Radiation and Catheterization Lab Safety
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Transcript of Radiation and Catheterization Lab Safety
Radiation and Catheterization Lab Safety
Joan E. Homan, M.D.Cardiology Fellow
Catheterization Lab SafetyObjectives
Definitions Basic science Safety
Radiation - Terms
Dose Exposure and exposure rate Absolute dose Dose equivalent
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
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
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.
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)
X-Ray Tube Assembly
transmitted radiation
High voltage lead
current
Scattered radiaion
anode
filtration
Absorbed radiation
electrons
Target (ie patient)
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
X-ray tube
circuitry
Video Recorder
TV Monitor
Patient
Video camera
Image intensifier
Collimators
Fluoroscopy Imaging System
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)
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
Radon
Medical
Internal
Terrestrial
ConsumerProducts
Cosmic
Other
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
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
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)
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)
Image Intensifier Magnification Modes
9 inch field 6.5 inch field
Same area
Output phosphor
Input Phosphor
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
Exposure factors
Prolonged or repeated cine runs Longer fluoroscopy times Higher frame rates
All increase radiation exposure to the patient
Patient Factors
Age Health of patient Skin site
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
Radiation Biology
Radiation Injury Damage and repair Somatic effects Effects on developing embryo and fetus
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
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
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
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
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
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
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
Skin Edema
May appear in a few hours or a few weeks
The higher the dose, the shorter the period for appearance
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
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
Type III Injury
Necrosis within a few weeks of the acute exposure
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
Radiation Safety and Protection
Personal protection Time Distance Shielding
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)
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
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
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
*Reynaud L. A 5-y follow-up of the radiation exposure to in-room personnel during cardiac catheterization. Health Physics 1992:62(1); 10-15.
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)*
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
The End
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