Fluoroscopy Radiation Safety Training Manual

 

The use of X-ray fluoroscopy has increased dramatically in recent years and is spreading beyond the radiology department. Advances in medical technology have resulted in the development of powerful X-ray machines for complex procedures that use fluoroscopy extensively.  The use of such equipment by personnel who have not received specialized training in the proper use of radiation creates the potential for excessive radiation exposure to personnel and patients. Inadequate training combined with increased radiation outputs, higher X-ray tube heat capacities, and real-time digital image acquisition and storage can produce radiation doses that induce serious skin damage on a patient.

 

Procedures Involving Extended Fluoroscopy Exposures

(FDA 1994)

Radiofrequency cardiac catheter ablation
                  Percutaneous transluminal angioplasty (PTCA, PTA)
Vascular embolization
Stent and filter placement
Thrombolytic and fibrinolytic procedures
Percutaneous transhepatic cholangiography
Endoscopic retrograde cholangiopancreatography (ERCP)
Transjugular intrahepatic portosystemic shunt (TIPS)
Percutaneous nephrostomy, biliary drainage, or stone removal

 

Numerous instances of serious injuries have been documented, and they have spurred efforts to make specialized training available for fluoroscopists.The Ohio Department of Health (ODH) has mandated that individuals involved in fluoroscopy must undergo at least two hours of training.Paragraph (G) of Rule 3701:1-66-07 states:

††††††††††† ďAll individuals operating fluoroscopic radiation-generating equipment, and individuals likely to receive an annual effective dose equivalent in excess of one mSv (100 mrem) from participating in fluoroscopic procedures, shall receive at least two hours of radiation protection training specific to fluoroscopy in addition to the training required by rule 3701:1-38-10 of the Administrative Code prior to performing or participating in fluoroscopic procedures. Additionally, each individual shall receive one hour of re-training whenever the individual receives in excess of thirty percent of the allowable occupational dose measured over one calendar year.Ē

The complete rule may be viewed on the ODH website at

 

††††††††††† http://www.odh.ohio.gov/rules/final/f3701-1-66.aspx

 

The risk of adverse radiation effects originating from a medically necessary procedure is almost always offset by the benefit received by the patient. However, in order to improve the benefit-risk tradeoff for these procedures, it is incumbent on the operator to explore the reasons behind radiation effects that have occurred and to seek means by which to avoid them or reduce their severity in future cases.

Case Western Reserve University (CASE) is committed to comply with all the regulations of the Ohio Department of Health. In keeping with these commitments, technicians who energize fluoroscopy devices at CASE are required to be familiar with the radiation physics and safety principles necessary for safe operation. 

This training manual, written at the level of a primer, is intended to provide users of fluoroscopic equipment one means of achieving compliance with the ODH rule. It covers some basic principles of radiation physics, biology, and radiation safety in order to provide an understanding of the optimal utilization of fluoroscopy, while minimizing exposures to the patient, operators, and their colleagues.

Completion of this On-Line training module fulfills the didactic requirements for fluoroscopy privileges at CASE.  Minimum competency is verified through the completion of the Quiz found at the end of this manual.

 

Subject Index 

1.      Radiation Physics.

2.      Fluoroscopy Concepts.

3.      Radiation Environment.

4.      Radiation Biology.

5.      Case Studies.

6.      Reducing Radiation Exposure.

7.      Radiation Standard.

8.      References

 

 

Acknowledgement:This manual was reproduced in whole with the kind permission of, Mr. Bruce Demeza, ARSO of University Hospitals, Cleveland OH, and was based on material provided by and reproduced in part with the kind permission of Mr. ScottSorenson of St. Lukeís Hospital, Kansas City, MO.

 

   

   

Contact Information

Department of Occupational and Environmental Safety

Service Building 1st Floor

Radiation Safety 216-368-2906

Radiation Safety Officer

Dr. David Sedwick


Call Yelena Neyman at 216-368-4601


Fluoroscopy Radiation Safety Training Manual

Chapter 1: Radiation Physics

X-ray Production

X-rays are produced when high velocity electrons interact with the atoms of any material of high atomic number, such as the tungsten target in an X-ray tube. An electrically heated filament within the X-ray tube generates the electrons, that are then accelerated toward the tungsten target by applying a high voltage to the target. The speed of the electrons can exceed half the speed of light when they strike the target.

Xprod.jpg (56782 bytes)

The quantity of electron flow, or electric current, in the X-ray tube is described in units of milliamperes (mA). The maximum kinetic energy of the accelerated electrons is defined in terms of kilovolts peak (kVp). Fluoroscopy is usually performed using an average current of 1 to 5 mA at a peak electrical potential of 75 to 125 kVp.

The rate of X-ray production is directly proportional to the electron flow. Higher mA values indicate more electrons are striking the tungsten target, thereby producing more X-rays. If X-rays are generated at a fixed kVp and for a finite time interval, then the total quantity of X-rays produced depends directly on the product of the mA and exposure time, and is typically described in terms of mAs (the "s" stands for seconds).

Increasing kVp attracts more electrons from the filament, and also increases the rate of X-ray production. However, this relationship is not directly proportional.

Changing X-ray tube current can make the image on a video screen (or other display device) more or less bright, but it wonít change the contrast.Changing the tube voltage does affect contrast (see next subsection).

Only a small fraction of the energy imparted by the decelerating electrons is converted into X-rays. The rest of the energy is transformed into heat that must be dissipated in order for the X-ray tube to continue working. If the tube becomes too hot, such as when large amounts of X-rays are produced in a short period of time, the generator may shut down temporarily until the excess heat has been adequately removed.

X-rays are generated in all directions. The lead housing surrounding the X-ray tube blocks them except for the ones directed towards a small opening. The emerging beam of useful radiation is shaped by additional lead vanes called collimators, which can be adjusted to provide different beam shapes (round, square) or sizes (large, small).

Immediately prior to the collimators, the beam passes through thin plates of aluminum or copper called filters.Their function is to absorb those portions of the beam that have the lowest energy and are the least penetrating, often called ďsoftĒ x-rays.Otherwise these x-rays would be absorbed in the patient and unnecessarily contribute to the patientís dose.Most fluoroscopes have about 3 mm of aluminum filtration, but newer ones may have up to 1.0 mm of copper.

There are three outcomes when X-rays traverse tissue. They are:

 

fates 3.jpg (21691 bytes)

  • Complete penetration; X-ray passes completely through tissue and into the image recording device.
  • Total absorption; X-ray energy is completely absorbed by the tissue. No imaging information results.
  • Partial absorption with scatter; Scattering involves a partial transfer of energy to tissue, with the resulting scattered X-ray having less energy and a different trajectory. Scattered radiation tends to degrade image quality and is the primary source of radiation exposure to operator and staff

 

The probability of radiation interaction is a function of tissue electron density, tissue thickness, and X-ray energy (kVp). Dense material like bone or contrast dye attenuates more X-rays from the beam than less dense material (muscle, fat, air). The differential rate of attenuation provides the contrast necessary to form an image.

Density Effects:   The number of X-rays reaching the recording media (film, TV monitor) directly affect the image's brightness. 

Assume 1,000 X-rays together strike soft tissue and bone. Of them, 900 X-rays are capable of penetrating the soft tissue (less dense), while only 400 penetrate the bone (more dense).   The contrast between bone and soft tissue (900/400 = 2.25) quantifies the brightness difference seen on the displayed image.

 

Contrast 2.jpg (35179 bytes)

 

As tissue thickness increases, the probability of X-ray interaction increases. Thicker body portions remove more X-rays from the useful beam than thinner portions. This effect must be compensated for while panning across variable tissue thickness to provide consistent information to the image-recording device. It can be achieved by a feature commonly called "Automatic Brightness Control".

Thickness Effects:  Out of the 1,000 X-rays incident, 800 X-rays can penetrate the thin tissue portion while only 300 X-rays are capable of penetrating the thick portion.   The contrast between these tissues (800/300=2.7) quantifies the brightness difference seen on the displayed image.

thick absorb.jpg (35271 bytes)

 Higher kVp X-rays are less likely to interact with tissue and are described as more "penetrating." Increasing kVp, thereby generating more penetrating radiation, reduces the relative image contrast (or visible difference) between tissues of different densities. However, there is less radiation dose to the patient since fewer X-rays are absorbed.  The following figure illustrates this effect.  The X-rays that do not reach the image recording device are either absorbed in the patient (and contribute to patient radiation dose) or are scattered throughout the exam room (to increase staff radiation dose)

                                                       ††††† tubevolt.jpg (26630 bytes)

 

The following figure illustrates the effect of patient thickness on X-ray penetration.   

 

                         patthick.jpg (22533 bytes)

 

For a typical procedure involving a 20-cm thick patient and an X-ray tube voltage of 80 kVp:

  • Only 1 percent of the X-rays incident on the patient reach the image-recording device to yield useful information.
  • 99 percent of the X-rays are either absorbed within the patient (and contribute to patient exposure) or are scattered throughout the examination room (and contribute to staff exposure).

 

Divergent Nature of Radiation

The primary beam X-rays travel in straight but divergent directions as they exit the X-ray machine. The spread of the X-rays increases with distance from the X-ray origin (at the x-ray tube target). Consequently, the number of X-rays traveling through a unit area decreases with increasing distance. Likewise, radiation exposure decreases with increasing distance since exposure is directly proportional to the number of X-rays interacting in a unit area.

The inverse square law describes the degree of radiation exposure reduction caused by divergence:

                                           

where XA is the radiation exposure rate at distance DA, and XB is the radiation exposure rate at distance DB. This relationship indicates that doubling the distance from a radiation source decreases radiation exposure four-fold. Conversely, halving the distance increases exposure 4 times.

 

ISL.jpg (19397 bytes)

Inverse-Square-Law

1-Meter Distance: 1,000 X-rays pass through a unit area.   The amount of X-rays per unit area is 1,000.

2-Meter Distance:  With increasing distance, the beam diverges to an area 4 times the original area.  The same 1,000 X-rays are evenly distributed over the new area (4 times the original).  Thus the amount of X-rays per unit area is 250 or 1/4 the original.  The resulting radiation exposure is 1/4 the original.

 

 Application of inverse square law principles can yield significant reductions in patient and operator radiation exposure.

Example 1:

An operator normally stands 1 meter away from the patient during cineangiography. The exposure rate at this point is 15 mrem/min and total cineangiography time is 2 min. How much is her exposure reduced if she stands 1.2 meters away?

Solution 1:

The original exposure was 30 mrem (15 mrem/min for 2 min). The new exposure would be:

A 31% percent reduction in radiation exposure is achieved in this example.

Measuring Radiation Exposure

There is a myriad of terms that quantify radiation.  This is often confusing even to those quite familiar with radiation physics.  Terms which the physician should be aware of include those that:

  • Measure X-ray machine radiation output;
  • Measure patient radiation exposure; and
  • Measure personal radiation risk

 

roentgen.jpg (8430 bytes)X-ray machine output is often expressed in terms of Entrance Skin Exposure (ESE) and is the amount of radiation delivered to the patient's skin at the X-ray beam's entrance point.  ESE may also be described as "table-top dose."  Many X-ray machine regulations focus on the ESE.  In honor of Wilhem Roentgen (discoverer of X-rays, pictured left), the units of ESE have conventionally been roentgens per minute (R/min).

Patient radiation exposure is described in terms of radiation absorbed dose.  This is the energy absorbed per unit mass of tissue, and has the unit rad. Immediate biological effects caused by radiation are related to the absorbed dose expressed in rads.

Occupational radiation exposure is described in terms of radiation dose equivalent.  The unit used is the rem.  Rems are a measure of biological risk; an increase in rems is regarded as an increase in the probability of latent health effects.   In fluoroscopy, the risk of long-term effects from 1 rad of absorbed dose is equivalent to 1 rem (i.e., 1 rad = 1 rem).

The above units (roentgen, rad, rem) are becoming obsolete, and are being replaced by the new SI (international system) units.Exposure in air or at the skin surface is described in terms of air kerma, the energy deposited in unit mass of air by the X-rays.Both air kerma and tissue dose are now measured in grays, which are related to the older unit by

100 rads=1 gray (Gy)=1 000 milligrays (mGy).

Occupational exposure is measured in sieverts, where

100 rems= 1 sievert (Sv)= 1 000 millisieverts (mSv)= 1 000 000 microsieverts (uSv).

 

   

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Fluoroscopy Radiation Safety Training Manual

Chapter 2: General Fluoroscopy Concepts

Fluoroscopy System Description

Fluoro System (2).JPG (21400 bytes)Fluoroscopy imaging systems consist of an X-ray tube which produces X-rays, and an image receptor which converts the incident X-ray energy into a visible image. The output of the receptor is then distributed to a closed-circuit video system ultimately producing a "live" image on a video monitor. The output can also be distributed to recording mechanisms that store single images, or a succession of images that enable one to later review, say, the passage of contrast media in blood vessels. 

The figure on the left shows in schematic form the basic components of a conventional fluoroscopy system with an image intensifier.Actual systems will vary in detail and take different shapes.The cine camera has been replaced in modern systems by devices that record all images on magnetic media.

 

            

State-of-the-art devices have a digital flat panel detector, one of which is illustrated above.  It converts the x-ray energy directly into signals that ultimately display an image on a monitor.  Recording images is now always on digital media.

 

 

     

               

The photo images depict a mobile fluoroscope, often referred to as a ďC-armĒ, its control panel, and various components.Activation of fluoroscopic x-rays is usually with a foot-switch, although a switch may be present at a control panel or even on a hand-held module.

Radiation exposure during fluoroscopy is directly proportional to the length of time the unit is activated by the switch. Unlike radiographic X-ray units that take snapshots, fluoroscopic units do not have an automatic timer to terminate the exposure after a predetermined length of time. Instead, depression of the foot switch determines the length of the exposure, which ceases only after the foot switch is released.

Fluoroscopy machines are equipped with a timer and an alarm that sounds at the end of 5 minutes. The alarm serves as a reminder of the elapsed time and can then be reset for another 5 minutes.  

 

Automatic Brightness Control

Fluoroscopy machines produce images with a detector that captures the radiation exiting the patient. The detector converts the x-ray signal to electronic signals that can display a bright image on a TV monitor. The fluoroscopic machine can be operated in either a manual mode or in an automatic brightness control (ABC) mode.

When manual mode is used, the radiation exposure rate is independent of the patient size, body part imaged and tissue type. However, the image quality and brightness are greatly affected (often adversely) by these factors when the operator "pans" across tissues with different thickness and composition. For this reason, fluoroscopic examinations are almost always performed using ABC.

ABC mode was developed to provide a consistent image quality during dynamic imaging, When using ABC, the detector output is constantly monitored. Machine factors are then adjusted automatically to bring the brightness to a constant, proper level. When there is inadequate brightness (or too much), the ABC increases (or decreases) the mA, kVp, or both, depending on the device manufacturer.

Both patient and operator factors influence the number of X-rays reaching the detector. If less radiation is received by the detector, the ABC compensates for the loss in brightness of the video image by generating more x-rays (which increases radiation exposure) and/or making them more penetrating (which reduces image contrast).

Imaging Modes

Normally the radiation output from a fluoroscopy machine is sufficient to provide video images for guiding procedures or observing dynamic functions. A typical exposure rate at the X-ray beam entrance into the patient (ESE, or Entrance Skin Exposure) is 2 R/min.

fluoro1.jpg (26676 bytes)

The Food and Drug Administration (FDA) regulates the construction of all fluoroscopy systems. For routine fluoroscopy applications, the FDA limits the maximum ESE or table-top output to 10 R/min. The Ohio Department of Health also limits the ESE to  10R/min for general fluoroscopy use. For C-arm fluoroscopes, where there is no fixed table, the limit applies to a point 30 cm from the detector.

On some machines an operator can deliberately choose a setting that will increase the output. The use of higher radiation rates or "boost" modes are useful in situations requiring high video image resolution. ESE of up to 20 R/min is permitted for short duration. Special operator reminders, such as audible alarms, are activated during "boost" modes.

All new fluoroscopic devices include a pulse mode of operation, in addition to a continuous one.In this mode, depressing the foot pedal induces electrons to flow in spurts through the x-ray tube, rather than steadily, so that x-rays are generated in pulses.Sometimes the pulse rate can be varied (such as 30, 15, 7.5 per second).Radiation exposure is reduced significantly at lower pulse rates.

Old-fashioned cineangiography used to involve exposing cinematic film to the output of an image intensifier (II), thereby providing a permanent record of the imaged sequence. The II output required to expose film was much higher than the level needed for video imaging. Therefore initial X-ray levels also had to be much higher. Consequently, dose rates during cine recording were usually 10 to 20 times higher than normal fluoroscopy (i.e., ESE of 90 R/min or greater).  

CINE split.jpg (22040 bytes)

In modern cineangiography, film has given way to digital recording on magnetic media.The newer modality permits a reduction in patient dose as well as in operator dose, when performed correctly.  Nevertheless, exposure time in cineangiography should still be minimized.

Field Size and Collimators

The maximum useful area of the X-ray beam, or field size, is machine specific. Most fluoroscopy systems allow the operator to reduce the field size through the use of lead shutters or collimators.

Irradiating larger field sizes increases the probability of scatter radiation production. A portion of the increased scatter will enter the detector, degrading the resulting video image. Prudent use of collimators can also improve image quality by blocking-out video "bright areas," such as lung regions, allowing better resolution of other tissues.

 

 

Benefits from using collimation

Limiting beam size by using the collimators provides benefits to both patient and image. 

  • Less tissue is subject to radiation exposure, reducing patient risk and also scatter production. 
  • Reducing scatter radiation improves image quality since scatter only contributes noise to the image.

Collbens.jpg (24001 bytes)

 

Collimator use also reduces the total volume of tissue irradiated. When irradiation of tissue with little diagnostic value is avoided, the subsequent benefit-risk ratio is improved 

Magnification Modes

Many fluoroscopy systems have one or several magnification modes. In image intensifier systems, magnification is achieved by narrowing the x-ray beam so that a smaller portion of the input screen is irradiated, but then electronically manipulating the II to display a final image of the same original size. The input radiation is decreased, resulting in lower image brightness. The ABC system, in turn, compensates for the lower image brightness by increasing radiation production at the source, and subsequently increasing the radiation exposure to patient and staff.

 

Under Normal mode, there is little magnification with the whole beam used to generate a bright image.

Under Mag 1 mode, a smaller beam area is projected to the same II output.  The resulting object size is larger, but the image is dimmer due to the less beam input. 

The ABC system senses the brightness loss and either boosts machine X-ray output, increases tube voltage, or a combination of both.

FOV.jpg (31040 bytes)

The actual increase in X-ray output will depend on the particular device and the extent of magnification, but it will typically be a factor in the range of 1.5 to 4.

In modern fluoroscopic systems equipped with digital flat panel detectors, switching to a magnification mode leads to a similar shrinking of the x-ray beam which falls on the detector.The detailed mechanism of what follows is different from that in an II, but the result is again to boost the X-ray output.However, the increase is usually less than encountered for an II.

 

 

Grids

                     

A grid is a flat plate designed to remove scattered rays, but transmit the ones that pass straight through the patient. The image is clearer and sharper when the grid is used, but because fewer X-rays reach the II, the Automatic Brightness Control mechanism raises the exposure rate to the patient.  In situations when a large air-gap exists between the patient and the image receptor, some of the scatter misses the receptor, and therefore the grid can be removed to permit lower patient exposures.  In the case of pediatric patients, small body size may cause very low scatter, and removing the grid is strongly recommended.

Removable grids are present in only some fluoroscopic systems, like those used for GI exams.  The grid is not physically removed; instead a push-button mechanism automatically moves it out of the way when so desired.

 

Last Image Hold

Newer fluoroscopy units are often equipped with a last-view freeze-frame feature and/or video recording. Use of these modes allows the operator to view a static image at leisure, avoiding continuous patient and staff radiation exposure caused by continuous fluoroscopy use.

 

      

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Fluoroscopy Radiation Safety Training Manual

Chapter 3: Fluoroscopy Radiation Environment

Patient Exposure Profile

The greatest single source of man-made radiation exposure to the average person in the United States comes from medical irradiation. Medical doses range from a few mrads for a chest X-ray to thousands of rad in the treatment of cancer. According to Report No. 160 of the National Council on Radiation Protection and Measurements, the average U.S. citizen gets an effective dose from medical radiation of about 300 mrem per year, out of a total of 620 mrem.  Its relation to all other sources is illustrated in the pie chart below. (NCRP 2008)

An old study indicated that this exposure level could be reduced by optimizing the use of fluoroscopy (NRCP 1993).Note the emphasis it placed on optimizing operator technique.

Optimizing Action

Audio output related to X-ray machine output

Optimization of Video Camera system

Required switching between High (Boost) and Normal modes

Optimizing Operator Technique

Potential Dose Reduction Factor

1.3


3


1.5


2 to 10

During normal mode fluoroscopy, the average patient ESE is approximately 2 R/min. Within the patient the radiation intensity falls off exponentially with increasing tissue depth due to attenuation and inverse-square-law effects. Only approximately 1% of the original radiation beam reaches the image receptor.

The ESE exposure rate can be as high as 20 R/min under certain conditions such as using a high dose rate or "boost" mode and if the patientís skin is close to the X-ray tube. During cineangiography, ESE may exceed 90 R/min.

 

Operator Exposure Profile

The majority of the radiation dose received by the operator (provided the primary beam is avoided) is due to scattered radiation from the patient. After interacting with the patient, radiation is scattered more or less uniformly in all directions.

 

The intensity of scatter decreases with increasing distance, due to inverse square law effects. Consequently, scatter radiation is highest near its source (X-ray beam entrance point on the patient). In routine undertable fluoroscopy, radiation is attenuated severely by the patient, and therefore radiation levels are lower above the table than below. This effect is preferable since protective equipment worn by the operator (lead aprons) protects the body regions receiving highest exposure (waist, thighs).

 

 

 

patscat.JPG (40719 bytes)

Vertical Dose Rate.jpg (28747 bytes)

 

Radiation levels increase with decreasing distance from the patient.  Highest scatter radiation levels are often where the operator stands.  Radiation levels are highest beneath the table (when X-ray tube is below the table) because the patient provides an effective beam stop.  Highest levels are directed at the operator's waist.

 

The scatter radiation profile tilts with the X-ray tube if the latter is moved away from the posterior-to-anterior (PA) projection. During oblique angle projections where the X-ray tube is tilted towards the operator (detector is tilted away from the operator), there is a slightly higher exposure to the operatorís head and eyes. Conversely, radiation exposure is decreased when the X-ray tube is tilted away from the operator (detector tilted towards the operator). When possible, the operator should work on the detector side of the table when oblique angles are being imaged.

Tilt Profile-1.jpg (21754 bytes)

Tilt Profile-2.jpg (21908 bytes)

 

Effect of rotating X-ray system.  Images taken with the detector away result in higher radiation exposure to the operator's eyes compared to images with the detector towards the operator.

In general, an operator positioned 3 feet from the X-ray beam entrance area will receive 0.1% of the patientís ESE. Staff members positioned further away receive much less exposure due to inverse square law effects. In almost all cases, the operator will receive the highest occupational radiation exposure during the fluoroscopic procedure.

   

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Fluoroscopy Radiation Safety Training Manual

Chapter 4: Radiobiology

Biological effects of radiation

The lethal dose (LD50) in humans from acute, whole body radiation exposure is approximately 450 rads (4.5 Gy). The energy absorbed by the tissue will raise its temperature by approximately 0.01oC, which in itself of no consequence. The severe biological response is due to the ionizing nature of X-ray radiation, involving removal of electrons from molecular structures.

Atoms ionized by radiation may change chemically, becoming free radicals. These free radicals can damage a cellís DNA. The DNA may also be altered directly by radiation. In either case if the DNA is damaged, several things can happen. The most likely is that the damage will be repaired before the end of the cellís cycle. If not, the cell will probably die. There is some chance that the cell will survive and behave differently because of the damaged DNA. For example, it may become malignant. Large radiation doses may kill many cells causing noticeable damage such as erythema or epilation. Low doses do not cause such significant changes but may produce a malignant change.

 

DNAdamage.jpg (38901 bytes)

Photomicrograph showing examples of radiation-induced chromosome damage in cancer cells following radiotherapy treatment (Bushong 1980). 

Abnormal formations are readily seen at high dose levels, but are also observed at the lower doses received by diagnostic patients and highly exposed workers.

 

 

Human population groups in which radiation effects have been observed

(Bushong 1980):

American Radiologists
Atom bomb survivors
Radiation-accident victims
Marshall Islanders (Atomic bomb fallout)
Residents of areas having high levels of environmental radiation
Uranium miners
Radium watch-dial painters
Radioiodine patients
Children treated for enlarged thymus
Ankylosing spondylitis patients
Thorotrast patients (contrast containing radioactive material)
Diagnostic irradiation in-utero
Volunteer convicts
Cyclotron workers

Radiation sensitivity

Radiosensitivity at a cellular level is at least partly a function of the cell cycle depicted schematically in the figure.The G1 period is an interphase period during which the cell prepares for DNA replication, S is when the DNA replicates, and during G2 the cell prepares for chromosome condensation and mitosis.M is when mitosis or cell division takes place.The cell is most radiosensitive during the M phase, and less so during G1 and G2.The S phase is when it is most radioresistant.

According to the Law of Bergonie-Tribondeau, radiosensitivity is highest in undifferentiated and actively proliferating cells, proportionate to the amount of mitotic and developmental activity that they must undergo. For example, bone marrow is much more sensitive to radiation than nerve cells, which have an extremely long cell cycle.  The following list provides a relative ranking of cellular radiosensitivity (Seibert 1996):

 cellsen.jpg (28889 bytes)

The total dose, dose rate, fractionation scheme, volume of irradiated tissue and inherent radiation sensitivity all affect a given organís response to radiation. Generally, a large total dose, high dose rate, small fractionation schedule (as encountered during fluoroscopy), and large irradiated volumes cause a greater degree of damage. Less biological damage occurs when the radiation dose is fractionated (delivered over several different events as opposed to all at once), as is the condition of most operator/staff exposures. Dose fractionation allows time for cellular repair.

Deterministic Effects

A large number of ionizing radiation effects occur at high doses. These deterministic effects seem to appear only above a threshold dose. While the threshold may vary from one person to another, it is about 200 rad. The severity of these effects increases with increasing dose above the threshold. These so-called deterministic effects are usually divided into tissue-specific local changes and whole body effects, which lead to acute radiation syndrome.

 

deter.jpg (23066 bytes)

 

 

Effect

Threshold (rad)

Hours of Fluoro On-Time, 5 R/min

Hours of Cine On-Time, 30 R/min

Time to onset of effect

Transient Erythema

200

0.7

0.1

24 hr

Epilation

300

1

0.2

3 wk

Erythema

600

2

0.3

10 day

Pericarditis

800

2.7

0.4

>10 wk

Dermal Necrosis

1800

6

1

>10 wk

Skin Cancer

None Known

N/A

N/A

> 5 yr.

Cataract induction is of special interest to fluoroscopy operators since the lens of eye often receives the most significant levels of radiation (provided lead aprons are used). Radiation is known to induce cataracts in humans from single doses of 200 rad. Higher exposures can be tolerated when accumulated over time. Cumulative exposures of up to 750 rads have resulted in no evidence of cataracts. Personnel exposed to the maximum legally permissible levels each year would accumulate only 450 rems over 30 years. As such, the risk for cataracts is likely to be small.

Stochastic Effects

Somatic effects induced by radiation may include carcinogenesis. Experimental data have been interpreted as suggesting a non-threshold linear response for the dose-effect relationship, at least for some cancers. Then equal increases of dose cause a corresponding equal increase in the incidence of the effects. Such effects are also known as stochastic or probabilistic phenomena.

 stochastic.jpg (27412 bytes)

The U.S. National Council of Radiation Protection and Measurements (NCRP 1987a) estimated that an exposure of 1 rem to 1 million persons would result in an increase in cancer deaths from 190,000 to 190,400; an increase of 0.2 percent. According to the Biological Effects of Ionizing Radiation Committee (NRC 1990), a 10 rem dose to one's whole body could result in a 0.4% increase in the chance of getting a cancer in one's lifetime. For under 10 rem doses, no statistically conclusion could be drawn.

Studies on patients who have undergone radiation therapy indicate that the incidence for secondary malignancy ranges from 6 to 13 percent.   According to Hall (1999), these malignancies are attributed to:

  • Continued exposure to carcinogens (e.g., continued tobacco abuse or sun exposure)
  • Genetic susceptibility (e.g., familial cancers)
  • Treatment-induced second malignancies

Studies with an adequate cohort size clearly indicate an excess of second cancers induced by radiotherapy.  Studies suggest that the risks are concentrated in younger patients, that the breast is especially sensitive to radiation and that excess cancers develop with a latency of 10 years or more (Hall 1999).

There is limited data on the risk estimates for patients exposed during diagnostic procedures. Cancer risk estimates from lower radiation exposures are difficult to determine because of the high incidence of malignancy in the general, unexposed population. The effects from even lower radiation exposures (such as those encountered occupationally) are extrapolated from observations made at fairly high doses (Upton 1999).  The validity of this extrapolation is constantly being re-evaluated. Current guidelines maintain that current risk estimates are the best available for the purpose of establishing acceptable radiation exposure limits.

Unlike deterministic effects, stochastic effects are assumed to be unaffected by dose fraction, even though lab studies have shown that there is some decrease with fractionation. If the assumption holds, then the total risk to an individual is continually increased with increasing radiation exposure. For radiological workers, small savings in radiation exposure realized by altering technique can result in significant reductions in personal risk when integrated over a working lifetime. If the BEIR Committee's conclusion (NRC 1990) can be extrapolated to low doses, the following table can be constructed:

 

Annual Dose (rem)

30 year total dose (rem)

Incremental Fatal Cancer Risk

0.5

15

0.6 %

1

30

1.2 %

2

60

2.4 %

5

150

6 %

 

Radiation exposure can cause chromosomal damage that may be "repaired" with an incorrect sequence and subsequently be passed on to the next generation (genetic effects). Radiation does not cause new types of mutations, but simply increases the incidence of certain mutations above their natural rate of occurrence. Controlled studies of genetic effects are only available from animal models. The 7 million mice, "Megamouse" project revealed the following conclusions (Lam 1992):

  • Different mutations differ significantly in the rate at which they are produced by a given dose.
  • There is a substantial dose rate effect with no threshold for mutation production.
  • The male was more radiosensitive than the female. The males carried most of the radiation induced genetic burden.
  • The genetic consequences of a radiation dose can be greatly reduced by extending the time interval between irradiation and conception. Six months to a year is recommended.
  • The amount of radiation required to double the natural and spontaneous mutation rate is between 20 to 200 rads.

However, it must be pointed out that these conclusions have been confounded by studies of Hiroshima victims, among whom no genetic effects have been observed.

Prenatal Effects

Animal studies have shown that the embryo and fetus are more sensitive to the effects of radiation than the adult. There are three general prenatal effects observed that are dependent upon the dose and stage of fetal development:

  • Lethality.
  • Congenital abnormalities at birth.
  • Delayed effects, not visible at birth, but manifested later in life.

 

A dose of 250 rads or more delivered to a human embryo before 2 to 3 weeks of gestation will likely result in prenatal death. Those infants, who survive to term, generally do not exhibit congenitalprenatal.jpg (21604 bytes) abnormalities.

Irradiation of the human fetus between 4 to 11 weeks of gestation may cause multiple severe abnormalities of many organs.

Irradiation during the 11th to 15th week of gestation may result in mental retardation and microcephaly. After the 20th week, the human fetus is more radioresistant, however, functional defects may be observed. In addition, a low incidence (one in 2000) of leukemia has been observed in individuals who received prenatal radiation.

Medically indicated procedures involving radiation are appropriate for pregnant women (Brent 1999).  However, such procedures should be avoided if alternate techniques are available or measures should be taken to minimize patient/fetal exposure.  Considering legal complications resulting from non-optimal prenatal radiation exposure, it is strongly suggested that physicians consult with a Board-Certified Radiologist before performing fluoroscopy on potentially pregnant patients

   

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Fluoroscopy Radiation Safety Training Manual

Chapter 5: Case Studies of Radiation Injury

Non-Symptomatic Skin Reactions

Patients may not be aware of skin changes that take place as a result of lengthy fluoroscopic procedures (Wagner 1999):

  • Physical examination one year following coronary angioplasty identified a 1 x 2.5 cm-depigmented area with telangiectasia on the patientís left shoulder. Total fluoroscopy time: 34 minutes.
  • One year after PTCA involving 66 minutes of fluoroscopy, a 10-cm diameter hyperpigmented area with telangiectasia was evident on the patientís right shoulder.

These skin changes were in areas not visible to the patients and were only identified upon physical examination.

Symptomatic Skin Reactions

The circumstances leading to symptomatic radiation induced changes are varied. Case reports are grouped according to common factors in order to identify the reasons for radiation-induced effects.

PA Fluoroscopy

The posteroanterior (PA) orientation of the fluoroscope, when properly configured with the image intensifier down close to the patient, is probably the least problematic with regard to ESE rate. However, extended fluoroscopy usage has resulted in reports of skin damage.  The following case study illustrates this effect (Shope 1995).  

CS 1.jpg (57854 bytes)On March 29, 1990, a 40-year-old male underwent coronary angiography, coronary angioplasty and a second angiography procedure (due to complications) followed by a coronary artery by-pass graft. Total fluoroscopy time estimated to be > 120 minutes.   The image shows the area of injury six to eight weeks following the procedures. The injury was described as "turning red about one month after the procedure and peeling a week later." In mid-May 1990, it had the appearance of a second-degree burn.

 

 

CS 2.jpg (47411 bytes)

Appearance of skin injury approximately 16 to 21 weeks following the procedures with small ulcerated area present.

 

 

 

CS 3.jpg (50136 bytes)CS 4.jpg (80060 bytes)Appearance of skin injury approximately 18 to 21 months following procedures, evidencing tissue necrosis (and close-up of injury area)

 

 

 

CS 5.jpg (64450 bytes)Appearance of patient's back following skin grafting procedure

 

Additional reported cases of radiation-induced injury (Wagner 1999):

  • Following a transjugular intrahepatic portosystemic shunt (TIPS) procedure involving 90 minutes of fluoroscopy, a discharged patient developed erythema and discoloration on his back. One year after the TIPS procedure an ulcer developed, which did not heal, and two years later it was 4-cm in size. A split thickness skin graft from the right buttock was performed.
  • Following a TIPS procedure lasting 6 hours and 30 minutes (no indication of total fluoroscopy time), a 16- x 18-cm hyperpigmented area developed on the patientís back and progressed over a period of several months into a central area with ulceration. After 14 months a split thickness skin graft was performed leaving a depressed scar at the surgical sight.

These case studies indicate that extensive use of fluoroscopy can induce severe skin damage, even under the most favorable geometries.

Steep Fluoroscopic Angles

When the fluoroscope is oriented at a lateral or an oblique angle, two factors combine to increase the patientís ESE rate. The first is that a thicker mass of body tissue must be penetrated. The second is that the skin of the patient is closer to the source because of the wider span of anatomy (Wagner 1999).

  • A PA oblique angle using a C-arm involved 57 minutes of fluoroscopy. Twenty-four hours later the patient reported a stabbing pain in his right thorax. Three days later an erythema developed which evolved into a superficial ulcer. At two and half months after the procedure the area was approximately 12-cm x 6.5-cm and described as a brownish pigmented area with telangiectasia, central infiltration and hyperkeratosis.
  • A PA oblique angle was employed during a catheter ablation procedure involving 190 minutes of fluoroscopy. A symptomatic discoloration was noted several days after the procedure on the patientís left upper back. In the next few weeks the area had become painful and was draining. At seven weeks the area was approximately 7- x14-cm in size and described as a rectangular erythema with ulcers. After treatment, there was a gradual lessening of tenderness with reepithelialization, leaving a mottled slightly depressed plaque.
  • A steep PA oblique angle through the right shoulder was employed involving 51 minutes of fluoroscopy. Fourteen days after the procedure, an erythema appeared on the right shoulder that progressed into moist superficial ulcer with poor healing. This degenerated into a deep muscular ulcer requiring a myocutaneous skin graft approximately 14 months after the procedure.

The temporal progressions of these effects are consistent with high levels of acute exposure to x-ray radiation. The temporal differences in the responses are due in part to the levels of radiation received, but are also likely due to variations in radiation sensitivity amongst the patients.

Steep angled views, especially in large patients, often require penetration of large masses of tissue and dense bone, creating situations in which x-ray output rates are driven near or at the maximum (10 R/min)

Multiple Procedures

Although intervals between procedures should permit the skin to recover, healing might not be complete. This may lower the tolerance of the skin for further procedures (Wagner 1999):

  • A patient underwent two PTCA procedures about one year apart. Skin changes appeared approximately three weeks after the second procedure. At seven weeks a cutaneous ulcer had developed over the right scapula and healed without grafting.
  • A patient underwent two unsuccessful cardiac ablations involving approximately 100 minutes of fluoroscopy in a lateral oblique orientation. Approximately 12 hours after the second attempt, an erythema developed in the right axilla. At one month the area was red and blistering. At two years the area was described as a 10 x 5cm atrophic indurated plaque with lineal edges, hyper- and hypopigmentation, and telangiectasia. The patient was described as having difficulty raising her right arm.
  • Three PTCAs were performed on the patient, the last two completed on the same day approximately 6 months after the first procedure. The total fluoroscopy time was approximately 51 minutes. Erythema was noted immediately after the last procedure. This progressed from a prolonged erythema with poor healing into a deep dermal necrosis. The patient underwent a successful split thickness skin graft two years after the last procedure.
  • Past treatment of pulmonary tuberculosis often resulted in many patients undergoing extensive exposure to fluoroscopy. These patients had a demonstrated high incidence of breast cancer.

Previous procedures can lower the skinís tolerance for future irradiation. Prior to commencing any lengthy fluoroscopic procedure, the patientís medical history should be reviewed. The skin of the patient should be examined to ascertain if any skin damage is apparent should the patient have a history of lengthy fluoroscopic examinations. Direct irradiation of damaged areas should be avoided when possible.

Positions of arms

Keeping arms out of the x-ray beam during some procedures can be a difficult objective. Careful attention must be given to providing the arms with a resting position that will not restrict circulation but will at the same time maintain the arms in an area that is outside the radiation field (Archer 2000). 

 

 

A middle-aged woman had a history of progressively worsening episodes of arrhythmia. A radiofrequency electrophysiological cardiac catheter ablation was scheduled to treat the condition. The procedure employed 20 min of beam-on time for each plane of a bi-plane fluoroscope. Prior to the procedure the separator cones were removed so that the fluoroscopic c-arms could be easily rotated around the patient.  The separator cone is a spacer attached to the tube housing designed to keep the patient at a reasonable distance from the x-ray source. This is done specifically to avoid the high skin-dose rates that can be encountered near the tube port.

 

CSE1.jpg (49393 bytes)The patientís arms were originally placed at the patientís side but the right arm later fell into a lower position directly in front of this x-ray tube. However, personnel were not aware of this change because sterile covers were draped over the patient. The right humerus was directly in the beam at the port.  Because the separator cones were removed, the arm was only about 20Ė30 cm from the focal spot. With the soft tissue and bone of the arm directly in the beam, the automatic brightness control drove the output to high levels at the surface of the arm. The cumulative dose probably exceeded 25 Gy.

CSE2.jpg (64825 bytes)

The patient was released from the hospital the day after the procedure. At the time there were no complaints regarding her arm and no indication of erythema. About three weeks after the procedure, a bright erythema was demonstrated.

 

CSE3.jpg (70242 bytes)

The condition worsened and at five months a large ulcer the size of the collimated x-ray port developed.

 

 

CSE4.jpg (48176 bytes)CSE5.jpg (46277 bytes)At eight months a debridement was performed and a surgical flap was put in place. (Images before and after surgical flap)

The separator cone ensures that a minimal distance between the X-ray source and the patient is maintained (inverse square law effects). For some X-ray machines, the separator cone is designed to be removable in order to provide more flexibility in positioning for some special surgical procedures (e.g., portable C-arms). There is a risk of very high dose rates to the skin surface when it is removed.

Skin sensitivity

Some patients may be hypersensitive to radiation due to pre-existing health conditions (Wagner 1999).

         Erythema developed after diagnostic angiography and liver biopsy. Skin necrosis requiring rib resection evolved in the same patient after a TIPS procedure. The wound remained open for five years before a successful cover was put in place. Investigation into the events revealed that the patient suffered from multiple problems, including SjÝgrenís syndrome and mixed connective tissue disease.

 

Injuries to personnel

The following are modern-day examples of how improper use of the fluoroscope can lead to injuries in personnel (Wagner 1999).

         Hands of physicians have incurred physiologic changes indicative of high cumulative doses of chronic low-dose-rate irradiation. Brown finger nails and epidermal degeneration are typical signs. These changes were the result of years of inserting hands into the x-ray field with the x-ray tube above the patient.

         Four cases of radiation-induced cataract have been reported in personnel from procedures utilizing the x-ray tube above the patient orientation.

Doses accumulated to hands and eyes from frequently using the fluoroscope with the tube above the patient can be extremely high. Only routine application of proper radiation management techniques will be effective at avoiding such high doses.

 

   

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Fluoroscopy Radiation Safety Training Manual

Chapter 6: Reducing Radiation Exposure

A number of techniques exist to reduce radiation exposure to the patient.Though they may sometimes result in some loss of image quality, they should be practiced to the extent that they do not compromise the x-ray procedure.Their added benefit is that they also reduce exposure from scattered radiation to others in the room.Some methods described below will reduce exposure only to the operator and staff.

Obtain Appropriate Training

Every fluoroscopic equipment comes with a set of operating instructions.  When new equipment is installed the manufacturer's representatives will provide training in how to use it.  Trainees can then impart the knowledge to others who follow them.

It is very important to obtain that training before ever conducting a clinical procedure.  The training must take place in the absence of any patient or human volunteer.

Reduce Use Time

Radiation exposure during fluoroscopy is directly proportional to the length of time the unit is activated by the foot switch. Reductions can be realized by:

  • Not exposing the patient while not viewing the TV image;
  • Pre-planning images. An example would be to ensure correct patient positioning before imaging to eliminate unnecessary "panning;"
  • Avoiding redundant views;
  • Operator awareness of the 5-minute time notifications.

Fluoroscopyís real-time imaging capabilities are invaluable for guiding procedures or observing dynamic functions. However, there is no advantage over conventional X-ray techniques when viewing static images. Use of Last-Image-Hold features, when available, allows static images to be viewed without continuously exposing patient and operator to radiation.

Human eye integration time or recognition time of a fluoroscopy image is approximately 0.2 seconds.  Therefore, short "looks" usually accomplish the same as a continuous exposure.  Prolonged observation will not improve the image brightness or resolution (Seibert 1996).

Increase Operator Distance

Distance.jpg (21130 bytes)

 

 

 

 

 

Example 1 in Chapter 1 illustrated the benefits obtained from a small increase in operator distance from the patient. Personal technique should be self-evaluated periodically to identify whether opportunities for increasing distance exist. Standing one step further away from the patient can cut the physician's exposure rate by a factor of 4 (AAPM 1998).

approach.jpg (13661 bytes) 

 

 

 

 

 

In percutaneous transluminal techniques, using the femoral approach rather than the brachial approach yields distance benefits to the operator.

Substantial increases in operator distance may be realized through remote fluoroscopy activation whenever automated contrast injectors are used.

 Many procedures require staff to intermittently interact with the patient near the fluoroscopy system. The operator can reduce staff exposure by delaying fluoroscopy until these activities are completed and/or by alerting these personnel when imaging; especially during high dose rate modes like cineangiography.

 

Co-located.jpg (40739 bytes)

Minimize air gap between II and patient

Care should be taken whenever image view angles are changed during the procedure (e.g, changing from an ANT to a steep LAO). The image receptor is often moved away from the patient while changing X-ray tube position. Large air gaps can result if the height of the table or image receptor remains unadjusted:

 

Example 2:

After changing views, a 10-cm air gap between II and patient is inadvertently left behind. What is the increase in radiation exposure to a 20-cm thick patient positioned with the table 30 cm away from the X-ray source, assuming the ABC compensates by increasing mA only.

Solution 2:

Assuming the air gap could have been eliminated by moving II closer, and that the brightness loss follows the inverse square law:

The brightness level with the air gap is only 69% of the zero air gap brightness. The ABC system compensates for brightness loss by producing 31% more X-rays. The exposure rate to the patient and staff is subsequently increased by 31%

 

Illustration of fluoroscopy of a pelvic phantom with the II at its highest position. The probe under the phantom measures the ESE to be 5.25 R/min.

The II has been moved to a slightly lower position. The probe now reads 4.55 R/min.

 

 

In the case of portable C-Arm systems, eliminating the air gap ensures that the table top is as far away as possible from the X-ray tube, minimizing radiation exposure to the patientís skin. Note that the separator cone should always be re-positioned before commencing fluoroscopy on portable C-arm systems, as depicted below on the image at right.

   

Reducing air gaps between patient and image receptor like an II also reduces image blur.  Blurring of the image is caused by geometric magnification caused by air gaps:

gapblur.jpg (25388 bytes)

Gaps between patient and II enhance geometric magnification.  The objects will appear larger with increasing gap size.  However, note that image edges are more fuzzy.  The degree of "fuzziness" will increase with increasing air gap.

 

Minimize Use of Magnification

Use of magnification modes significantly increases radiation exposure to patient, operator, and staff (See Chapter 2). Magnification modes should be employed only when the increased resolution of fine detail is necessary.

 

Minimize Use of Grid

The grid, located just in front of the detector, removes some of the x-rays scattered from within the patient, and sharpens the TV image.It also increases the radiation exposure to the patient by as much as a factor of 2.When scatter is not a serious problem, use of the grid should be avoided.Examples are fluoroscopic procedures on a pediatric patient, or when circumstances dictate a large air gap (about 10Ē or 25 cm) between a patient and the detector

Collimate Primary Beam

Collimating the primary beam to view only tissue regions of interest reduces unnecessary tissue exposure and improves the patientís overall benefit-to-risk ratio.   Optimal collimation also reduces image noise caused by scatter radiation originating from outside the region of interest (See Chapter 2).

Collimate.jpg (29033 bytes)

A good rule of thumb is that fluoroscopy images should display the edges of the collimators when are available for use.

Use Alternate Projections

Steeply angled oblique images (e.g., LAO 50 with 30 cranial tilt) are typically associated with increased radiation exposure since:

  • X-rays must pass through more tissue before reaching the detector. Automatic brightness control (ABC) compensates for X-ray loss caused by increased attenuation by generating more X-rays;
  • Steep oblique angles are typically associated with increased X-ray tube to detector distances. The ABC compensates for brightness loss due to inverse square law effects by generating more X-rays.
  • Oblique views may bring the X-ray tube closer to the operator side of the table, increasing radiation exposure from scatter.

projection.jpg (23783 bytes)

Operator exposure from different projections.   Projections with the X-ray tube neutral or tilted-away from the operator are highlighted blue, while those tilted towards the operator are in red.  Note decrease seen between the LAO 40 views.  The caudal tilt causes the tube to be more tilted away from the operator.

 

When possible, use alternate views (e.g., ANT, LAO with no tilt) when similar information can be obtained.  The physician can reduce personal exposure by re-locating himself when oblique views are taken.  For example, dose rates can be reduced by a factor of 5 when the physician stands on the image receptor side of the table (versus X-ray tube side) during a lateral projection (AAPM 1998).

 

Optimize X-ray Tube Voltage

Selection of an adequate kVp value will allow sufficient X-ray penetration while reducing the patientís dose rate. In general, the highest kVp should be used which is consistent with the degree of contrast required (high kVp decreases image contrast).

 

Use Radiation Shields

Use of radiation shielding is highly effective in intercepting and reducing exposure from scattered radiation. The operator can realize radiation exposure reductions of more than 90 percent through the correct use of any of the following shielding options. Shields are most effective when placed as near to the radiation scatter source as possible (i.e., close to patient).

Many fluoroscopy systems contain side-table drapes or similar types of lead shielding. Use of these items can significantly reduce operator exposures. Many operators have had little difficulty incorporating their use, even during procedures requiring multiple re-positioning of the system.

Ceiling-mounted lead acrylic face shields should be used whenever these units are available, especially during cardiac procedures. Correct positioning is obtained when the operator can view the patient, especially the beam entrance location, through the shield.


shields.jpg (45776 bytes)

 

 

 

 

 

Portable radiation shields can also be employed to reduce exposure. Situations where these can be used include shielding nearby personnel who remain stationary during the procedure.

lead apron.jpg (13972 bytes)Use Protective Equipment

 

Use of leaded garments substantially reduces radiation exposure by protecting specific body regions. Many fluoroscopy users would exceed regulatory limits if lead aprons were not worn. At Case, whenever fluoroscopes are operated the operator and all staff within the room (or within 2 meters if using a mobile C-arm) are required to wear lead aprons.

Lead aprons do not provide total protection from radiation. An approximate 90% reduction in radiation exposure is obtained from wearing a lead apron. It should be noted that this effectiveness is reduced when more penetrating radiation is employed (e.g., ABC response to thick patients). Two piece lead apron systems are recommended since they provide "wrap-around protection" and distribute weight more evenly on the user. So called "light" aprons should be scrutinized to ensure that adequate levels of shielding are provided.

leadeff.jpg (23692 bytes)

Note higher tube voltages sharply reduces shielding benefits of lead aprons.  Higher tube voltages will occur when imaging large patients or thick body portions.  Also note that light aprons (0.25 to 0.35 mm Pb) provide less protection compared to the recommended 0.5 mm thickness.

 

Thyroid shields provide similar levels of protection to the individualís neck region. Thyroid shield use is recommended for operators who use fluoroscopy extensively during their practice.

Optically clear lead glasses are available that can reduce the operator's eye exposure by 85-90% (Siebert 1996).  However, due to the relatively high threshold for cataract development, leaded glasses are recommended only for personnel with very high fluoroscopy work loads (e.g., busy Radiology and Cardiology Interventionists).   Glasses selected should be "wrap-around" in design to protect the eye lens from side angle exposures.  Leaded glasses also provide the additional benefit of providing splash protection.

Conventional leaded gloves provide similar protection to the userís hands. However, trade-offs associated with their use include loss in tactile feel and increased encumbrance. For these reasons, use of leaded gloves is left to the operatorís discretion. To minimize radiation exposure to the hands, the operator should:

  • Avoid placing his hands in the primary beam at all times;
  • Place hands only on top of the patient.  Hands should never be placed underneath the patient or table top during imaging;
  • Consider using leaded gloves if hand placement within the X-ray beam is necessary or positioned nearby for extended periods of time.
  • Consider use of the newer "radiation-resistant" latex gloves impregnated with lead or something similar. They block only a fraction of the radiation, but they are better than nothing.

   

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Fluoroscopy Radiation Safety Training Manual

Chapter 7: Radiation Standards

 

Medical Dose Limits

Medical radiation exposures are intended to provide direct benefit to the patient. When the exposure is justified and the use optimized, the dose is considered to be as low as is compatible with the medical purposes. As such, regulatory bodies have not defined dose limits for medical procedures.

 

chest x-ray.jpg (6963 bytes)

 

 

 

 

 

 

 

 

 

 

 

 

 

Occupational Dose Limits

The Ohio Department of Health (ODH) has established upper limits on the amount of radiation that occupationally exposed personnel can receive. The following table provides the dose limits currently in effect:

 

 

Part of Body

Annual Maximum Dose

Annual Maximum Dose SI Units

Total effective dose equivalent

5 rems

0.05 Sv

Any organ, except lens of eye

50 rems

0.5 Sv

Len of eye

15 rems

0.15 Sv

Skin, extremities

50 rems

0.5 Sv

Fetus of declared pregnant worker

0.5 rems

0.005 Sv

 

Total effective dose equivalent (TEDE) is the weighted sum of doses to all parts of the body, and is loosely equivalent to a "whole body dose". It best relates overall biological risk to ionizing radiation.

A "declared pregnant worker" is one who has submitted a written declaration of her pregnancy to her supervisor or director. If there is no written declaration, then the same limits will apply as for any other personnel.

Although regulatory limits have been defined in terms of rems and sieverts, personnel radiation exposure are usually reported in units of millirem (mrem). 1 rem is equal to 1,000 mrem.   The vast majority of exposure reports for Case read zero or near zero.

ALARA Philosophy

The average radiation dose to workers in the United States is about 210 mrem per year (NCRP 1993):.  The risk associated with this exposure is equivalent to the annual risk of accidental death in general industry.  Workers receiving higher levels of exposure (i.e., approaching regulatory limits) would be subject to significantly greater risk than those unexposed to radiation.  For this reason, regulatory dose limits should be viewed as the maximum tolerable levels. Since stochastic radiation effects, such as carcinogenesis, cannot be ruled out at low levels of exposure, it is prudent to minimize radiation exposure whenever possible. This concept leads to the As-Low-As-Reasonably-Achievable (ALARA) philosophy.

Simply stated, the ALARA philosophy requires that all reasonable measures to reduce radiation exposure be taken. During fluoroscopy, the operator must judge what is reasonable. Prolonging the examination time is reasonable only if valuable information can be obtained. 

University Hospital of Cleveland maintains an ALARA policy on radiation. In addition to the operator's judgment, there are efforts to optimize equipment, room design, and procedures to keep exposures low. All facets of the radiation safety program are periodically reviewed with the same goal in mind.

For personnel who wear radiation monitors, there are action levels for their exposures that are set far below regulatory limits.

 

Millirems per calendar quarter

 

Level I

Level II

Total effect dose equivalent

250

375

Any organ except lens of eye

2500

3750

Lens of eye

750

1125

Skin, extremities

2500

3750

If a person's monitor indicates a dose that exceeds one of the above levels, the RSO investigates the circumstances and reports to a safety committee. For a dose between Level I and Level II no immediate corrective action is required, unless deemed appropriate by the RSO. Exceeding Level II means corrective action is required when possible.

Radiation Monitoring

Dosimeter 2.jpg (15281 bytes)Unlike many workplace hazards, radiation is imperceptible to human senses. Therefore, monitoring of personnel exposed to radiation is performed using a radiation dosimeter or "badge." Monitoring documents the level of occupational exposure. It is also useful in identifying both equipment problems and opportunities for improving individual technique (ensuring ALARA).

The State of Ohio requires radiation monitoring for all personnel whose occupational radiation exposure is likely to exceed 500 millirems (5 millisieverts), i..e. 10% of the maximum allowed, in a year.  For some radiation-related activities, including fluoroscopy, personnel must be monitored unless proof exists that the threshold will not be exceeded.

 

  

Individuals engaged in fluoroscopy receive a dosimeter that must be worn at or near the collar. It is important that the dosimeter is placed outside of any protective equipment that is worn (lead aprons or thyroid shield). Readings at this position provide an estimate of radiation exposure to the eyes. The TEDE is calculated using an appropriate algorithm.

 

A few individuals may be assigned two badges. In that case, the two will have distinctive markings, indicating that one must be worn at collar level outside a lead apron, and the other on the chest or waist under the lead apron. Again, appropriate algorithms will determine the TEDE.

In order to provide an accurate estimate of personal risk, radiation badges are to be used at all times when working with radiation. It is also important to turn in the radiation badges on time. The accuracy of the readings depends on the timely processing of the dosimeter.

The Radiation Safety Officer (RSO) reviews dosimetry records when they are received from the dosimetry vendor. Any exposures exceeding the established ALARA levels are investigated to determine whether corrective action can eliminate or reduce exposures for all concerned. The circumstances surrounding most cases of excessive radiation exposures are often readily mitigated.

Radiation dosimetry reports are provided annually to those CASE personnel who must be monitored for radiation exposure.  In addition, monthly or quarterly dosimetry reports are mailed to each participating department. Individuals can request their personal records at any time, and written dose estimates will be provided by the RSO.

How To Read the Radiation Dosimetry Report

A personnel monitor (or badge) typically has several sensitive zones, which are scanned with special equipment by the dosimetry company.Results are expressed as dose estimates in the report.An explanation of the entries:

USE column: Shows the type of badge - whether worn at the collar, waist, finger, etc.ďASSIGNĒ, when it is included, indicates a value calculated from the badge reading (or both badge readings if two are worn), and is a better measure of true biological risk.One of two formulas (EDE 1 or EDE 2) is used for the calculation, depending on the type of badges.

RADIATION QUALITY column: Filled in only sometimes with a code to indicate how energetic the radiation was, or how deeply it could penetrate.

The next four sets of three columns each show dose equivalents for (1) the latest badge period, (2) the current calendar quarter, (3) the current calendar year, and (4) the total since the present badge service began for the wearer.Within each set are three entries:

DEEP: Estimated dose equivalent at 1 cm depth in tissue.

EYE: Estimated dose equivalent to the eye at a depth of 0.3 cm.

SHALLOW: Estimated dose equivalent at a depth of 0.007 cm.

All numbers shown are doses received by the wearer above that due to normal background radiation.Background is approximately 30 mrem per month, or 90 mrem per quarter.For comparison, other typical doses are 10 mrem to the lung per chest x-ray, 200 mrem to a breast per mammogram, or 3000 mrem per CT scan.

If SL or M appears, it means the dose was below 10 mrem, and therefore an insignificant value.

Fluoroscopy Radiation Safety Training Manual

QUIZ

 

 

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