Radiation and catheterization lab safety
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Radiation and Catheterization Lab Safety. Joan E. Homan, M.D. Cardiology Fellow . Catheterization Lab Safety Objectives. Definitions Basic science Safety. Radiation - Terms. Dose Exposure and exposure rate Absolute dose Dose equivalent. Radiation - Terms. Exposure –

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Radiation and catheterization lab safety l.jpg

Radiation and Catheterization Lab Safety

Joan E. Homan, M.D.

Cardiology Fellow


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Catheterization Lab SafetyObjectives

  • Definitions

  • Basic science

  • Safety


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Radiation - Terms

  • Dose

    • Exposure and exposure rate

    • Absolute dose

    • Dose equivalent


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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


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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


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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.


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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)


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X-Ray Tube Assembly

transmitted radiation

Absorbed radiation

Target (ie patient)

Scattered radiaion

electrons

filtration

current

anode

High voltage lead


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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


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circuitry

TV Monitor

Video camera

Video Recorder

Image intensifier

Patient

Collimators

Fluoroscopy Imaging System

X-ray tube


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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)


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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


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    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


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    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


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    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)


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    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)


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    Image Intensifier Magnification Modes

    Same area

    Output phosphor

    Input Phosphor

    9 inch field

    6.5 inch field


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    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


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    Exposure factors

    • Prolonged or repeated cine runs

    • Longer fluoroscopy times

    • Higher frame rates

      All increase radiation exposure to the patient


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    Patient Factors

    • Age

    • Health of patient

    • Skin site


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    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


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    Radiation Biology Ionizing Radiation

    • Radiation Injury

      • Damage and repair

      • Somatic effects

      • Effects on developing embryo and fetus


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    Damage and Repair Ionizing Radiation

    • 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


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    Radiation Damage and Repair Ionizing Radiation

    • Effects to tissue depend on:

      • Amount of energy imparted

      • Location and extent of region of body exposed

      • Time interval over which energy is imparted


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    Radiation Biology Ionizing Radiation

    • 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


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    Somatic Effects Ionizing Radiation

    • 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


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    Groups at Increased Risk Ionizing Radiation

    • 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


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    Direct Radiation Effects Ionizing Radiation

    • 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


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    Skin Erythema Ionizing Radiation

    • 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


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    Skin Edema Ionizing Radiation

    • May appear in a few hours or a few weeks

    • The higher the dose, the shorter the period for appearance


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    Skin Injury by Type Ionizing Radiation

    • 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


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    Skin Injury by Type Ionizing Radiation

    • 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


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    Type III Injury Ionizing Radiation

    • Necrosis within a few weeks of the acute exposure


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    Radiation Safety and Protection Ionizing Radiation

    • Lab specific

      • Constructed with 1.5mm of lead or equivalent shielding to protect individuals in the control room and adjacent areas


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    Radiation Safety and Protection Ionizing Radiation

    • Personal protection

      • Time

      • Distance

      • Shielding


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    Radiation Safety and Protection Ionizing Radiation

    • 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)


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    Radiation Safety Ionizing Radiation

    • 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


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    Radiation Safety Ionizing Radiation

    • 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


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    Radiation Safety Ionizing Radiation

    • 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


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    Personnel Dosimetry Ionizing Radiation

    • 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)*


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    Radiation Safety Ionizing Radiation

    • 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


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    The End Ionizing Radiation


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    Bibliography Ionizing Radiation

    • 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


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