I. Introduction
? a lack of widely distributed recommendations to limit radiation exposure and its potential biological risks in cardiovascular practice
? few training programs and hospitals have well developed policies regarding radiation risk and exposure recommendations, particularly for pregnant women
? the ACC conducted a survey:  505 women respondents, 44% indicated they had altered their training or practice to reduce risk of radiation exposure, compared to 17% of 539 male respondents, only 19% referred to hospital or training program policies and 29% never obtained any information
? Many young practitioners, particularly women, select a specific area of cardiology that limits radiation exposure in training and practice, based on what is likely an inadequate knowledge of actual risk
? 1 Gray (Gy) = absorbed radiation dose of 1 J/Kg = 100 rads
? 1 sievert (Sv) = measure dose equivalent (radiation dose to tissue weighted by a factor related to the quality of the radiation) or effective dose equivalent (dose equivalent weighted by tissue weighting factors)

II. Personal Health Risks
? The biological effects of radiation depend on the amount of energy absorbed by the cells and where in the cell the energy is absorbed
? Deterministic effects include the following: erythema, desquamation, cataracts, decreased white blood count, organ atrophy, fibrosis and sterility. Onset depends on the absorbed dose, dose rate and the extent of the body area exposed. These effects have a dose threshold, and the intensity of the effect increases with increasing dose
? Stochastic effects include cancer and genetic risk. With stochastic effects, the probability of biological effect increases with increasing dose, but the intensity of the effect is not a function of the absorbed dose. E.g. a cancer produced by 100 rads is no worse than the same cancer induced by 10 rads

A.  Cancer
 
? Recent extrapolations based on observations from Hiroshima and Nagasaki indicate that the risk of fatal cancer due to whole-body X-ray exposure is approximately 0.04% per rem (4% per Sv) for levels encountered in medical settings
? recommended that safety Dose Equivalent to physicians and medical personnel averages less than 5 rem (50 mSv) per year as measured from a collar badge worn outside a lead apron. Since much of the body is shielded by the lead apron, a monitoring dosimeter worn outside lead shielding may overestimate the risk to the whole body by a factor of about 6. A Dose Equivalent of 5 rem (50 mSv) per year should be associated with a low incremental increase in risk (0.2% per year) compared to the lifetime risk of spontaneously occurring fatal cancer (estimated at 1 in 5 or 20% for the United States population)
? Assuming that the annual Dose Equivalent, measured by film badge, of a busy interventional cardiologist using a thyroid shield is 3 rem (30 mSv) per year, the cumulative occupational Dose Equivalent, measured outside a lead apron, would be in the range of 90 rem (900 mSv) over 30 years, which would be associated with a projected additional lifetime risk of developing cancer of about 3.6% [90 × 0.04%] in addition to the 20% estimated current risk of developing cancer in a lifetime. The estimated annual exposure for those who focus primarily on electrophysiologic procedures is lower, estimated to be less than 1 rem (10 mSv) per year, because of the reduced need for cineangiography and high intensity fluoroscopic imaging.
? Cardiologists' hands receive the highest X-ray exposure during catheterization and electrophysiologic procedures because the hands are closest to the X-ray beam
? hand exposures are frequently not monitored, Long-term "low" level radiation can pose a serious health risk, most cases occurred after years of radiation dermatitis and a long latent period
? Physicians performing fluoroscopy and cine angiography should take precautions to protect their hands. Leaded latex gloves provide only limited shielding capability, attenuating only 20% to 30% of the X-ray beam. Use of leaded gloves may be counterproductive if the gloved hands are directly imaged, since the automatic dose rate control on most equipment will increase the intensity to compensate for the radiopaque image in the field, thereby increasing the dose. Therefore, training is the key to reducing and maintaining low exposures to the hands. If an operator's hands are visible on the TV monitor or the cine film, then practices should be altered.
 
B. Cataracts

? Cataract formation is considered a deterministic effect of radiation exposure, i.e., its onset depends on the absorbed dose and rate of dose accumulation.
? Higher total doses can be tolerated when administered over longer time
? A cardiologist adhering to the recommended Dose Equivalent to the lens of less than 15 rem/year (150 mSv/year) may accumulate up to 423 rem (4.5 Sv) to the lens after working 30 years
? Although there are limited data defining the actual risk of cataracts for cardiologists and workers in cardiology laboratories, the risk for radiation-induced cataract formation is likely to be small
? Nonetheless, appropriate eye protection is warranted, leaded eyeglasses may reduce the risk of future cataract development.

C. Radiation-Related Risks Before Conception?enetic Risks

? The natural incidence of spontaneous genetic mutation is estimated to be 6% in humans, but there is still uncertainty about the quantitative additional effects of radiation
? projected that the risk of serious birth defects would be 8 × 10-5 to 1.2 × 10-4

 
D. Radiation Risks During Pregnancy

? Medical personnel may be concerned about their exposure to radiation if they are not appropriately protected during pregnancy because of the risks of fetal death, malformations, growth retardation, congenital defects, mental retardation and cancer induction
? The estimated radiation dose to an adult that could potentially cause temporary or permanent sterility in that adult is approximately 500 rads (5 Gy), embryonic death may occur at a dose of 10 to 50 rad (100 to 500 mGy). These doses are far in excess of the gonadal radiation exposure normally received by properly shielded radiation workers
? The maximum permitted dose for the fetus of a pregnant worker is 50 mrem (0.5 mSv) per month, or a total gestational Dose Equivalent of 500 mrem (5 mSv)
? In practice, if one assumes a fetal exposure equivalent of 3 mrem (0.030 mSv) per week measured under a 0.5-mm lead apron, the total gestational exposure would be about 120 mrem (1.2 mSv) for 40 weeks of gestation. The corresponding risk for in utero would be 1 in 4,166 (0.024)

III. Concepts of Protection

A. Principle of  "as Low as Reasonably Achievable" (ALARA)

? three cardinal principles of increasing distance, decreasing time and use of shielding in diverse settings and procedures

1.  X-Ray Intensity and Energy.
? Intensity refers to the number of X-ray photons in the X-ray beam, the greater the mA, the higher the X-ray intensity
?  penetrating ability of the beam is determined by the energy of the beam, which is controlled by voltage applied across the X-ray tube, a 15% increase in kV is equivalent to doubling the mAs
2.  Distance and Intensity.
? If the distance from the source is doubled, then the exposure is reduced to 1/4.
3.  Scatter X-Rays.
? When X-rays enter the patient, those that change direction and exit all sides of the patient, including back toward the X-ray tube, are scattered X-rays.
? factors affecting scatter levels are high kV and mA, wide open collimators and large distances between X-ray tube and image intensifier
 
The information in the table below reveals that physicians have the greatest radiation exposure in the cardiac catheterization laboratory and that nurses also receive considerable yearly exposure. Technologists and assistants receive considerably lower radiation exposure
 
 
 

C. Monitoring Personnel Exposures

1.  Dose Equivalent, Effective Dose Equivalent
? Dose Equivalent is the result of modification of the absorbed doses to reflect the fact that some types of radiation are more effective in producing biological effects than are others
? The Effective Dose Equivalent was introduced to allow for a consistent approach to estimating risks when different organs receive different levels of Dose Equivalent, it is used to assess the total risk of two specific radiation effects: risk of death from cancer and risk of severe hereditary effects for two
? The maximal allowable exposures for medical radiation workers from all sources are listed in the table below

2.  Film Badges.
 
? Personnel dosimetry monitors include those using X-ray film (film badges) or thermoluminescent dosimeters (TLDs), which use lithium fluoride crystals.
? Both detectors are placed in holders containing different filters. This allows the dosimetry laboratory to identify the type and energy of the radiation
? Monitors are typically worn for one month before being submitted for processing. The laboratory processing the film badges compares the density of the film in the badge worn by an individual exposed to an unknown amount of radiation to film densities from known exposures
? The solid lithium fluoride crystal atoms in a TLD absorb X-rays and their electrons are raised to a higher energy state after exposure to ionizing radiation. When the crystals are later heated, the excited electrons return to their normal energy levels and emit light in the process. The amount of light emitted is proportional to the amount of radiation the crystal received
? TLDs can be calibrated to provide tissue equivalent doses
? A particular advantage of the TLD is that the response is largely independent of the X-ray energy. However, they are more costly than film badges.
? Film badges can be rechecked at a future date if a reading is ever questioned, whereas TLDs can be read only once
 ? In practice, if a single badge is worn it is usually placed outside the apron at collar level. This monitors exposure to head, lens of the eye and neck and is important to ensure that lens and thyroid dose equivalents are within recommended limits
? When two badges are worn (as recommended), one is worn outside the apron at the neck and one is worn under the apron at the waist. The second badge monitors the effectiveness of the lead apron
? During pregnancy the under-apron waist badge will monitor fetal exposures.
? A third useful badge is the ring badge, which is particularly important in the nuclear laboratory when working with radiopharmaceutical injections
? Since the hands are often the closest part of the body to the beam and subject to the highest exposure, particularly during angiography involving the pelvic and femoral vessels, individual angiographers should consider the feasibility of wearing a ring badge.
? The NCRP recommends that an occupational worker's cumulative Effective Dose Equivalent should not exceed that person's age multiplied by 10
 

3.   Response to Overexposure.
? when radiation badges or review of personal exposure history indicates that exposure exceeds recommended (or personally acceptable) limits, it is vital that critical reviews of equipment performance and laboratory and individual practices be conducted
? a possible temporary reduction in number of cases
? to merely remove a worker from the laboratory without determining causes of the increased exposure is punitive, encourages poor compliance with monitoring requirements and ultimately endangers all laboratory personnel and possibly patients.
? Documenting fluoroscopy time and cine time per case and per type of procedure can be valuable in assessing patterns that may be contributing to increases in radiation exposure.

IV. Radiation exposure in cardiovascular procedures

A. Radiation Exposure During Diagnostic and Interventional Cardiac Catheterization
? In one recent study, the hospital radiation badges that most commonly exceeded established limits were worn by personnel in the cardiology division
? A prospective study of radiation practices suggested that cardiologists were probably inconsistent in their use of badges and appropriate shielding
? The implications are that cardiologists are exposed to significant levels of radiation that could pose a health hazard if they do not abide by standard safety precautions.
? Most catheterization laboratories monitor collar-level radiation exposure (outside the lead apron), and many also monitor waist-level exposure under the apron
? The mean collar-level exposure per case for physicians who perform coronary angiography and PTCA has been reported to be 4 to 16 mrem (0.04 to 0.16 mSv)
? The use of suspended leaded acrylic shields was variable in these studies
? The significant impact of operator technique on the level of exposure can be seen in the reduction of waist-level exposures (under the lead apron) from 3.3 mrem (0.033 mSv) to 1.4 mrem (0.014 mSv)/operator per week when operators restricted use of the LAO view (which results in much higher scatter at the cardiologist's position than the RAO view)
? In this study, LAO views resulted in 2.6 to 6.1 times the operator dose of equivalently angled RAO views.
? although cine generates far more radiation per second than fluoroscopy, the authors found that fluoroscopy was a greater source of total radiation by a ratio of 6.3 to 1 because of its protracted use
 ? waist-level exposure beneath a 0.5-mm lead apron was 1 to 2 mrem (0.01 to 0.02 mSv) per case for diagnostic coronary angiography and PTCA, representing approximately a 95% reduction in exposure from measurements outside the apron
? use of lead eyeglasses decreases radiation exposure to the lens to about 2.6 mrem (0.026 mSv) per case, representing a 35% reduction compared with measurements outside the
? other procedural modifications, including use of last image hold capability and pulsed fluoroscopy, should further reduce exposure.
? mean radiation doses of waist-level (under apron) and collar-level (outside apron) exposures during PTCA were 0.5 mrem (0.005 mSv) and 3 mrem (0.03 mSv) per case, respectively, for an assisting physician in one study (represent 10% to 30% of the primary operator's exposure)
? consistent with the observation that attending physicians generally have lower exposure levels than physicians-in-training who often spend more time in the position of the primary operator and work more slowly
? It should be recalled that the inverse square law is a potent factor influencing nonprimary operator and support staff exposure
? the exposure of a nurse stationed a few feet from the primary beam was 2% to 11% of the exposure for the primary operator, depending on the angulation of the beam relative to the nurse's position
 

B. Radiation Exposure During Electrophysiology Studies and Pacemaker Implantations

? scattered radiation during electrophysiology studies has been estimated using TLDs
? Appropriate collimation of the X-ray field reduced the exposure to the patient and to medical personnel by 40%.
? Exposure rates for the physician are considerably higher during manipulation of a catheter inserted through the subclavian vein because of closer proximity to the primary beam.
? The calculated Effective Dose Equivalent to the physician who manipulates catheters from the femoral area during an ablation procedure is 1.8 mrem (0.018 mSv) per case with an exposure of 55 minutes of fluoroscopy, which was the mean fluoroscopy time reported in one study
? The calculated Effective Dose Equivalent is 2.8 mrem (0.028 mSv) per case if a thyroid collar is not used
? A physician who performs 250 ablation procedures per year will incur a predicted Dose Equivalent of 423 mrem (4.5 mSv) per year, which is 9% of the recommended annual limit for radiation workers
? Despite the ongoing training of new fellows in clinical electrophysiology, there was a significant decrease in the amount of fluoroscopy used during ablation procedures
? While diagnostic electrophysiology studies and pacemaker implantations also require fluoroscopic guidance, these procedures generally employ only 5 to 10 minutes of fluoroscopy or less.
 V. Recommendations for Limiting Radiation Exposure
A. Fluoroscopy and Angiography in  Cardiac Laboratories

1.  Equipment Factors.
? Technical design changes available to reduce patient and operator dose during fluoroscopy include pulsed digital imaging, fluoroscopy, high efficiency image intensifiers, solid state coupling, thin copper filters, frame averaging and last image hold.
2.  Operator-Dependent Practices.
? Fluoroscopy should be used as sparingly as possible to position catheters, and pulsed digital fluoroscopy should be used when available
? Pulsed digital fluoroscopy maintains image quality while reducing exposures approximately 50% when compared to continuous fluoroscopy
? Since cine is a high dose imaging mode, it should be used efficiently for image recording
? Magnification should be used only when necessary as the dose is 1.7 times higher in the 7-inch mode compared to the 9-inch mode
? take advantage of the inverse square law, this effect is particularly dramatic for other medical personnel whose radiation exposure is low if they are properly positioned at distances greater than 8 feet from the patient.
3.  Shielding.
? Physicians should also make full use of personal shielding in using lead aprons, thyroid collars and leaded eye protection.
? Lead aprons and thyroid shields should be fluoroscoped at least annually to check for cracks and holes.
? Table side drapes and ceiling suspended leaded acrylic shields are important components of radiation protection. A leaded acrylic shield that is properly positioned can reduce exposure to the operator's thorax and head by about 90%

B. Recommendations for Radiation Protection in the Nuclear Laboratory

? The three cardinal principles of radiation protection :increase distance, decrease time, use shielding. (see table)
 

C. Recommendations for Radiation Protection of Women Staff Members Who Are or Desire to Become Pregnant

? the risk of genetic alteration of reproductive cells by radiation exposure is low
? It should be made clear that physicians may safely perform or assist studies during pregnancy, but ultimately, each woman has the prerogative to determine whether or not she will do so
? With planning, the cardiologist-in-training can meet procedural requirements even if she limits her radiation exposure during pregnancy.
? The NCRP recommendations state that the dose to the fetus from occupational exposure of a declared pregnant worker should not exceed 0.5 rem (5 mSv) over the entire pregnancy and 0.05 rem (0.5 mSv) during any single month of the pregnancy

Minimizing Radiation Exposure to the Pregnant Worker.
? In all laboratories, a second badge should be worn at the waist level under the lead apron to monitor fetal exposure. This "fetal" badge is worn in addition to the badge worn at the collar or chest level.
? Film badges should be monitored monthly. At present, some monitoring companies provide weekly reading for waist (fetal) badges so maternal exposure can be rapidly adjusted, if necessary
VI. Summary
? Given the large number of cardiac procedures involving radiation being performed in the United States by an increasing number of workers, the principles for reducing radiation and monitoring exposure should be known and followed by every practitioner, trainee and assistant in every laboratory
? The rapid development of new technologies in the cardiology laboratories and increasing volumes and case complexity all suggest that radiation protection is of vital and increasing importance.
? The health risks of radiation exposure and provided practice-specific recommendations for minimizing those risks.
? The concerns of women who are planning to become or who already are pregnant have been addressed.
? Future research will further modify procedures to reduce risks to the lowest possible level.
 

** END **