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
11
(No Transcript)
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 lt1
• 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, patients 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
• Fanconis anemia
• Bloom Syndrome
• Cockaynes syndrome

29
Direct Radiation Effects

• Determined by dose
• Bone marrow depression with whole body radiation
  gt 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
  interventionalists 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 lt 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,
  Physicians 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