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