dose equivalent

4. Radiation - Terms • Exposure – • the amount of ionizing radiation a person is exposed to • expressed as roentgens (R) • Can be directly measured and is expressed as R/minute or milli-R/hour

5. Radiation - Terms • Absorbed Dose – • The amount of energy deposited in tissue, (the amount of radiation needed to transfer a certain amount of energy (1 joule/kg)). • Expressed as gray (Gy) or rad (1 gray = 100 rad) • Absorbed dose varies with type of tissue: • i.e. bone = 5.0 ; soft tissue = 0.95

6. Radiation - Terms • Dose Equivalent • The absorbed dose multiplied a quality factor allowing for different tissue sensitivities • Expressed as sievert (Sv) or rem (1 sievert = 100 rem) • Used to account for different biological effects of radiation • Rad, rem and roentgen have approximate numerical equivalence in the x-ray energy range used in the cardiac catheterization lab.

7. Radiation • Production • Current is applied to a filament • Electrons are released and accelerated towards a target by a high-voltage electrical potential • X-rays are produced when: • Electrons collide and are completely stopped by the target (characteristic x-rays) • Electrons are rapidly decelerated after striking the target (braking x-rays)

8. X-Ray Tube Assembly transmitted radiation Absorbed radiation Target (ie patient) Scattered radiaion electrons filtration current anode High voltage lead

9. Image Acquisition • Fluoroscopy – type of x-ray examination used for dynamic imaging • Image intensifiers - amplify the brightness of the image to improve visibility • X-rays transmitted through patient, enter the input phosphor which emits light that is then converted to electrical energy • The electrical energy is amplified and converted back into light at the output phosphor • Output phosphor of the image intensifier is coupled to a television pickup tube which converts the light pattern into an electrical signal which forms the image on the monitor

10. circuitry TV Monitor Video camera Video Recorder Image intensifier Patient Collimators Fluoroscopy Imaging System X-ray tube

12. Cine Angiography • Light exiting the output phosphor is divided, diverting part of the beam to TV monitor and the rest to the cine camera lens – refocuses light onto cine film • Standard cameras use 35mm film at frame rates of 15-60frames/sec (15-30fps for angiography and 60fps for ventriculography)

13. Environmental Radiation Exposure (mrem/year) • Natural Background • Cosmic rays 30-70 • External terrestrial 10-100 • Internal 10-20 • Radon 200 • Medical sources • X-rays 39 • Radiopharmaceuticals 14 • Man-made Sources • Fallout 3 • Nuclear industry <1 • Consumer products 3-4 • Airline travel 0.6 • Total 360

14. Radiation Dose and Dynamics • Limit of 10 R/minute • Patient radiation dose dependent on several factors: • X-ray tube factors • Image intensifier factors • Distance factors • Patient factors

15. X-ray tube factors • Operator independent: • kVp – voltage across the x-ray tube, the energy that accelerates the electrons • Intensity of x-rays and image brightness directly related to the current passing through the filament • Increasing the kVp produces higher energy x-rays which have greater penetrating power for larger patients • Optimal setting for adults – 70-80kVp • Copper or aluminum filters placed between x-ray tube and patient to absorb low energy x-rays that are inadequate for imaging purposes

16. Image quality • Automatic brightness control –automatically adjusted to maintain brightness • Collimation • restrict the size of the x-ray field • Field Size and Magnification • Field size decreases with magnification, therefore, the local patient radiation dose must increase to compensate for the loss of brightness • Low magnification (9-11 inch) • Intermediate magnification(6-7 inch) • High magnification (4-5 inch)

17. Image intensifier factors • Skin exposure • 1-2R/min in 9 inch mode • 2-5R/min for smaller magnification modes • For 10 minutes of fluoroscopy, patient’s skin exposure is 10-50R (10-50rads)

18. Image Intensifier Magnification Modes Same area Output phosphor Input Phosphor 9 inch field 6.5 inch field

19. Distance • Skin radiation increases with decreasing distance • Table height (height of operator) affects patient dose • Standard is to maintain 18” between x-ray tube and patient • Image intensifier should be as close to patient as possible

20. Exposure factors • Prolonged or repeated cine runs • Longer fluoroscopy times • Higher frame rates All increase radiation exposure to the patient

21. Patient Factors • Age • Health of patient • Skin site

22. Recommended Dose Limits for Occupational Exposure to Ionizing Radiation • Effective Dose Limits - Occupational • Annual 5000 millirem • Cummulative 1000 millirem x age • Annual Dose Limits for Tissues – Occupational • Lens of eye 15,000 millirem • Skin, hands, feet 50,000 millirem • Embryo fetus, total 500 millirem • Embryo fetus, monthly 50 millirem • Annual Public Exposure – Nonoccupational • Annual effective dose 100-500 millirem • Lens of the eye 1500 millirem • Skin, hands, feet 5000 millirem

23. Radiation Biology • Radiation Injury • Damage and repair • Somatic effects • Effects on developing embryo and fetus

24. Damage and Repair • Injury produced by large amounts of energy transferred to individual molecules • Causes ejection of electrons • Initiates physical and chemical effects on tissues especially DNA • Failure of repair mechanism leads to: • Cell death or • Mutation

25. Radiation Damage and Repair • Effects to tissue depend on: • Amount of energy imparted • Location and extent of region of body exposed • Time interval over which energy is imparted

26. Radiation Biology • Deterministic effects – those in which the number of cells lost in an organ or tissue is so great that there is a loss of tissue function • IE skin erythema and ulceration • Stochastic effects– occur if an irradiated cell is modified rather than killed and then goes on to reproduce • Do not appear to have a threshold and the probability of the effect occurring is related to the radiation dose

27. Somatic Effects • Observed early (days to weeks) • Early effects develop in proliferating cell systems (most radiosensitive skin, ocular lens, testes, intestines, esophagus) OR • Observed late (months to years) • Carcinogenesis is the most important delayed somatic effect • Delayed effects often seen in nerves, muscles and other radioresistant tissues

28. Groups at Increased Risk • Five groups of patients known to have genetic or chromosomal defects and an increased sensitivity to various types of ionizing radiation: • Xeroderma pigmentosum • Ataxia-telangiectasia • Fanconi’s anemia • Bloom Syndrome • Cockayne’s syndrome

29. Direct Radiation Effects • Determined by dose • Bone marrow depression with whole body radiation > 500 rad • Skin erythema occurs if a single dose of 6 – 8 Gy (600-800 rad) is given, and it is not identified until 1-2 days after irradiation • The higher the irradiation dose, the more quickly the erythema may be identified

30. Skin Erythema • Characterized by a blue or mauve discoloration of the skin • Increases during the first week • Usually fades during the second week • May return 2-3 weeks after the initial insult and last for 20-30 days • Acute doses in excess of 8 Gy will produce exudative and erosive changes in the skin • Penetrating doses in excess of 20 Gy: there is usually a nonhealing ulceration

31. Skin Edema • May appear in a few hours or a few weeks • The higher the dose, the shorter the period for appearance

32. Skin Injury by Type • Type I injury – damage limited to the epidermis and dermis without much damage to the subcutaneous tissues • Initial erythema • A 3-wk latency period • A secondary erythema followed by • An exudative epidermatitis and recovery in 3-6 months

33. Skin Injury by Type • Type II Injury • A vascular endothelitis • At least 6-8 months post exposure the acute reactions are renewed with necrosis and ulceration usually requiring surgery • A result of damage below the basal layer of the epidermis

34. Type III Injury • Necrosis within a few weeks of the acute exposure

35. Radiation Safety and Protection • Lab specific • Constructed with 1.5mm of lead or equivalent shielding to protect individuals in the control room and adjacent areas

36. Radiation Safety and Protection • Personal protection • Time • Distance • Shielding

37. Radiation Safety and Protection • Time • Radiation dose is proportional to exposure duration • Distance • Radiation dose is inversely proportional to the square root of the distance from the patient (or staff)

38. Radiation Safety • Shielding • Lead is the most common material used • A lead apron with an equivalent of 0.5mm of lead in front panel is mandatory • Lead in the back panel provides additional protection • Thyroid shield (0.5mm equivalence) is recommended to shield the sternum, upper breast and thyroid gland

39. Radiation Safety • Shielding continued • Leaded eyeglasses with the side shields reduce the exposure to the eyes and may improve visual acuity • Recommended for staff with collar-badge doses approaching 15rem per year and for interventionalist’s in training

40. Radiation Safety • Shielding continued • Hands receive the highest radiation dose, but are relatively insensitive to radiation • Supplemental lead shielding to reduce exposure to scatter is available in the form of table mounted lead drapes, ceiling mounted lead acrylic shields and rolling lead acrylic shields

41. Personnel Dosimetry • Interventionalists commonly assigned 2 radiation badges • One on collar • Second underneath lead apron • Lead apron reduces the radiation dose at the waist to 10% of dose at collar at 75kVp. • Effective dose equivalent best estimated by averaging the 2 dosimeters • Mean dose equivalent per procedure 4 +/- 2 millirem, highest doses were delivered to physicians in training (5 rem per year)*

42. Radiation Safety • Women of child-bearing age should receive a pregnancy test prior to procedure • Current regulations restrict radiation dose to the embryo and fetus to 500millirem for the entire gestation and a monthly dose < 50 millirem • Pregnancy does not exclude working in the cardiac catheterization lab • Highest danger of fetal abnormalities is in the first trimester • Maturity lead aprons provide an additional 1mm of lead equivalence • Use of properly fitting wrap-around apron provides same protection to the fetus • Fetal radiation badge should be worn on the abdomen under the apron to record monthly fetal exposure

43. The End

44. Bibliography • Braunwald, et al. Heart Disease, A textbook of Cardiovascular Medicine, 6th Edition, WB Saunders Company, 2001. • Mettler,FA, Upton, AC. Medical Effects of Ionizing Radiation, 2nd Edition, WB Saunders Company, 1995. • Mettler, FA, Voelz, GL. Current Concepts: Major Radiation Exposure – What to Expect and How to Respond. NEJM 2002; 346(20):1554-1561. • Safian, RD; Freed, MS. The Manual of Interventional Cardiology, 3rd Edition, Physician’s Press, 2001. • Shapiro, J. Radiation Protection, A Guide for Scientists, Regulators and Physicians, 4th Edition, Harvard University Press, 2002 • Wilde, P; Pitcher, EM; Slack, K. Radiation hazards for the patient in cardiological procedures. Heart 2001; 85(2): 127-130