X-ray machines do not produce internal radiation exposure like radioactive materials.  There are three basic protection methods for external sources of radiation: Minimizing exposure time, maximizing distance from the X-ray tube, and the utilization of shielding.

Minimizing Exposure Time: Reduce "Beam-on-time"

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

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

Fluoroscopy’s 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 (Seifert 1996).

Maximize Distance

A small increase in the operator's distance from the patient can significantly reduce the  operator's exposure.  Standing one step further away from the patient can cut the physician's exposure rate by a factor of 4 (AAPM 1998) (Figure 5-1). You should periodically self-evaluate you personal technique to identify whether opportunities to increase distance exist.

Figure 5-1: Benefit of Increasing Distance

Courtesy of Sorenson, 2000.

 

In percutaneous transluminal techniques, using the femoral approach rather than the brachial approach yields distance benefits to the operator (Figure 5-2).

Figure 5-2: Influence of Technique

Courtesy of Sorenson, 2000.

 

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 (Figure 5-3).

Figure 5-3: Benefit of Alerting Staff

Courtesy of Sorenson, 2000.



Room Lighting

Provisions should be made to eliminate extraneous light that can interfere with the fluoroscopic examination. Room lighting should be dim to enhance visualization of the image. Excessive light can decrease the ability of the eye to resolve detail. Measures taken to improve detail often involve increasing patient/staff exposure.

X-ray Tube Position

Fluoroscopy examinations have the smallest operator exposure when the X-ray tube is underneath the examination table (Figure 5-3). Whenever possible, the operator should avoid the X-ray tube side of the table when imaging oblique or lateral images.

Figure 5-3: Benefit of Under-Table Position

Courtesy of Sorenson, 2000.

Note: The benefit is exaggerated-some operator dose occurs on the I-I side.
I-I to Patient Air Gap

The operator must be aware of the  X-ray tube-to-patient distance. Positions closer can lead to extremely high patient exposures due to Inverse-Square-Law effects (case study). Minimizing the air gap between the I-I and the patient typically ensures that this distance is maintained. Use of the separator or spacer cone can prevent serious effects. The spacer 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. Spacer cones protect patients from extremely high local exposures by making it physically impossible to get too close to the X-ray source (inverse-square law effects). For some X-ray machines, the spacer cone is designed to be removable (Figure 5-3) 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. 

Figure 5-3: Removable Spacer Cone

Courtesy of Rauch, 2000

Reduce Air Gaps

Keeping the I-I as close to patient’s surface as possible significantly reduces patient and operator exposures (Figure 5-4). The I-I will intercept the primary beam earlier and allow less scatter to operator and staff. In addition, The Automatic Brightness Control (ABC) system would not need to compensate for the increased X-ray tube to I-I distance caused by the air gap. The presence of an air gap will always increase patient/operator radiation exposure and decrease image quality.

Figure 5-4: Benefit of Reducing the Air Gap (I-I  Close to Patient)

Courtesy of Sorenson, 2000.

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

I-I to Patient Distance Example:

After changing views, a 10-cm air gap between I-I and patient is inadvertently maintained. 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? 

Note: mA only adjustments on ABC systems are reasonably common.

Solution:

Assuming the air gap could have been eliminated by moving the I-I 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%.


Reducing air gaps between patient and I-I also reduces image blur. Blurring of the image is caused by geometric magnification caused by air gaps. Gaps between patient and I-I enhance geometric magnification. The objects will appear larger with increasing gap size. However, note that image edges are more fuzzy (Figure 5-4). The degree of "fuzziness" will increase with increasing air gap.

Figure 5-4: I-I distance and Image Blur

Courtesy of Sorenson, 2000.

Courtesy of Sorenson, 2000.
Minimize Use of Magnification

Use of magnification modes significantly increases radiation exposure to patient, operator, and staff (See Chapter 3). Magnification modes should be employed only when the increased resolution of fine detail is necessary.

Collimate the Primary Beam

Collimating the primary beam to view only tissue regions of interest reduces unnecessary tissue exposure and improves the patient’s overall benefit-to-risk ratio. Optimal collimation also reduces image noise caused by scatter radiation originating from outside the region of interest (See Chapter 3). A good rule of thumb is that fluoroscopy images should not be totally "round" when collimators are available for use, the collimator edges should always be visible in the image.

Use Alternate Projections

Continuous exposure of the patient with the same projection (point of X-ray beam entry) can cause very high skin dose to small areas.  Thus, if the point of X-ray beam (projection) entry can be changed, the skin may be spared from the harmful effects of radiation.  While this is an effective protection method, care must be exercised to utilize this method intelligently since longer beam paths through the patient can cause higher patient and worker dose.

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 I-I. 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 I-I distances. The ABC compensates for brightness loss caused by 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. 

Operator exposure from different projections.

When possible, use alternate views (e.g., ANT, LAO with no tilt) when similar information can be obtained (Figure 5-5). 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 I-I side of the table (versus X-ray tube side) during a lateral projection (AAPM 1998).

Figure 5-5: Physician Exposure for a variety of Projections

Courtesy of Sorenson, 2000.

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 the decrease seen between the LAO 40 views. The caudal tilt causes the tube to be more tilted away from the operator.

Optimizing X-ray Tube Voltage

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

Henry Ford Hospital has many resources available (e.g., Staff Radiologists, Medical Physicists) to assist the operator in optimizing the fluoroscopy image while minimizing patient exposure.

Use of Radiation Shields

Use of radiation shielding is highly effective in intercepting and reducing exposure from scattered radiation (Figure 5-6). 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.

Figure 5-6: Benefit of Hanging Shield

Courtesy of Sorenson, 2000.

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.

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.

Use of Personal Protective Equipment

Use of leaded garments substantially reduces radiation exposure by protecting specific body regions. Many fluoroscopy users would exceed regulatory limits should lead aprons not be worn. Operator and nearby staff (within 2 meters) are required to wear lead aprons whenever fluoroscopes are operated at Henry Ford Hospital.  Due to the poor material qualities of Leaded garments, proper storage is essential to protect against damage (Figure 5-6).  Whenever leaded apron are required, they must be supplied and paid for by your employer (Henry Ford Health System)

Figure 5-6: Properly Stored Leaded Garments

Courtesy of Sorenson, 2000.

Courtesy of Sorenson, 2000.

Lead aprons do not stop all the x-rays.  Typically at least a 80% reduction in radiation exposure is obtained by wearing a lead apron (Figure 5-7). It should be noted that the apron's effectiveness is reduced when more penetrating radiation is employed (e.g., the ABC boost's kVp for thick patients). Two piece lead apron systems are recommended for most users since they provide "wrap-around protection" and distribute weight more evenly on the user. Some aprons contain an internal frame that distributes some of the weight from the shoulders onto the hips much like a backpack frame. So called "light" aprons should be scrutinized to ensure that adequate levels of shielding are provided.  State of Michigan law requires the use of 0.5 mm lead equivalent aprons.

Figure 5-7:  Lead Apron Protection Efficiency

Courtesy of Sorenson, 2000.


Note that higher tube voltages sharply reduces the 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 individual’s neck region. Thyroid shield use is required 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% (Siefert 1996). However, due to the relatively high threshold for cataract development, leaded glasses are only recommended 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. Progressive style lenses for bifocal prescriptions are available from a limited number of manufacturers.

The latex leaded gloves provide extremely limited protection. Standard (0.5 mm lead equivalent) leaded gloves provide useful protection to the user’s hands.   However, trade-offs associated with use of 0.5 mm leaded gloves include loss in tactile feel, increased encumbrance and sterility. For these reasons, use of leaded gloves is left to the operator’s discretion. To minimize radiation exposure to the hands, the operator should:

1. Avoid placing his hands in the primary beam at all times;  
2. Place hands only on top of the patient. Hands should never be placed underneath the patient or table top during imaging; 
3. Consider using leaded gloves if hand placement within the X-ray beam is necessary or positioned nearby for extended periods of time.

Radiation Monitoring-Dosimeter Badges

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 is useful to identify both equipment problems and opportunities for improving individual technique (ensuring radiation doses are ALARA). Monitoring also documents the level of occupational exposure. 

The requirements for dosimetry has been determined by the Radiation Safety Committee for each work area.  These specify the types of dosimeters issued as well as the collection frequency.  

Some workers are issued a single whole body badge (black figure icon). This whole body dosimeter should be worn on the collar outside of any protective equipment worn (lead aprons). Readings from this position provide an estimate of the radiation exposure to the eyes. Dose estimates to the individual’s whole body are made using the appropriate algorithm. Other workers are issued multiple dosimeters.  These are designed to be worn as shown (Figure 5-8):

Figure 5-8:  Protective Devices

Lieto and Jackson, 2000.

Ring badge and Sterility

Infection Control has evaluated the use of ring badges in surgical arenas.  For open surgical theaters, ring badges are contraindicated.  Catheter procedures may be performed with ring badges. 

Dosimetry Practices 

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 with the corresponding control dosimeters.

Absent dosimeters are taken very seriously by the institution.  Reports of which individuals have failed to properly return dosimeters (who did not report the loss of the dosimeter to the RSO) are sent to: the Radiation Safety Committee; the Department chairs; the Hospital Medical Executive Committee; and the Board of the institution.  To avoid this negative attention, turn your dosimeter in on time and promptly report the loss of a dosimeter to the Radiation Safety Office.  A new dosimeter will be issued at no cost and your good name will be preserved. 

The Radiation Safety Officer (RSO) reviews dosimetry records on a monthly basis. Investigations of any exposure exceeding the established standards are performed 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 reports are provided annually to all monitored personnel employed or practicing at Henry Ford Hospital. In addition, monthly reporting of radiation exposure is available for highly exposed fluoroscopy users. Individuals can access their personal records at any time, and written dose estimates are provided upon request.

ALARA Philosophy

Regulatory dose limits should be viewed as the maximum tolerable levels. Since stochastic radiation effects, such as carcinogenesis, can not 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. Typically, the operator defines what is reasonable. The principles discussed in this manual are intended to assist the operator in evaluating what constitutes ALARA for his/her fluoroscopy usage.

The Henry Ford Hospital administration is committed to ensuring that radiation exposure to its medical staff and employees is kept ALARA. Full attainment of this goal is not possible without the co-operation of all medical users of radiation devices.

Summary of Fluoroscopy Safety

1. Keep beam ON-time to an absolute minimum!
2. Always use tight collimation!
3. Do not overuse the magnification mode.
4. Keep the image intensifier as close to the patient as possible, and the tube as far away from the patient as possible.  
5. Keep the kVp as high as possible considering the patient dose versus image quality. 
6. Keep tube current (mA) as low as possible. 
7. Minimize room lighting to optimize image viewing. 
8. Do not overuse the high dose rate. 
9. Personnel must wear protective aprons, use shielding, monitor doses and know how to position themselves and the machines for minimum dose. 
10. Change projections angle for long procedures to minimize local skin doses.
11. Remember that the X-ray output, patient dose, and area scatter levels increase for larger patients.