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Operator Shielding: How and Why
Operator Shielding: How and Why Beth A. Schueler, PhD Staff are exposed to potentially high levels of radiation exposure during interventional radiology procedures. Radiation protection shielding devices should be used to help maintain personnel exposures as low as reasonably achievable. Body protection tools include lead aprons, thyroid shields, radiation protection cabins, and floor- and tablemounted shields. Eye protection tools include leaded glasses, ceiling-mounted shields, and protective patient drapes. Hand protection tools include leaded surgical gloves and protective patient drapes. For the most part, these radiation protection tools provide substantial dose reduction for personnel, with several notable exceptions. Leaded glasses without lateral protection do not provide adequate protection to operators because they are typically exposed to scatter radiation from the side. Leaded surgical gloves are not useful for hand protection when hands are placed in the primary x-ray beam. Although other radiation protection tools are effective, they come with drawbacks, including staff physical discomfort and reduced procedure efficiency. As a result, further development of new protection devices is encouraged. Tech Vasc Interventional Rad 13:167-171 © 2010 Elsevier Inc. All rights reserved.
D
uring interventional radiology procedures involving visualization of catheters, guidewires, and other devices under x-ray image guidance, operators and other staff in the procedure room are exposed to ionizing radiation. Studies reporting measurements of staff radiation dose show that high levels are possible.1-3 Particular concern has been noted with regard to radiation dose to the lens of the eye,4 hands,5 and lower extremities6 of the operator. It is possible for personnel to reduce occupational radiation exposure with careful attention to their actions during a procedure. Those actions include knowledge of the sources of radiation exposure and methods that can be employed to decrease exposure levels. The objective of this article is to review how occupational radiation dose can be reduced, particularly using protective shielding devices.
Sources of Personnel Radiation Exposure During interventional radiology procedures, personnel should be aware of 3 different types of ionizing radiation exposure: the primary x-ray beam, scattered x-rays, and leakage x-rays. Occupational exposure to the primary x-ray beam
Department of Radiology, Mayo Clinic, Rochester, MN. Address reprint requests to Beth A. Schueler, PhD, Department of Radiology, 200 First Street SW, Mayo Clinic, Rochester, MN 55905. E-mail: [email protected] 1089-2516/10/$-see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1053/j.tvir.2010.03.005
may occur when the operator manipulates devices positioned within the imaging field of view. Dose rates in this region are in the range of 5-20 mGy/h at the surface where the x-ray beam exits the patient during fluoroscopy. Scattered x-rays are produced within the patient tissue when exposed to the primary x-ray beam. These x-rays travel in all directions originating from the patient. Scatter dose rates are typically 1-10 mGy/h at the operator’s position. The third source of radiation is leakage x-rays that are emitted from the x-ray tube in areas other than the primary beam port. Equipment regulations limit the maximum leakage level to 1 mGy/h at 1 m from the x-ray tube for maximum operating kVp and continuous mA.7 For typical fluoroscopy techniques, leakage radiation is generally in the range of 0.001-0.01 mGy/h at the operator’s position, several orders of magnitude lower than scatter dose rates. Note that all 3 types of radiation are only present while the x-ray switch or foot pedal is engaged. As soon as x-ray production is stopped, primary, scatter, and leakage radiation are no longer present. Scatter levels decrease in proportion to the inverse squared distance from the irradiated patient volume. Figure 1 shows a typical scatter isodose plot for a C-arm configuration with undertable x-ray tube. Note that radiation intensity is concentrated in the area below the procedure table at the operator’s legs. This distribution is caused by higher levels of scattered x-rays produced at the primary x-ray beam patient input port. Forward scattered x-rays from the first few centimeters of tissue depth are heavily attenuated by the rest of the patient tissue, resulting in higher radiation levels in the re167
168
Figure 1 Scatter radiation isodose plot for a C-arm fluoroscopy system with undertable x-ray tube and overtable image receptor. Adapted and reprinted with permission.8 (Color version of figure is available online.)
gion back toward the x-ray tube. If the x-ray tube is instead positioned overhead, the highest scatter radiation intensity will be directed toward the operator’s head and neck. Similarly, for a lateral projection, the highest radiation area will be adjacent to the x-ray tube (Fig. 2).
Radiation Protective Equipment Various types of protective devices have been developed to shield staff from radiation exposure during interventional radiology procedures. These devices include apparel, such as aprons, thyroid shields, eyewear, and gloves. Also, mobile shields can be mounted on the floor, ceiling, and procedure table or placed on the patient. In general, shields should be used whenever possible to keep personnel exposure as low as reasonably achievable without lengthening the procedure or compromising patient safety.
B.A. Schueler The shielding material in protective garments can develop cracks and holes over time that are not visible externally. To help prevent this, aprons should be stored on a hanger with a minimum of folds. Also, garments should be monitored annually with fluoroscopy to check for holes and reduced shielding integrity. Studies have documented an increase in orthopedic problems in interventional physicians that are believed to be related to long-term use of heavy radiation-protective garments.9 To reduce the weight and improve comfort of protective garments, several improvements have been introduced. For most commercially available protective aprons sold today, lead has been replaced with lightweight lead composite or lead-free materials. Aprons made from these materials, including barium, tungsten, tin, and antimony, provide the same attenuation as an equivalent thickness of lead at approximately 30% of the weight.10 Another improvement is the vest and kilt garment design, which allows a portion of the weight to be distributed to the wearer’s hips, instead of concentrated on the shoulders and upper back as is the case with a traditional single-piece apron. Furthermore, mobile radiation protection cabins have been developed that eliminate the need for the interventional physician to wear a protective garment. These devices are either floor-mounted on wheels11 or ceiling-mounted on a suspension that moves with the operator.12,13 Armholes are included for patient access and transparent leaded shields provide full head protection. Although the operator’s mobility and patient access are somewhat restricted, these devices can provide an alternative to lead aprons. Thyroid shields are typically an optional radiation protection tool. They are recommended for personnel who receive monthly collar radiation monitor readings over 4 mSv.14 Weight and inconvenience to the wearer are relatively minimal, so thyroid protection is commonly used by workers receiving lower exposure levels also. It should be noted that their use becomes less critical for personnel over 40 years of
Protective Garments All personnel in a procedure room during fluoroscopy must wear a protective garment unless they are positioned completely behind a radiation shield. Radiation protective apparel is available in thicknesses ranging from 0.25- to 1-mm lead-equivalent thickness. In most areas, regulations require a thickness of at least 0.5 mm lead-equivalent be used, which attenuates over 90% of scattered x-rays that strike it. Different designs are available, including aprons with front coverage only, aprons that wrap around the body, and two-piece garments with vest and kilt. If personnel may have their back to the patient during the procedure, a wrap-around or vest/ kilt garment should be worn. Whatever design is selected, it is important to ensure that the garment fits properly with adequate coverage at the neckline and armholes. Proper apron sizing is also critical if the design includes 2 layers that must be overlapped to meet the lead-equivalent thickness specification.
Figure 2 Scatter radiation isodose plot for a C-arm fluoroscopy system in a lateral projection. (Color version of figure is available online.)
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age since the risk of radiation-induced thyroid cancer is reduced significantly with age.15
Eye Protection Until recently, it has been generally accepted that radiationinduced cataracts do not form below a threshold lens dose level. This threshold provided the basis for the maximum permissible dose of 150 mSv per year for the lens.16 However, new data on the radiosensitivity of the eye indicate the threshold dose may be significantly lower or zero.17,18 Therefore, careful attention to radiation protection of the eye is warranted to minimize cataract risk. Studies of occupational exposure in interventional radiology have shown high lens doses are possible and lens injury has been reported.19 As a result, it is recommended that physicians routinely performing interventional fluoroscopy procedures use protective shielding to reduce radiation exposure to the eye from scatter. Commonly, that protective shielding is provided by leaded eyewear or ceiling-suspended shields. Most commercially available protective glasses contain lenses of 0.75-mm lead-equivalent thickness, which provide over 95% attenuation of incident x-rays. However, in actual practice, the eye also is exposed to backscatter radiation from the head and incident radiation from the side. Typically, personnel are positioned to view the display monitor during fluoroscopy, which places their head at an angle to the scattering volume. As a result, the operator’s eyes are exposed to radiation from the side, unless the protective glasses are designed to block side exposure. Without adequate lateral protection, the protection factor of leaded glasses is less than expected from the attenuation of the lead-equivalent thickness alone. Moore et al report that without side shields, leaded glasses reduce eye exposure by a factor of only 2-3.20 Protective eyewear can be heavy and uncomfortable to wear on a regular basis. Alternatively, eye protection can be achieved with a ceiling-suspended mobile barrier. These shields may be partially or fully transparent to allow visualization of the patient and include a contour or attenuating drape along the lower edge to position around the patient (Fig. 3). Since the shield can be positioned to block the scattering tissue, significant dose reduction is possible at the operator’s position. Clinical measurements during interventional cardiology procedures showed eye doses were reduced by a factor of 19 using a ceiling-suspended lead screen.21 These devices provide the advantage of full head and neck protection for the operator and reduced scatter to other staff located within the shadow of the barrier. However, their usefulness is limited for procedures requiring direct patient access near the imaging field.
Hand Protection The operator’s hands are another area of concern for radiation protection. Hand doses during interventional radiology procedures can be high, particularly for percutaneous procedures.22 Measurements have shown that for most interventional procedures, the tips of the middle and ring fingers receive higher doses than other areas of the hand.5 Moreover, cases of skin damage in physicians who routinely place their
Figure 3 Interventional radiology procedure configuration showing ceiling-mounted and table-mounted radiation protection shields in place. (Color version of figure is available online.)
hands into the primary beam have been reported.14,23 Sterile protective surgical gloves providing radiation attenuation levels in the range of 15%-30% are available, but studies have shown they provide minimal protection when hands are placed in the primary x-ray beam for several reasons. Forward and backscattered x-rays within the glove add to hand exposure.24 In addition, the presence of attenuating material within the fluoroscopy automatic brightness control region results in an increase in x-ray technique factors, exposing the hand to a higher dose rate. These 2 factors, coupled with the false sense of security that may result in increased time spent in the primary beam, more than cancels out any protection the gloves may provide. It is recommended that hands be kept out of the primary x-ray beam unless it is essential for the safety of the patient. Whenever possible, the operator should work on the exitbeam side of the patient with the beam collimated to the area of interest. Tools that allow the hands to be located at a distance from the exposure area, including forceps, needleholders, and tube extensions, should be considered, as long as they do not add significantly to exposure time.
Other Types of Shielding Every interventional suite should include 1 or more large mobile shields mounted on wheels (Fig. 4). They are available in 1.0- to 1.5-mm lead-equivalent thickness, which provides nearly complete protection from scatter in the shield’s shadow. When the screens are made fully or partially from transparent lead glass, personnel can remain behind the barriers while still being able to observe the patient and the procedure. This shielding is particularly useful for personnel that remain in the procedure room during high-dose digital image acquisition.
B.A. Schueler
170
new and innovative ideas need to be introduced and tested. Interventional physicians are encouraged to work to support and advance this effort.
References
Figure 4 Interventional radiology procedure configuration showing floor-mounted radiation protection shield. (Color version of figure is available online.)
As shown in Figure 1, the highest concentration of scatter radiation is located in the region near the patient entrance beam port, which is under the table for a standard frontal C-arm projection configuration. This results in exposure to the operator’s lower extremities, which can be more that 5 times the exposure level measured by a radiation monitor located at the operator’s collar. Measurements of operator leg doses have been found to be as high as 2.6 mSv per procedure when no radiation shielding is used.6 In addition, potential radiation effects in skin on the legs below the level of the protective apron have been reported.23 Use of a detachable lead drape suspended from the side of the patient table (Fig. 3) has been shown to be an effective method of reducing lower extremity dose.25 Generally, these types of drapes are not obstructive; however, there are situations where the lead drape cannot be used, including procedures that require the C-arm to be angled such that the lead drape obstructs the x-ray tube. Shielding draped on the surface of the patient directly adjacent to the exposed area has been found to significantly reduce dose to the operator’s hands and head. Drape options include covered lead sheets26,27 and disposable sterile drapes constructed of bismuth or tungsten antimony.28,29 Since the drapes are radio-opaque, they may need to be repositioned if the x-ray beam position or angle is changed during the procedure.
Conclusions Ideal protective devices block all radiation from personnel without impeding access to or communication with the patient or causing physical discomfort for staff. Unfortunately, current protective equipment falls short of that ideal in varying degrees, leaving personnel to make compromises between their own protection, comfort, and efficiency. Many radiation protection tools come with drawbacks, including heavy and uncomfortable garments and shields with limited usefulness. To improve protection of personnel, additional
1. Marx MV, Niklason L, Mauger EA: Occupational radiation exposure to interventional radiologists: A prospective study. J Vasc Interv Radiol 3:597-606, 1992 2. Marshall NW, Noble J, Faulkner K: Patient and staff dosimetry in neuroradiological procedures. Br J Radiol 68:495-501, 1995 3. Vano E, Gonzalez L, Guibelalde E, et al: Radiation exposure to medical staff in interventional and cardiac radiology. Br J Radiol 71:954-960, 1998 4. Vano E, Gonzalez L, Fernandez JM, et al: Eye lens exposure to radiation in interventional suites: Caution is warranted. Radiology 248:945-953, 2008 5. Whitby M, Martin CJ: A study of the distribution of dose across the hands of interventional radiologists and cardiologists. Br J Radiol 78: 219-229, 2005 6. Whitby M, Martin CJ: Radiation doses to the legs of radiologists performing interventional procedures: Are they a cause for concern? Br J Radiol 76:321-327, 2003 7. International Electrotechnical Commission: Medical Electrical Equipment—Part 1-3: General Requirements for Basic Safety and Essential Performance—Collateral Standard: Radiation Protection in Diagnostic X-Ray Equipment, IEC 60601-1-3. Geneva, International Electrotechnical Commission, 2008 8. Schueler BA, Vrieze TJ, Bjarnason H, et al: An investigation of operator exposure in interventional radiology. RadioGraphics 26:1533-1541, 2006 9. Klein LW, Miller DL, Balter S, et al: Occupational Health hazards in the interventional laboratory: Time for a safer environment. J Vasc Interv Radiol 20:147-152, 2009 10. Yaffe MJ, Mawdsley GE, Lilley M, et al: Composite materials for x-ray protection. Health Phys 60:661-664, 1991 11. Dragusin O, Weerasooriya R, Jais P, et al: Evaluation of a radiation protection cabin for invasive electrophysiological procedures. Eur Heart J 28:183-189, 2007 12. Savage C, Carlson L, Clements J, et al: Comparison of the zero gravity system to conventional lead apron for radiation protection of the interventionalist. J Vasc Interv Radiol 20:s53, 2009 13. Pelz DM: Low back pain, lead aprons, and the angiographer. AJNR Am J Neuroradiol 21:1364, 2000 14. Wagner LK, Archer BR: Minimizing Risks from Fluoroscopic X-Rays: Bioeffects, Instrumentation, and Examination (ed 4). The Woodlands, TX, Partners in Radiation Management, 2004 15. National Academy of Sciences/National Research Council: Health risks from exposure to low levels of ionizing radiation: Phase 2, BEIR. VII, Board on Radiation Effects Research. Washington, DC, National Academies Books, 2006 16. National Council on Radiation Protection and Measurements: Limitation of Exposure to Ionizing Radiation, NCRP: Report Number 116. Bethesda, MD, National Council on Radiation Protection and Measurements, 1993 17. Worgul BV, Kundiyev YI, Sergiyenko NM, et al: Cataracts among Chernobyl clean-up workers: Implications regarding permissible eye exposures. Radiat Res 167:233-243, 2007 18. Klein BE, Klein R, Linton KL, et al: Diagnostic x-ray exposure and lens opacities: The beaver Dam eye study. Am J Public Health 83:588-590, 1993 19. Vano E, Gonzalez L, Beneytez F, et al: Lens injuries induced by occupational exposure in non-optimized interventional radiology laboratories. Br J Radiol 71:728-733, 1998 20. Moore WE, Ferguson G, Rohrmann C: Physical factors determining the utility of radiation safety glasses. Med Phys 7:8-12, 1980 21. Maeder M, Brunner-La Rocca HP, Wolbwer T, et al: Impact of a lead glass screen on scatter radiation to eyes and hands in interventional cardiologists. Catheter Cardiovasc Interv 67:18-23, 2006
Operator shielding 22. Stavas JM, Smith TP, DeLong DM, et al: Radiation hand exposure during restoration of flow to the thrombosed dialysis access graft. J Vasc Interv Radiol 17:1611-1617, 2006 23. Balter S: Interventional Fluoroscopy: Physics, Technology, Safety. New York, NY, Wiley-Liss, 2001 24. Wagner LK, Mulhern OR: Radiation-attenuating surgical gloves: Effects of scatter and secondary electron production. Radiology 200:45-48, 1996 25. Shortt CP, Al-Hashimi H, Malone L, et al: Staff radiation doses to the lower extremities in interventional radiology. Cardiovasc Interv Radiol 30:1206-1209, 2007
171 26. Kruger R, Faciszewski T: Radiation dose reduction to medical staff during vertebroplasty: A review of techniques and methods to mitigate occupational dose. Spine 28:1608-1613, 2003 27. Luchs JS, Rosioreanu A, Gregorius D, et al: Radiation safety during spine interventions. J Vasc Interv Radiol 16:107-111, 2005 28. Dromi S, Wood BJ, Oberoi J, et al: Heavy metal pad shielding during fluoroscopic interventions. J Vasc Interv Radiol 17:1201-1206, 2006 29. King JN, Champlin AM, Kelsey CA, et al: Using a sterile disposable protective surgical drape for reduction of radiation exposure to interventionalists. AJR Am J Roentgenol 178:153-157, 2002
D
uring interventional radiology procedures involving visualization of catheters, guidewires, and other devices under x-ray image guidance, operators and other staff in the procedure room are exposed to ionizing radiation. Studies reporting measurements of staff radiation dose show that high levels are possible.1-3 Particular concern has been noted with regard to radiation dose to the lens of the eye,4 hands,5 and lower extremities6 of the operator. It is possible for personnel to reduce occupational radiation exposure with careful attention to their actions during a procedure. Those actions include knowledge of the sources of radiation exposure and methods that can be employed to decrease exposure levels. The objective of this article is to review how occupational radiation dose can be reduced, particularly using protective shielding devices.
Sources of Personnel Radiation Exposure During interventional radiology procedures, personnel should be aware of 3 different types of ionizing radiation exposure: the primary x-ray beam, scattered x-rays, and leakage x-rays. Occupational exposure to the primary x-ray beam
Department of Radiology, Mayo Clinic, Rochester, MN. Address reprint requests to Beth A. Schueler, PhD, Department of Radiology, 200 First Street SW, Mayo Clinic, Rochester, MN 55905. E-mail: [email protected] 1089-2516/10/$-see front matter © 2010 Elsevier Inc. All rights reserved. doi:10.1053/j.tvir.2010.03.005
may occur when the operator manipulates devices positioned within the imaging field of view. Dose rates in this region are in the range of 5-20 mGy/h at the surface where the x-ray beam exits the patient during fluoroscopy. Scattered x-rays are produced within the patient tissue when exposed to the primary x-ray beam. These x-rays travel in all directions originating from the patient. Scatter dose rates are typically 1-10 mGy/h at the operator’s position. The third source of radiation is leakage x-rays that are emitted from the x-ray tube in areas other than the primary beam port. Equipment regulations limit the maximum leakage level to 1 mGy/h at 1 m from the x-ray tube for maximum operating kVp and continuous mA.7 For typical fluoroscopy techniques, leakage radiation is generally in the range of 0.001-0.01 mGy/h at the operator’s position, several orders of magnitude lower than scatter dose rates. Note that all 3 types of radiation are only present while the x-ray switch or foot pedal is engaged. As soon as x-ray production is stopped, primary, scatter, and leakage radiation are no longer present. Scatter levels decrease in proportion to the inverse squared distance from the irradiated patient volume. Figure 1 shows a typical scatter isodose plot for a C-arm configuration with undertable x-ray tube. Note that radiation intensity is concentrated in the area below the procedure table at the operator’s legs. This distribution is caused by higher levels of scattered x-rays produced at the primary x-ray beam patient input port. Forward scattered x-rays from the first few centimeters of tissue depth are heavily attenuated by the rest of the patient tissue, resulting in higher radiation levels in the re167
168
Figure 1 Scatter radiation isodose plot for a C-arm fluoroscopy system with undertable x-ray tube and overtable image receptor. Adapted and reprinted with permission.8 (Color version of figure is available online.)
gion back toward the x-ray tube. If the x-ray tube is instead positioned overhead, the highest scatter radiation intensity will be directed toward the operator’s head and neck. Similarly, for a lateral projection, the highest radiation area will be adjacent to the x-ray tube (Fig. 2).
Radiation Protective Equipment Various types of protective devices have been developed to shield staff from radiation exposure during interventional radiology procedures. These devices include apparel, such as aprons, thyroid shields, eyewear, and gloves. Also, mobile shields can be mounted on the floor, ceiling, and procedure table or placed on the patient. In general, shields should be used whenever possible to keep personnel exposure as low as reasonably achievable without lengthening the procedure or compromising patient safety.
B.A. Schueler The shielding material in protective garments can develop cracks and holes over time that are not visible externally. To help prevent this, aprons should be stored on a hanger with a minimum of folds. Also, garments should be monitored annually with fluoroscopy to check for holes and reduced shielding integrity. Studies have documented an increase in orthopedic problems in interventional physicians that are believed to be related to long-term use of heavy radiation-protective garments.9 To reduce the weight and improve comfort of protective garments, several improvements have been introduced. For most commercially available protective aprons sold today, lead has been replaced with lightweight lead composite or lead-free materials. Aprons made from these materials, including barium, tungsten, tin, and antimony, provide the same attenuation as an equivalent thickness of lead at approximately 30% of the weight.10 Another improvement is the vest and kilt garment design, which allows a portion of the weight to be distributed to the wearer’s hips, instead of concentrated on the shoulders and upper back as is the case with a traditional single-piece apron. Furthermore, mobile radiation protection cabins have been developed that eliminate the need for the interventional physician to wear a protective garment. These devices are either floor-mounted on wheels11 or ceiling-mounted on a suspension that moves with the operator.12,13 Armholes are included for patient access and transparent leaded shields provide full head protection. Although the operator’s mobility and patient access are somewhat restricted, these devices can provide an alternative to lead aprons. Thyroid shields are typically an optional radiation protection tool. They are recommended for personnel who receive monthly collar radiation monitor readings over 4 mSv.14 Weight and inconvenience to the wearer are relatively minimal, so thyroid protection is commonly used by workers receiving lower exposure levels also. It should be noted that their use becomes less critical for personnel over 40 years of
Protective Garments All personnel in a procedure room during fluoroscopy must wear a protective garment unless they are positioned completely behind a radiation shield. Radiation protective apparel is available in thicknesses ranging from 0.25- to 1-mm lead-equivalent thickness. In most areas, regulations require a thickness of at least 0.5 mm lead-equivalent be used, which attenuates over 90% of scattered x-rays that strike it. Different designs are available, including aprons with front coverage only, aprons that wrap around the body, and two-piece garments with vest and kilt. If personnel may have their back to the patient during the procedure, a wrap-around or vest/ kilt garment should be worn. Whatever design is selected, it is important to ensure that the garment fits properly with adequate coverage at the neckline and armholes. Proper apron sizing is also critical if the design includes 2 layers that must be overlapped to meet the lead-equivalent thickness specification.
Figure 2 Scatter radiation isodose plot for a C-arm fluoroscopy system in a lateral projection. (Color version of figure is available online.)
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age since the risk of radiation-induced thyroid cancer is reduced significantly with age.15
Eye Protection Until recently, it has been generally accepted that radiationinduced cataracts do not form below a threshold lens dose level. This threshold provided the basis for the maximum permissible dose of 150 mSv per year for the lens.16 However, new data on the radiosensitivity of the eye indicate the threshold dose may be significantly lower or zero.17,18 Therefore, careful attention to radiation protection of the eye is warranted to minimize cataract risk. Studies of occupational exposure in interventional radiology have shown high lens doses are possible and lens injury has been reported.19 As a result, it is recommended that physicians routinely performing interventional fluoroscopy procedures use protective shielding to reduce radiation exposure to the eye from scatter. Commonly, that protective shielding is provided by leaded eyewear or ceiling-suspended shields. Most commercially available protective glasses contain lenses of 0.75-mm lead-equivalent thickness, which provide over 95% attenuation of incident x-rays. However, in actual practice, the eye also is exposed to backscatter radiation from the head and incident radiation from the side. Typically, personnel are positioned to view the display monitor during fluoroscopy, which places their head at an angle to the scattering volume. As a result, the operator’s eyes are exposed to radiation from the side, unless the protective glasses are designed to block side exposure. Without adequate lateral protection, the protection factor of leaded glasses is less than expected from the attenuation of the lead-equivalent thickness alone. Moore et al report that without side shields, leaded glasses reduce eye exposure by a factor of only 2-3.20 Protective eyewear can be heavy and uncomfortable to wear on a regular basis. Alternatively, eye protection can be achieved with a ceiling-suspended mobile barrier. These shields may be partially or fully transparent to allow visualization of the patient and include a contour or attenuating drape along the lower edge to position around the patient (Fig. 3). Since the shield can be positioned to block the scattering tissue, significant dose reduction is possible at the operator’s position. Clinical measurements during interventional cardiology procedures showed eye doses were reduced by a factor of 19 using a ceiling-suspended lead screen.21 These devices provide the advantage of full head and neck protection for the operator and reduced scatter to other staff located within the shadow of the barrier. However, their usefulness is limited for procedures requiring direct patient access near the imaging field.
Hand Protection The operator’s hands are another area of concern for radiation protection. Hand doses during interventional radiology procedures can be high, particularly for percutaneous procedures.22 Measurements have shown that for most interventional procedures, the tips of the middle and ring fingers receive higher doses than other areas of the hand.5 Moreover, cases of skin damage in physicians who routinely place their
Figure 3 Interventional radiology procedure configuration showing ceiling-mounted and table-mounted radiation protection shields in place. (Color version of figure is available online.)
hands into the primary beam have been reported.14,23 Sterile protective surgical gloves providing radiation attenuation levels in the range of 15%-30% are available, but studies have shown they provide minimal protection when hands are placed in the primary x-ray beam for several reasons. Forward and backscattered x-rays within the glove add to hand exposure.24 In addition, the presence of attenuating material within the fluoroscopy automatic brightness control region results in an increase in x-ray technique factors, exposing the hand to a higher dose rate. These 2 factors, coupled with the false sense of security that may result in increased time spent in the primary beam, more than cancels out any protection the gloves may provide. It is recommended that hands be kept out of the primary x-ray beam unless it is essential for the safety of the patient. Whenever possible, the operator should work on the exitbeam side of the patient with the beam collimated to the area of interest. Tools that allow the hands to be located at a distance from the exposure area, including forceps, needleholders, and tube extensions, should be considered, as long as they do not add significantly to exposure time.
Other Types of Shielding Every interventional suite should include 1 or more large mobile shields mounted on wheels (Fig. 4). They are available in 1.0- to 1.5-mm lead-equivalent thickness, which provides nearly complete protection from scatter in the shield’s shadow. When the screens are made fully or partially from transparent lead glass, personnel can remain behind the barriers while still being able to observe the patient and the procedure. This shielding is particularly useful for personnel that remain in the procedure room during high-dose digital image acquisition.
B.A. Schueler
170
new and innovative ideas need to be introduced and tested. Interventional physicians are encouraged to work to support and advance this effort.
References
Figure 4 Interventional radiology procedure configuration showing floor-mounted radiation protection shield. (Color version of figure is available online.)
As shown in Figure 1, the highest concentration of scatter radiation is located in the region near the patient entrance beam port, which is under the table for a standard frontal C-arm projection configuration. This results in exposure to the operator’s lower extremities, which can be more that 5 times the exposure level measured by a radiation monitor located at the operator’s collar. Measurements of operator leg doses have been found to be as high as 2.6 mSv per procedure when no radiation shielding is used.6 In addition, potential radiation effects in skin on the legs below the level of the protective apron have been reported.23 Use of a detachable lead drape suspended from the side of the patient table (Fig. 3) has been shown to be an effective method of reducing lower extremity dose.25 Generally, these types of drapes are not obstructive; however, there are situations where the lead drape cannot be used, including procedures that require the C-arm to be angled such that the lead drape obstructs the x-ray tube. Shielding draped on the surface of the patient directly adjacent to the exposed area has been found to significantly reduce dose to the operator’s hands and head. Drape options include covered lead sheets26,27 and disposable sterile drapes constructed of bismuth or tungsten antimony.28,29 Since the drapes are radio-opaque, they may need to be repositioned if the x-ray beam position or angle is changed during the procedure.
Conclusions Ideal protective devices block all radiation from personnel without impeding access to or communication with the patient or causing physical discomfort for staff. Unfortunately, current protective equipment falls short of that ideal in varying degrees, leaving personnel to make compromises between their own protection, comfort, and efficiency. Many radiation protection tools come with drawbacks, including heavy and uncomfortable garments and shields with limited usefulness. To improve protection of personnel, additional
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