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Not all lightweight lead aprons and thyroid shields are alike

Open ArchivePublished:October 03, 2018DOI:https://doi.org/10.1016/j.jvs.2018.07.055

      Abstract

      Objective

      With the explosion of minimally invasive surgery, the use of fluoroscopy has significantly increased. Concurrently, there has been a demand for lighter weight aprons. The industry answered this call with the development of lightweight aprons. Our goal was to see whether lighter weight garments provide reduced protection.

      Methods

      Dry laboratory testing was performed in a standard X-ray room, using a standard fluoroscopy table and standard acrylic blocks. A commercial-grade pressurized ion chamber survey meter (Ludlum Model 9DP; Ludlum Measurements, Inc, Sweetwater, Tex) was used to detect gamma rays and X-rays above 25 keV. Nonlead aprons from several manufacturers were tested for scatter radiation penetration above the table at a fixed distance (3 feet) and compared with two standard 0.5-mm lead aprons of different manufacturers.

      Results

      Scatter measurements were made at 60 kVp and 70 kVp for pure lead (0.5 mm), mixed, and nonlead protective garments. Scatter penetration for the nonlead blends and barium aprons was 292% and 258%, respectively, at 60 kVp compared with the pure lead apron. At the higher beam quality of 70 kVp, the scatter penetration was 214% and 233% for the blend and barium aprons, respectively, compared with the pure lead apron. Our measurements demonstrate a noticeable difference in scatter reduction between pure lead and nonlead garments. Pure barium aprons and nonlead aprons from certain companies demonstrated scatter penetration that is inconsistent with the 0.5 mm of lead equivalence as claimed on the label. In addition, there was an incidental finding of a handful of lightweight aprons with significant tears along the seams, leaving large gaps in protection. Our study also demonstrates that several companies rate their lightweight garments as 0.5 mm lead equivalent, when actually only a small area on the chest and abdomen where the garment overlapped was 0.5 mm, leaving the rest of the garment with half the protection at 0.25 mm.

      Conclusions

      Our reliance on protective lead garments to shield us from the biologic effects of radiation exposure and the inferiority of some lightweight garments necessitate a streamlining of the testing methods and transparency in data reporting by manufacturers.

      Clinical Relevance

      However ergonomically efficient, some nonlead lightweight aprons do not offer the same radiation protection as standard 0.5-mm lead aprons. The authors suggest streamlining of testing methods and transparency in data reporting by the manufacturers of radiation protective garments so the end user has a clear understanding while making a purchase decision.

      Keywords

      Article Highlights
      • Type of Research: Experimental study of lead and nonlead protection garments
      • Key Findings: Some nonlead lightweight aprons did not offer the same radiation protection as standard 0.5-mm lead aprons.
      • Take Home Message: Radiation protection garments need standard measurements and accurate and transparent data reporting to allow easy understanding of their safety and efficacy data.
      With the explosion of minimally invasive surgery, the use of fluoroscopy has significantly increased over the years. At the same time, there has been a demand for lighter weight aprons because of an increased number of neck and back issues associated with wearing of heavier lead garments for long periods. The industry has answered this call with the development of aprons and thyroid shields made with lighter materials. Radiation protective clothing is a Food and Drug Administration class I device, a category with the least stringent requirement for classification.
      • Rees C.
      Views from an interventional suite: lightweight aprons exposed.
      Regulators reserve the right to audit manufacturers' claims, but manufacturers are essentially self-policing.
      • Jones A.K.
      • Wagner L.K.
      On the futility of measuring lead equivalence of protective garments.
      This has allowed companies to test nonlead garments using criteria meant to evaluate lead garments and thus falsely claim they are lead equivalent.
      • Rees C.
      Views from an interventional suite: lightweight aprons exposed.
      Although there are some nonlead garments that come close to the protection provided by lead, there are also nonlead garments that provide reduced protection, especially in the lower, more biologically harmful kilovoltage peaks, which make up the majority of scatter radiation to which staff is exposed.
      • Jones A.K.
      • Wagner L.K.
      On the futility of measuring lead equivalence of protective garments.
      • Christodoulou E.G.
      • Goodsitt M.M.
      • Larson S.C.
      • Darner K.L.
      • Satti J.
      • Chan H.P.
      Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter.

      Methods

      All testing was performed in a standard X-ray room, with a standard fluoroscopy table. Dry laboratory testing using standard acrylic blocks to simulate a patient was used. A commercial-grade pressurized ion chamber survey meter (Ludlum Model 9DP; Ludlum Measurements, Inc, Sweetwater, Tex) was used to detect gamma rays and X-rays above 25 keV (Model 9DP energy response: ±25% from 60 keV to 1.25 MeV). Nonlead aprons from several manufacturers were tested for scatter radiation penetration above the table at a fixed distance (3 feet) and compared with two standard 0.5-mm lead aprons of different manufacturers. Other than replacing different garments, all other factors in the experiment were held constant. Measurements were repeated three times to ensure reproducibility of the data. Pure lead aprons tested were 20 years old. All other aprons were <1 year old. Demographics included the C-arm (Philips Model BV 300; Philips Healthcare, Best, The Netherlands), average kilovolt potential and milliamperes during testing, and total above-table ambient scatter in milliroentgens on each side of the aprons. Because our measurements simulated a typical clinical setting, scatter measurement data likely have an insignificant contribution from stray radiation. However, results from the data follow the trend reported in previous studies.
      • Jones A.K.
      • Wagner L.K.
      On the futility of measuring lead equivalence of protective garments.

      Results

      Scatter measurements were made at 60 kVp and 70 kVp for pure lead (0.5 mm), mixed (containing some lead), nonlead blends, and pure barium protective garments. The lead-equivalent thickness was marked as 0.5 mm in the label for all the garments. Scatter penetration for the nonlead-containing blend and barium aprons was 292% and 258%, respectively, at 60 kVp compared with the pure lead aprons. At the higher beam quality of 70 kVp, the scatter penetration was 214% and 233% for the blend and barium aprons, respectively, compared with the pure lead apron (Table). Our measurements demonstrate a roughly 2:1 difference in scatter reduction between standard pure lead garments and the nonlead garments that we tested. Clinical relevance of this finding can be explained by considering, for example, a procedure with a reference air kerma of 2 Gy. Assuming that the operator's position is at 3 feet from the entrance skin, the scatter at the location is approximately 2 mGy. Using the penetration data for lead and nonlead garments from the Table, this results in an operator's exposure of 5 μGy and 20 μGy at 60 kVp and 10 μGy and 40 μGy at 70 kVp, respectively. Thus, there is a potential for an operator's exposure to be fourfold higher by using a nonlead garment. Pure barium aprons and the blend apron chosen for this study showed scatter penetration (Fig 1)
      • Eder H.
      • Panzer W.
      • Schöfer H.
      Is the lead-equivalent suited for rating protection properties of lead-free radiation protective clothing?.
      • Finnerty M.
      • Brennan P.C.
      Protective aprons in imaging departments: manufacturer stated lead equivalence values require validation.
      that is inconsistent with the 0.5 mm of lead equivalence radiation protection as claimed on the label. However, there was one company with a mixed apron (Mixed A; Burlington Medical, Newport News, Va) that had the same attenuation characteristics of the 0.5-mm pure lead apron. This same company's nonlead apron had a higher penetration but significantly less than that of their competitors. An incidental finding was that a handful of lightweight aprons had significant tears along the seams. This finding demonstrated large gaps in protection (Fig 2). We found a total of 30 different pieces of lightweight protective garments with significant tears of 300 tested. No such tears were found in pure lead aprons.
      TablePenetration of scattered radiation through different protective garments
      Lead typeScatterPenetration compared with pure lead
      At 60 kVp/1.5 mA, %At 70 kVp/2.6 mA, %At 60 kVp, %At 70 kVp, %
      Pure lead, 0.5 mm0.240.58
      Mixed A,0.5 mm0.230.47
      Nonlead A, 0.5 mm0.420.77
      Nonlead B, 0.5 mm0.941.82292214
      Pure barium, top0.861.93258233
      Pure barium, skirt11.85317219
      Figure thumbnail gr1
      Fig 1Scatter penetration at 60 kVp and 70 kVp for various protective garments.
      Figure thumbnail gr2
      Fig 2Nonlead lightweight aprons demonstrating significant tears along the seams, an incidental finding of this study. The tear originates at the seams and rips through the fabric because of the sheer weight of the garment.

      Discussion

      The use of fluoroscopy has significantly increased over the years. Because of this growing demand, >50% of vascular procedures are now performed in operating rooms that lack above- and below-the-table shielding, which is standard in dedicated interventional and cardiology suites. In addition, as minimally invasive procedures become more common in orthopedics and neurosurgery, exposure times have increased significantly in nonshielded operating rooms. Without this additional shielding found in dedicated interventional suites, C-arm guidance relies solely on protective clothing to protect the user from ambient low-energy scatter radiation. It is this low-energy scatter that is the source of the majority of the staff's whole body dose.
      • Schmid E.
      • Panzer W.
      • Schlattl H.
      • Eder H.
      Emission of fluorescent x-radiation from non-lead based shielding materials of protective clothing: a radiobiological problem?.
      Concurrently, there has been a demand for lighter weight aprons because of an increased number of musculoskeletal issues associated with wearing of heavier lead garments for long periods. The industry has answered this call with the development of aprons and thyroid shields made with lighter materials. Radiation protective clothing is a Food and Drug Administration class I device, a category with the least stringent requirements for classification.
      • Rees C.
      Views from an interventional suite: lightweight aprons exposed.
      Regulators reserve the right to audit manufacturers' claims, but manufacturers are essentially self-policing.
      • Rees C.
      Views from an interventional suite: lightweight aprons exposed.
      • Schmid E.
      • Panzer W.
      • Schlattl H.
      • Eder H.
      Emission of fluorescent x-radiation from non-lead based shielding materials of protective clothing: a radiobiological problem?.
      This has allowed companies to test nonlead garments using criteria meant to evaluate pure lead garments and ultimately claiming that they are lead equivalent.
      • Rees C.
      Views from an interventional suite: lightweight aprons exposed.
      Although there are some nonlead garments that come close to the protection provided by lead, there are also nonlead garments that provide reduced protection, especially in the lower range kilovoltage peaks, which makes up the majority of scatter radiation to which staff is exposed.
      Medical devices: radiology devices: personnel protective shield.
      Lightweight protective garments often contain a mix of light metals with varying protection to different wavelengths of radiation. Manufacturers do not make a full disclosure of the exact proportions of each lightweight element in the apron because of proprietary reasons.
      • Jones A.K.
      • Wagner L.K.
      On the futility of measuring lead equivalence of protective garments.
      What makes lead so protective against radiation is its high atomic number (Z) and density. High density in lead is due to a combination of its high atomic mass and the relatively small size of its bond lengths and atomic radius. The high atomic number and density make lead a more favorable material for photoelectric absorption. Thus, scattered photons encountered in diagnostic X-ray imaging can be effectively absorbed using 0.5 mm of lead. Besides being a soft metal, lead is easily molded to various shapes to be used in protective garments. Because the average energy of clinically used X-ray spectra is below the K-shell binding energy for lead, the secondary fluorescence emission from photon absorption in lead is insignificant. However, materials such as tungsten, iron, aluminum, barium, and antimony used in lightweight aprons can be activated to produce secondary fluorescence radiation.
      • Jones A.K.
      • Wagner L.K.
      On the futility of measuring lead equivalence of protective garments.
      • Christodoulou E.G.
      • Goodsitt M.M.
      • Larson S.C.
      • Darner K.L.
      • Satti J.
      • Chan H.P.
      Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter.
      • Finnerty M.
      • Brennan P.C.
      Protective aprons in imaging departments: manufacturer stated lead equivalence values require validation.
      • Eder H.
      • Schlattl H.
      • Hoeschen C.
      X-ray protective clothing: does DIN 6857-1 allow an objective comparison between lead-free and lead-composite materials?.
      • Schlattl H.
      • Zankl M.
      • Eder H.
      • Hoeschen C.
      Shielding properties of lead-free protective clothing and their impact on radiation doses.
      • Pichler T.
      • Schöpf T.
      • Ennemoser O.
      Radiation protection clothing in X-ray diagnostics—comparison of attenuation equivalents in narrow beam and inverse broad-beam geometry.
      • McCaffrey J.P.
      • Mainegra-Hing E.
      • Shen H.
      Optimizing non-Pb radiation shielding materials using bilayers.
      • McCaffrey J.P.
      • Tessier F.
      • Shen H.
      Radiation shielding materials and radiation scatter effects for interventional radiology (IR) physicians.
      • Akber S.F.
      • Das I.J.
      • Kehwar T.S.
      Broad beam attenuation measurements in lead in kilovoltage X-ray beams.
      Because the probability for photoelectric absorption is proportional to Z4, the lower atomic number materials used in lightweight aprons lack the stopping power of lead. Thus, the photon attenuation of pure lead is superior to that of the lightweight material.
      • Pasciak A.S.
      • Jones A.K.
      • Wagner L.K.
      Application of the diagnostic radiological index of protection to protective garments.
      • Lichliter A.
      • Weir V.
      • Heithaus R.E.
      • Gipson S.
      • Syed A.
      • West J.
      • et al.
      Clinical evaluation of protective garments with respect to garment characteristics and manufacturer label information.
      Manufacturers often claim that their aprons are “certified to the exacting standards of [the various governing bodies (International Electrotechnical Commission, Association of Surgical Technologists, or German Institute for Standardization)], leading to the misperception that these organizations require certain results to be achieved in order to grant a ‘certification.’ In reality, the standards do not certify anything, they are simply guidelines for testers on how to test and report results.”
      • Rees C.
      Views from an interventional suite: lightweight aprons exposed.
      Moreover, the standards do not require any minimum standards to be achieved in protective barrier attenuation. Other criticisms of the Standard Test Method for Determining Attenuation Properties (ASTM designation F2547-06) are described: the energy range is not broad enough (should include lower and higher kilovoltage peaks); a direct beam is used, whereas operators are exposed to scatter of a different quality; and the use of narrow-beam geometry is permitted, which can grossly underestimate exposure.
      • Rees C.
      Views from an interventional suite: lightweight aprons exposed.
      • Eder H.
      • Schlattl H.
      • Hoeschen C.
      X-ray protective clothing: does DIN 6857-1 allow an objective comparison between lead-free and lead-composite materials?.
      Companies frequently perform narrow-beam (single-beam) testing, including only the higher kilovoltage peaks (120 and 150 kVp). The lighter nonlead metals have similar results to lead in these ranges (Table; Fig 1).
      • McCaffrey J.P.
      • Mainegra-Hing E.
      • Shen H.
      Optimizing non-Pb radiation shielding materials using bilayers.
      However, broad- or wide-beam testing should be mandatory, with transmission values at all beam qualities (30, 60, 90, 120, and 150 kVp) because lighter weight materials do poorly in the lower energies (below 80 kVp) that make up the majority of scatter to which the staff is exposed.
      • Jones A.K.
      • Wagner L.K.
      On the futility of measuring lead equivalence of protective garments.
      • Christodoulou E.G.
      • Goodsitt M.M.
      • Larson S.C.
      • Darner K.L.
      • Satti J.
      • Chan H.P.
      Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter.
      • Eder H.
      • Schlattl H.
      • Hoeschen C.
      X-ray protective clothing: does DIN 6857-1 allow an objective comparison between lead-free and lead-composite materials?.
      • Schlattl H.
      • Zankl M.
      • Eder H.
      • Hoeschen C.
      Shielding properties of lead-free protective clothing and their impact on radiation doses.
      • Pichler T.
      • Schöpf T.
      • Ennemoser O.
      Radiation protection clothing in X-ray diagnostics—comparison of attenuation equivalents in narrow beam and inverse broad-beam geometry.
      • Muir S.
      • McLeod R.
      • Dove R.
      Light-weight lead aprons—light on weight, protection or labelling accuracy?.
      A difference in attenuation from 99% to 94% may not seem significant, but it would mean that the user would receive six times as much transmitted radiation.
      In addition, lead equivalence protection values should not apply only to the overlap zones, unless the overlap zones are complete from neck to bottom and from the posterior axillary line on one side to the other for the largest person who might wear that size of apron. Our study demonstrates that several companies rate their lightweight garments as 0.5 mm lead equivalent, when actually only a small area on the chest and abdomen where the garment overlapped was 0.5 mm, leaving the rest of the garment with half of the protection at 0.25 mm2 (Fig 3).
      Figure thumbnail gr3
      Fig 3Although the label may claim 0.5-mm lead equivalence, the thickness applies only to the overlap region as demonstrated in this apron.
      Manufacturers often use the overlap aprons to meet the minimum lead equivalent protection of 0.5 mm. Except for a small frontal strip in the center of the chest and abdomen, most of the coverage is only half at 0.25 mm, which provides an exponential reduction in coverage.

      Conclusions

      Our reliance on protective lead garments to shield us from exposure to scatter radiation and thereby minimize risk of biologic effects from the exposure is well documented. With the advent of nonlead protective garments, manufacturers have been allowed to self-regulate. Selectively chosen guidelines out of specifications for testing pure lead garments are used to incorrectly certify nonlead garments as having the required lead equivalence (commonly 0.5 mm of lead). Although hospital radiation safety programs are required to check the aprons for integrity under fluoroscope at least once a year, seldom is a quantitative evaluation of the lead equivalence of the aprons performed. Thus, industry-reported data are relied on for lead equivalence information for protective garments. Our experience, like that of others,
      • Jones A.K.
      • Wagner L.K.
      On the futility of measuring lead equivalence of protective garments.
      shows that protection offered by nonlead garments may not be the same as that of pure lead garments (we found one exception) across the spectrum of photon energy encountered clinically. With the proliferation of nonlead garments in clinical practice, a streamlining of the testing methods and transparency in data reporting by the manufacturers are needed. This will enable the end user to have a clear understanding while making a purchase decision for protective garments. Furthermore, it will be worthwhile for interventionalists to assess the lead equivalence protection offered by the light aprons as well as their structural integrity before deployment for clinical use.

      Author contributions

      Conception and design: DF
      Analysis and interpretation: EF, RS
      Data collection: JP
      Writing the article: JP, RS
      Critical revision of the article: EF, DF
      Final approval of the article: EF, JP, RS, DF
      Statistical analysis: Not applicable
      Obtained funding: Not applicable
      Overall responsibility: DF

      References

        • Rees C.
        Views from an interventional suite: lightweight aprons exposed.
        (Available at:)
        • Jones A.K.
        • Wagner L.K.
        On the futility of measuring lead equivalence of protective garments.
        Med Phys. 2013; 40: 063902
        • Christodoulou E.G.
        • Goodsitt M.M.
        • Larson S.C.
        • Darner K.L.
        • Satti J.
        • Chan H.P.
        Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter.
        Med Phys. 2003; 30: 1033-1038
        • Eder H.
        • Panzer W.
        • Schöfer H.
        Is the lead-equivalent suited for rating protection properties of lead-free radiation protective clothing?.
        Rofo. 2005; 177: 399-404
        • Finnerty M.
        • Brennan P.C.
        Protective aprons in imaging departments: manufacturer stated lead equivalence values require validation.
        Eur Radiol. 2005; 15: 1477-1484
        • Schmid E.
        • Panzer W.
        • Schlattl H.
        • Eder H.
        Emission of fluorescent x-radiation from non-lead based shielding materials of protective clothing: a radiobiological problem?.
        J Radiol Prot. 2012; 32: N129-N139
      1. Medical devices: radiology devices: personnel protective shield.
        (Available at:)
        • Eder H.
        • Schlattl H.
        • Hoeschen C.
        X-ray protective clothing: does DIN 6857-1 allow an objective comparison between lead-free and lead-composite materials?.
        Rofo. 2010; 182: 422-428
        • Schlattl H.
        • Zankl M.
        • Eder H.
        • Hoeschen C.
        Shielding properties of lead-free protective clothing and their impact on radiation doses.
        Med Phys. 2007; 34: 4270-4280
        • Pichler T.
        • Schöpf T.
        • Ennemoser O.
        Radiation protection clothing in X-ray diagnostics—comparison of attenuation equivalents in narrow beam and inverse broad-beam geometry.
        Rofo. 2011; 183: 470-476
        • McCaffrey J.P.
        • Mainegra-Hing E.
        • Shen H.
        Optimizing non-Pb radiation shielding materials using bilayers.
        Med Phys. 2009; 36: 5586-5594
        • McCaffrey J.P.
        • Tessier F.
        • Shen H.
        Radiation shielding materials and radiation scatter effects for interventional radiology (IR) physicians.
        Med Phys. 2012; 39: 4537-4546
        • Akber S.F.
        • Das I.J.
        • Kehwar T.S.
        Broad beam attenuation measurements in lead in kilovoltage X-ray beams.
        Z Med Phys. 2008; 18: 197-202
        • Pasciak A.S.
        • Jones A.K.
        • Wagner L.K.
        Application of the diagnostic radiological index of protection to protective garments.
        Med Phys. 2015; 42: 653-662
        • Lichliter A.
        • Weir V.
        • Heithaus R.E.
        • Gipson S.
        • Syed A.
        • West J.
        • et al.
        Clinical evaluation of protective garments with respect to garment characteristics and manufacturer label information.
        J Vasc Interv Radiol. 2017; 28: 148-155
        • Muir S.
        • McLeod R.
        • Dove R.
        Light-weight lead aprons—light on weight, protection or labelling accuracy?.
        Australas Phys Eng Sci Med. 2005; 28: 128-130