Featured Article: K Fetterly et al. Head and Neck Radiation Dose and Radiation Safety for Interventional Physicians. JACC Vol 10 No 5 2017.

This excellent study provides very sound confirmation of our own findings that attenuating head caps do very little to protect the brain due to their geometry relative to the scatter field. It also confirms older studies showing the poor lens protection provided by leaded glasses, especially to the contrateral (often the right) eye where it is nil. Head and neck protection requires large shields located between the patient and the operator’s head, and uncomfortable wearable gear is insufficient.

Full text is available here: http://interventions.onlinejacc.org/content/jint/10/5/520.full.pdf

Key excerpts:

LEAD GLASSES: “…Similar to the findings of Geber et al. (19), the results of this work indicate incomplete protection of the ocular lenses by the glasses. In particular, neither model of glasses protected the ocular lens contralateral to scatter source. This is because dose to the contralateral lens enters the eye obliquely through the face, whereas the glasses preferentially protect against radiation incident from the front.

ATTENUATING HEAD CAP:  “This work demonstrates that the radiation absorbing surgical cap provides essentially no protection to the brain of an interventional physician. This result is readily explained by geometry…This finding contradicts marketing materials and published works suggesting that these or similar types of caps offer substantial brain protection (13–15). The experimental methods used in these other works measured attenuation of the surgical cap rather than dose to tissues. As demonstrated herein, the optimistic perspective that radiopaque surgical caps substantially reduce brain dose is misleading.”

“The Effects of Attenuation Properties and Back Coverage of Protective Clothing and Devices on Operator Exposures in the Interventional Suite”

ABSTRACT: Many different personal radiation protection options are available today for use by interventionalists in their suites. This study examines a variety of options to determine the importance of lead vs. lead-free, back coverage vs. none, and frontal overlap vs. none. Secondary scatter was provided by a stack of acrylic (phantom patient) and exposure was measured for the phantom operator (a life-size frame “wearing” the personal protection) while standing in a typical position during fluoroscopy. The results show that operator exposure is mostly influenced by the attenuation properties of the protective material and that garments with open backs often protect better than wrap around styles due to lesser attenuation capacities of the material used in the latter, and because secondary scatter from other objects in the room is far lower than the frontal primary scatter from the patient even after penetration of the material. The results also raise concerns as cited in other reports about the attenuating power of styles which employ: 1. Labeled Pb-equivalency only in the overlap zones, leaving the sides with lower attenuation, 2. Lead-free varieties whose Pb-equivalency labels may not apply to the entire spectrum of scattered radiation in a clinical environment.

INTRODUCTION: This test of several personal protection garments and devices being used in an operational interventional suite was performed to examine the variability of their attenuations of the scattered radiation, as well as the impact, if any, of whether or not they cover the operator’s back.

METHODS: Protective devices tested (all currently in common use):

table-11

Date of test: 18.07.2015 X-ray equipment: Philips Allura Clarity. Functional clinical suite Dosimeter: Victoreen 451P. Calibration date: May, 2015

Test Phantom patient: Stack of acrylic slabs 38 cm X 38 cm X 24 cm height

Operator Form: Life-size torso model made of a lightweight wooden frame (mostly open space) supported by a support pole (hollow aluminum tube). This serves as a support for the protective garments, which are held in a similar shape, configuration, and location as if worn by a real operator. It also supports the dosimeter which is positioned inside the garment at the level of the abdomen.

Position of Phantom Operator: Positioned at a typical location for an abdominal interventional procedure (see schematic Figs). The dosimeter is located 82 cm from the center of the phantom patient (59 cm along x axis and 57 cm along y axis). The dosimeter height is 112 cm from floor. Measurements were obtained with the dosimeter rotated into several orientations around the clock-face (at 12:00, 1:30, 3:00, 4:30, 6:00, 7:30, 9:00, and 10:30), and the highest value was used. The operator phantom was kept in same location for all different tests with different garments.

Background radiation measurement: <1uSv/h Settings

(dimensions in cm):

SID:        104

FD:         48

Height: 1 (display). 100 cm as measured to floor)

Fluoroscopy: “Fluoro-flavor 1” low dose.

Other shields: 0.5 mm Pb-equiv acrylic hanging shield in typical working position, and with standard table-mounted shielding strips in place.

RESULTS:

Kv=80, mA=18.

table-2rev1graph

CONCLUSIONS: Exposures to operator are highly variable for the different garments. The two highest exposures were for the wrap-around skirt and vest garments with the most complete back coverage. Skirt and vest #3 had incomplete back coverage but provided lower operator exposures than the first two, due to its better attenuation properties. The apron and Zero-gravity ™ have front and side coverage only, but both showed lower exposures than the wrap-around garments presumably due to their higher Pb equivalencies and attenuating properties. This reduction of exposure was most notable for Zero-gravity ™ which may utilize the highest Pb equivalency since it is not supported by the operator. These findings are consistent with the widely accepted concept that exposure to the operator’s back due to secondary scatter from the floors, walls, and other objects in the room is negligible compared to the much larger primary scatter from the patient and table within the beam, which is directed at the front and sides of the operator, and whose attenuation will depend largely on the degree of attenuation by the garment material (1). The radiation passing through the front and sides of the garments is more than the amount which could be scattering to the back from the walls and floors. The decreases in exposure to the head and lower legs where shielding is provided by Zero-Gravity ™, but not by the other garments, was not assessed in this test. The predominant significance of the attenuating capacity of the garment material was also noted in a long-term multi-center clinical study with real patients and operators. Of the multiple factors examined, the two most significant were Pb-equivalency of the garment and case-load (2).

  1. Brateman L. The AAPM/RSNA Physics Tutorial for Residents. Radiation safety considerations for diagnostic radiology personnel. Radiographics 1999;19:1037-1055. http://pubs.rsna.org/doi/full/10.1148/radiographics.19.4.g99jl231037
  2. Marx MV, Niklason L, Mauger EA. Occupational radiation exposure to interventional radiologists: A prospective study. J Vasc Intervent Radiol 1992;3:597-606.

schematic3

FURTHER DISCUSSION:

The results of this study are not surprising in view of previous studies as well as the accepted values for attenuation by varying thicknesses of Pb. Transmission (1-attenuation) of Pb for energies in the spectrum of scattered fluoroscopic x-rays is shown below (data from McCaffree et al [2]).

pb-chart

The reported transmissions for 0.5 mm Pb vs. 1.0 Pb in the graph correlate rather well with the 3.85 fold difference in operator dose-rate between Zero-Gravity ™ and the 0.5 mm Pb lead apron. The 2.4 fold difference between the 0.5 mm Pb lead apron and the 0.35 mm Pb equiv skirt and vest #3 does not seem far out of line with what one might estimate when looking at the above transmission graph although the comparison is somewhat more difficult due to the pure Pb thickness tested. However, the markedly reduced attenuations provided by skirt and vest #1 seems out of line with expected. Possible causes include:

  • Reduced attenuation of the non-lead material below what would be achieved by Pb across the spectrum of scattered energies, and
  • The dependence on frontal overlap for full labeled Pb equivalency which allows higher transmissions at the sides and anterolateral area where much of the scatter is directed at the operator in typical working positions.

Although this study is too small to determine the relative contributions of these two factors, it is likely that both are involved. Many previous reports have already shown that the labeled Pb equivalency of non-lead aprons often poorly reflects actual attenuations of scattered radiation, overestimating them substantially in some cases (3-10). Several authors have recommended that this labeling system be replaced by a more useful and accurate report of the attenuations at several energies across the range seen in scattered diagnostic x-rays (60-120 kv) (4,5,7,8,9-14). This current study supports previous works concluding that the user may not know what to expect from non-lead fabrics with the current labeling system without doing laborious testing of their own as we have done. We strongly encourage all users working near the patient who are considering lightweight garments to test them at several energies regardless of label information. We have not found a highly protective garment which felt light.

 

schematicfrom-cadrevboth-colorv2

(Above) of ways that radiation reaches operator despite protective shielding. The most important is the transmission of frontal and side scatter through the garment, which in turn depends on the attenuating capacity of the material from which it is made.  A very small amount of radiation may also enter from behind in garments with open backs, however this is markedly attenuated by the inverse square law as the the radiation passes to and from an object such as a wall in this sketch, with further attenuation due to the low proportion that is scattered secondarily (about 0.1% to 0.2% at one meter [14]). Consequently, Zero-Gravity ™ with open back showed one-tenth of the exposures to operator (4 uSv/h) than wrap-around garment #2 depicted here (42 uSv/h), mainly due to the 1 mm pb material from which it is made. 

REFERENCES:

1. McCaffrey JP, Shen H , Downton B, Mainegra-Hing E. Radiation attenuation by lead and nonlead materials used in radiation shielding garments. Medical Physics, 2007 Feb; 34 (2):530-7.

2. Muir S, McLeod R, Dove R. Light-weight lead aprons—light on weight, protection, or labeling accuracy? Australas Phys Eng Sci Med 2005 Jun;28(2):128-30.

3. Finnerty M, Brennan PC. Protective aprons in imaging departments: manufacturer stated lead equivalence values require validation. Eur Radiol 2005 Jul;15(7):1477-84.

4. Eder H, Panzer W, Schofer H. Is the lead-equivalent suited for rating protection properties of lead-free radiation protective clothing? Rofo 2005 Mar;177(3):399-404.

5. Vaiciunaite N, Laurikaitis M, Laurikaitiene J, Cerapaite-Trusinkiene R, Adlys G. Verification of lead equivalent for protective aprons used in radiology. Ninth International Conference & Workshop “Medical Physics in the Baltic States” 2011. Available from: http://www.medphys.lt/medphys2011/images/contributions/MedPhys2011_01_03_Vaiciunaite.pdf.

6. Eder H, Schlatt H, Hoeschen C. X-ray protective clothing: does DIN 6857-1 allow an objective comparison between lead-free and lead-composite materials? Rofo 2010 May;182(5):422-8. doi: 10.1055/s-0028-1110000.

7. Christodoulou EG, Goodsitt MM, Larson SC, Darner KL, Satti J, Chan HP. Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter. Med Phys 2003 Jun;30(6):1033-8.

8. Jones AK, Wagner LK. On the futility of measuring the lead equivalence of protective garments. Med Phys 2013 Jun;40(6):063902-2:063902-9. doi: 10.1118/1.4805098.

9. Pichler T, Schopf T, Ennemoser O. Radiation protection clothing in X-ray diagnostics – comparison of attenuation equivalents in narrow beam and inverse broad-beam geometry. Rofo 2011 May;183(5):470-476. doi: 10.1055/s-0029-1245996.

10. Schlattl H, Zankl M, Eder H, Hoeschen C. Shielding properties of lead-free protective clothing and their impact on radiation doses. Med Phys 2007 Nov;34(11):4270-80.

11. McCaffrey JP, Shen H, Downton B, Mainegra-Hing E. Radiation attenuation by lead and nonlead materials used in radiation shielding garments. Med Phys 2007 Feb;34(2):530-537. doi: 10.1118/1.2426404.

12. ASTM International (West Conshohocken, PA). Standard test method for determining the attenuation properties in a primary X-ray beam of materials used to protect against radiation generated during the use of X-ray equipment. Designation F2547-06. Available through http://www.astm.org/Standards/F2547.htm.

13. International Electrotechnical Commission [Internet]. c2014. [cited 2014 Sept 24]. Available from: http://webstore.iec.ch/Webstore/webstore.nsf/ArtNum_PK/49622!opendocument&preview=1.

14. Brateman L. Radiation safety considerations for diagnostic radiology personnel. From: The AAPM/RSNA Physics Tutorial for Residents. Radiographics 1999;19:1037-1055.

Lightweight Aprons EXPOSED

Interventionalists are accustomed to extensive regulations in nearly all aspects of their field, and so are very surprised to discover that the protective quality of their lead aprons is very loosely regulated, resulting in great variation between similarly labeled products. Especially when buying a lightweight non-lead apron, they don’t know what they are getting without complicated laborious in-house testing which is usually beyond their reach. This article outlines the problems and provides some practical tips to avoid the pitfalls that lead to years of silent overexposure.

By Chet R. Rees, MD, Victor Weir, PhD., DABR, Andrew Lichliter, MD, and Evans Heithaus MD

About 40-50% of interventionalists have switched to lightweight “lead” aprons (usually non-lead in reality) to deal with the musculoskeletal problems and fatigue that plague the profession and result in pain, injury, and limitation causing decreased quality of life, and reduction of case-load or disability (1,2). Most are not aware that several studies demonstrate that lightweight aprons don’t fully protect, and they may be receiving radiation exposures several times higher than if wearing standard non-lightweight aprons, despite indistinguishable labels and manufacturer-provided information. For example, one study showed that 73% of 41 aprons tested were outside tolerance levels (4), and there are many others showing the inadequacies of products, standards, and regulations in this industry (3-10). The following example may help frame the problem and its magnitude (Fig 1).

haith-vs-heit

Fig 1. Two aprons are both labeled “0.5 mm Pb equivalent”, with corroboration by their product brochures, websites, and salesmen. They are from different manufacturers but are the same configuration and are almost indistinguishable except by their weights (and color patterns). Yet operator exposure when wearing the lightweight apron on the left was 12 times the operator exposure when wearing the one on the right (appendix A).

How can two aprons with the same label differ so remarkably in their protection? It is due to a combination of loose regulations, optional and outdated standards for testing, and the difference in physical properties for lead and non-lead materials which are often not accounted for in the tests. These problems include:

The radiation attenuation (blocking power) of non-lead materials is very energy dependent (fig 2) (3,5,7-9,13,14). Vendor-reported testing is frequently at only one beam quality (related to energy spectrum), while protection at other important unreported energies to which the operator is being exposed may be lower than expected by label interpretation (9). Think of two pairs of sunglasses which both appear equally dark and protective, but one doesn’t block damaging invisible UV rays, whereas the other pair does. If the labels reported only the ability to block visible light, or red light, or blue light, or any color, the user could not know which pair to buy and could receive UV damage with the first pair. Fortunately, consumers are now protected by sunglass labels which report the UV blockage values. But apron labeling is still outdated and paradoxically aprons have gotten less protective overall than the older ones (which contained lead) because the outdated standards worked well for lead, but not for the more recent non-leads which are often used in lightweight aprons.

w-tungsten-curve

Fig 2.The intensity of radiation behind a tungsten layer shows the high energy-dependency of its attenuation powers. If tested with a beam quality predominantly above 80keV, its Pb equivalency would be far better than if tested in a beam quality predominating in the lower energies. For this reason such non-leads should not be used alone in a protective garment. Filtration properties of the testing beam importantly affect beam quality and must be known.

Attenuating materials, particularly non-leads of lower atomic number, actually emit secondary radiation (or fluorescence) when exposed to radiation. This new radiation reaches the operator and is of biologically damaging energies (19), however is not well detected with the most commonly used testing methods (narrow beam geometry). Use of more appropriate, but not required, testing methods (broad beam or inverse broad beam) would expose the poor protection of the lightweight aprons, despite their labels (5,8-10,13-15).

 

geometry-narrow-beamgeometry-broad-beam

 

 

 

 

 

Fig 3. Narrow beam geometry (left or top). Fluorescent radiation emitted by non-lead test material is not detected by detector so results are falsely favorable. Broad beam geometry (right or bottom) permits detection of the fluorescent radiation which would expose the wearer of the apron, giving more accurate results.

The methods recommended by standards bodies are not required, and are mostly outdated and inadequate. ASTM does not require broad beam geometry and does not provide for Pb equivalency though used on the label. The effects of somewhat improved IEC-616331-1:2014 are unknown and have yet to be realized in commercial products. Manufacturer’s labels continue to be poorly representative of protection, especially for non-leads.

The labels of some vests and skirts specify lead equivalencies that may correspond only to a double layer (overlap zone) without being clear (3). This creates confusion and may lead the user to believe the entire garment is twice its actual thickness.

overlapFig 4. Apron vest is only 0.25 mm Pb, but is labeled as “0.5” because it overlaps to 0.5 in the blue shaded area. However most of the area is not overlapped so radiation transmits through the other areas where the user thought the thickness was twice it’s actual.

overlap-problem

Fig 5. Cross-section views of 2 overlapping aprons. Very different aprons are labeled the same, confusing the buyer who will purchase the lighter one (A) on the left believing they are equal. In fact A is half as thick in front and sides, and user gets more radiation inside apron. “Front” Pb equivalency on label depends on overlap for apron on left, but not for apron B on the right. Although misleading, it is not illegal to label as on the left (A). Other variations occur such as 0.5 on sides with .25 in front giving 0.5 in overlap and sides. Notice scatter often originates eccentrically, so frontal overlap may be less effective. Apron A is non-lead and B contains lead.

aprons-1Fig 6. Side-by-side fluoroscopy of the two aprons A and B shown above in Fig 5. Single thickness of apron B attenuates much better than A although both labelled “0.5 mm Pb equiv”.

aprons-2Fig 7. Aprons A (from Figs 5 and 6) and a new apron C are labeled “0.5 mm Pb” and 0.25 mm Pb” respectively, yet are fairly close in attenuation on a quick fluoroscopy examination. Interestingly, C attenuates slightly better than A, opposite of what one would expect from the labels, and this difference was confirmed on tests performed as described in Fig 6. Both are non-lead. Fluoroscopy of C confirms that is labeled appropriately with regard to “Front” value not relying on overlap.

Substantial weight reductions with equivalent protection have not been achieved for commercial Non-Pb garments, and protection depends largely on weight of the apron for lead and non-lead. Materials that attenuate similarly to Pb over the relevant energy range are still heavy, especially when secondary radiation is measured. Commercial claims of great weight reductions without compromise of protection are made without supporting documentation. This is more recently noted even by manufacturers, such as the statements from one company website that “…there are miniscule differences in the weights of the powders used to produce radiation protection materials…there are no secret formulas…the bottom line here is, it’s lighter weight, it is not offering the same protection levels…Plus or minus a very small percentage, a true 0.5mm [lead equivalent] LE apron is going to weight the same from one manufacturer to the next” (21). Although these facts are becoming more widely understood, under protective aprons are still on the market and need to be avoided.

An excellent study by Pasciak, et al. (22), shows this relationship nicely in their figure 8, where 5 aprons materials were tested along with different thickness of lead foil. Lead foil offered the best protection per weight, and 4 of the 5 aprons fell on a separate line of weight vs. protection which paralleled the pure lead, owing to extra weight due to matrix and fabric. The fifth apron was an outlier; a non-lead with very poor protection per weight. Two aprons met their labels of 0.5 mm equiv (1 non-lead and 1 lead), and the other 3 failed to varying degrees, with as much as ~3X as much exposure to operator. The best protection was provided by the sole lead-based apron. In another study by Lichliter, et al (23), exposure to a phantom operator “wearing” several test aprons was measured while positioned realistically near a phantom patient creating scatter. It had several advantages over previous studies because it tested actual scattered radiation, used a clinically realistic setup, and accounted for differences in the form of the apron (such as open-back vs. closed-back, and differences in how overlap is treated as outlined in Fig 4) rather than just testing scraps of fabric. As seen in Fig 5, weight correlates very well with 1/exposure creating an almost straight line. Data fell along two lines; one for closed-back models and the other for open-back, showing that it is not necessary to cover the back when it is not turned to the patient during fluoroscopy, and that open-back designs are lighter in weight for equivalent protection since they don’t have heavy material in the back. In fact the best protection was provided by an open-back design, Zero-Gravity ™ due to it’s 1.0 mm Pb thickness. Exposures in it were 9.8% of the mean for all aprons, and 37.5% of the best apron. The most protective apron was quite heavy and worn very infrequently in the department.

inv-exp-v-weight

lichliter-setup-photo

Fig 6. Exposure-1 (1/operator-exposure) correlates closely with weight of apron, with most protective aprons being higher on Y axis. There are two main lines; one corresponding to closed-back aprons (skirts and vests), and the other to open-backed aprons (butcher style). Note that the open-backed aprons are lighter for equivalent protection, and the most effective model was the open-backed Zero-Gravity ™ which is shown as 0 weight since it is suspended and can’t be weighed. It is also evident that the lead aprons performed better overall than the non-leads in this group, although with some overlap. Test set-up is pictured on the right, with acrylic stack (phantom patient) producing scatter, and phantom operator on a wood frame with dosimeter inside the chest/abdomen region, standing in a typical position for vascular procedure.

HOW TO BUY AN APRON:

The easiest way to safely buy an apron with reasonable assurance of its protection is to buy a lead or lead-composite apron labeled 0.5 mm Pb equiv which does not feel lightweight, and if it is an overlapping design, check it with fluoroscopy to make certain it is not labeled misleadingly as shown in Figs 4-5. This is done in two ways. First, look for transition points between the back panel and the higher attenuating front panel, which if present, means the frontal Pb equivalency may not depend on overlap (e.g. Apron B in figure 5). If the apron is the same all the way around, as in Apron A of Fig 5, and the label suggests the front is twice the thickness of the back, then the apron is labeled misleadingly and it is probably best to avoid the apron and its manufacturer and vendor. Second, place the new apron side by side under fluoroscopy with an old trusty lead apron that has been tested in the past, and is labeled with the same Pb equivalency. They must be side to side due to the automatic brightness control (separate exams will not work). This test is crude and only under one beam quality but can help to distinguish large differences or misleading labeling based on overlap only.

If you need to cut a little weight, consider an open back “butcher” style apron with a good waist band to take weight off the shoulders. Get lead-based material and make sure it does not feel lightweight. Consider the fluoro test against a trusty known apron to look for gross problems.

If you insist on non-lead, insist on a label designating testing using IEC-616331-1: 2014-05 and IEC-616331-3:2014-05 (they must say 2014 in the titles) and look for the following information: Broad beam geometry (or with inverse broad beam, but NOT with narrow beam) indicated on label. Results of tests at 5 energies ranging from 30-150 kVp or wider using the beam qualities specified in Table 1 of the IEC document. The document is vague on exactly what beam qualities must be used and how to report it, so it is important to check carefully. If not on label, request source documentation which specifies the beam qualities in Table 1 of the IEC document. Unfortunately this document is copyrighted and must be purchased in their web store. It may be nearly impossible to obtain all of this information from the vendor, and as of late 2015 most manufacturers can’t provide all of it even on request (24). Ultimately, the garment should be tested in house by a physicist with a copy of the IEC-616331-1:2014 who has the set-up and knowledge to do this. This will be unavailable at most institutions. Until things change considerably with good validation in the literature, this author strongly advises against lead-free materials, especially since they do not save significant weight even when offering similar protection, and are more likely to be poorly represented by their labels.

If your back or neck is killing you and you can’t do your job without a lightweight apron, be aware that you are probably making a trade-off between weight and radiation protection. It would still be wise to test it against other options in-house using acceptable methods to make certain it is not one of the worst. Even a simple side by side fluoroscopic evaluation may be better than nothing, but the value of this has not been established.

Regulations are unlikely to change soon, and the standards are not preventing high variability of products. The only way to remedy these problems are to police the manufacturers and vendors ourselves by demanding copious technical information, making careful choices, and testing and rejecting aprons and vendors who can’t provide information or who provide misleading information.

About the author: Chet R. Rees, MD is a practicing interventional radiologist and Clinical Professor in Dallas, TX at the Baylor Scott and White Hospital. He discloses no conflict of interest in the protective apron industry. He discloses a financial interest with CFI Medical Solutions, who makes shielding products including the Zero-Gravity ™ suspended radiation protection system.

 

FAQ

  1. Q: Do substantially lightweight aprons provide adequate protection? A: No, not even when the label implies they can. There is no miracle material which dramatically cuts weight without making sacrifices in protection. The literature has shown that modest weight reductions may be achieved by mixing metals compared to using pure lead, but substantial weight reductions for same protection has been an elusive goal, despite the appearances of labels and manufacturer’s claims.
  2. Q: Does the “0.5 mm Pb equivalent” label on my apron mean I am protected? A: If your apron contains lead and it is not lightweight, it probably does mean you are getting the protection close to what you were expecting based on the label. But if your apron is non-lead, such labels usually do not guarantee such protection.
  3. Q: Is there any type of label I can trust for non-leads? A: Maybe, time will tell. The IEC-616331-1:2014 (it must say 2014 in the title) standards have incorporated some improved methods including inverse broad beam geometry and suggestion for multiple energies. However whether these are used, followed as intended, or how the results compare to independent tests are a still unknown. This author has never seen a full IEC-616331-1:2014 label on any product despite frequent checks at vendors booths.
  4. Q: Are all non-lead aprons terrible? A: No. Some models are not lightweight, use a good mixture of metals to provide attenuation over a spectrum of energies, and include enough to be effective. Based on reports, this seems to be the minority. Current labeling and marketing information are not very helpful, but picking them up and feeling their weight is a pretty good indicator. Unfortunately again, studies have shown that some non-lead aprons provide less protection even on a per weight basis, in addition to the loss of protection due to being lightweight, thereby being especially poor (22,23).
  5. Q: How do I test my apron to be sure I am okay? A: If your apron contains lead and is not lightweight, it is probably okay, but you can test at a couple beam qualities using narrow or broad beam geometry which may be available to your physicist and compare results to the attenuation tables and Pb equivalency tables, or test against a known standard. Fluoroscope any overlapping models to make sure the labeled attenuation does not correspond to overlap zone only. If your apron is non-lead, it may be difficult or impossible for you to get it done in house. Set up a broad beam geometry, and use 5 beam qualities ranging from 30-150 kVp with the beam filtration values shown in the tables in IEC-616331-1:2014. Compare results to the attenuation tables and Pb equivalency tables. Fluoroscope any overlapping models to make sure the labeled attenuation does not correspond to overlap zone only.
  6. This stuff scares me. How can we fix this? A: Major changes in regulations could help but will not happen anytime soon. Rapid change is possible through user awareness and demands made upon vendors. If physicians and other workers refuse to buy from vendors whose aprons haven’t been tested in rigorous ways with test values and conditions indelibly attached to the garment, then some vendors will provide the necessary information, it will be more accurate, and the quality of their aprons will have to improve since under-performing models will be exposed. Vendors who don’t do this will probably continue but at least the user will have a choice they do not have right now.
  7. Q: Why do manufacturers use non-leads to make lightweight aprons if non-leads aren’t really significantly more protective per weight? Why not just use thinner lead preparations? A: We can’t know the intentions, but we can state a couple things which might lead to this. First, commonly used testing such as with narrow beam geometry and use of one or two beam qualities are reasonably accurate for lead but not for non-leads; a poorly protective lightweight non-lead apron could slip through the cracks and get a 0.5 mm Pb label much more easily than a poorly protective lightweight lead apron. Second, lightweight aprons sell, they are in demand, and can command higher prices which may lead to higher profit margins. The buyer may easily believe that non-leads are lighter than lead and so can therefore make lighter aprons (when in fact aprons can easily be made to any weight using any substance in different amounts). Taken all together, the users can easily go down the intuitive, but incorrect, path that lighter materials are more efficient and make protective lightweight aprons which they should pay more money to obtain. And the sellers are simply offering what the people want, without violating any regulations or laws. The cycle can only be broken by user awareness and demands made upon vendors so that profits come to those providing good solid protection with complete and appropriate test results, not from well marketed lightweight aprons which protect worse than evident from label.
  8. Q: Is there any use for a lightweight apron? A: Probably yes. Some personnel don’t get very close to the patient (source of scatter radiation) during procedures, such as a circulating technologist who is usually behind the control panel. The inverse square law reduces the field in their location enough such that 0.5 mm Pb equivalency is not required. However, they should still be able to assess their purchases by label and brochure without taking wild guesses as to actual protection. For example, settling for 0.25 mm Pb equivalency but getting something less is not acceptable. Interventionalists standing near the patient should be using 0.5 mm Pb equiv without deficiencies.
  9. Q: Weren’t there studies that showed that non-lead bilayers could substantially lower weight without loss of attenuation? A: Two studies raised hopes of 25% weight reduction with equivalent attenuation, however these were experimental, included non-commercial metals and computer-based simulations (13,15). The authors noted that actual attenuating capabilities must be measured in the final product since it is influenced by the matrix materials and other manufacturing factors which they did not account for. Such findings in commercially available aprons have not been demonstrated to our knowledge.

REFERENCES

1. Klein, LW, Tra Y, Garratt KN, et al. Occupational health hazards of interventional cardiologists in the current decade. Catheterization and Cardiovascular Interventions 2015. 86 (5) 913-924, November 1.

2. Ross AM, Segal J, Borenstein D, Jenkins E, Cho S. Prevalence of spinal disc disease among interventional cardiologists. Am J Cardiol. 1997 Jan 1;79(1):68-70.

3. Muir S, McLeod R, Dove R. Light-weight lead aprons—light on weight, protection, or labeling accuracy? Australas Phys Eng Sci Med 2005 Jun;28(2):128-30.

4. Finnerty M, Brennan PC. Protective aprons in imaging departments: manufacturer stated lead equivalence values require validation. Eur Radiol 2005 Jul;15(7):1477-84.

5. Eder H, Panzer W, Schofer H. Is the lead-equivalent suited for rating protection properties of lead-free radiation protective clothing? Rofo 2005 Mar;177(3):399-404.

6. Vaiciunaite N, Laurikaitis M, Laurikaitiene J, Cerapaite-Trusinkiene R, Adlys G. Verification of lead equivalent for protective aprons used in radiology. Ninth International Conference & Workshop “Medical Physics in the Baltic States” 2011. Available from: http://www.medphys.lt/medphys2011/images/contributions/MedPhys2011_01_03_Vaiciunaite.pdf.

7. Eder H, Schlatt H, Hoeschen C. X-ray protective clothing: does DIN 6857-1 allow an objective comparison between lead-free and lead-composite materials? Rofo 2010 May;182(5):422-8. doi: 10.1055/s-0028-1110000.

8. Christodoulou EG, Goodsitt MM, Larson SC, Darner KL, Satti J, Chan HP. Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter. Med Phys 2003 Jun;30(6):1033-8.

9. Jones AK, Wagner LK. On the futility of measuring the lead equivalence of protective garments. Med Phys 2013 Jun;40(6):063902-2:063902-9. doi: 10.1118/1.4805098.

10. Pichler T, Schopf T, Ennemoser O. Radiation protection clothing in X-ray diagnostics – comparison of attenuation equivalents in narrow beam and inverse broad-beam geometry. Rofo 2011 May;183(5):470-476. doi: 10.1055/s-0029-1245996.

11. US Food and Drug Administration [Internet]. Silver Springs (MD) [updated 2014 Sept 1; cited 2014 Sept 24]. Available from: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=892.6500.

12. INFAB Corp [Internet]. [cited 2014 Sept 24]. A challenge to BLOX-R and a warning to anyone involved in the use or procurement of flexible radiation materials. Available from: http://www.infabcorp.com/open-letter-to-bloxr/.

13. McCaffrey JP, Mainegra-Hing E, Shen S. Optimizing non-PB radiation shielding materials using bilayers. Med Phys 2009 Dec;36(12):5586-5594.

14. Schlattl H, Zankl M, Eder H, Hoeschen C. Shielding properties of lead-free protective clothing and their impact on radiation doses. Med Phys 2007 Nov;34(11):4270-80.

15. McCaffrey JP, Tessier F, Shen H. Radiation shielding materials and radiation scatter effects for interventional radiology (IR) physicians. Med Phys 2012 Jul;39(7):4537-4546. doi: 10.1118/1.4730504.

16. McCaffrey JP, Shen H, Downton B, Mainegra-Hing E. Radiation attenuation by lead and nonlead materials used in radiation shielding garments. Med Phys 2007 Feb;34(2):530-537. doi: 10.1118/1.2426404.

17. ASTM International (West Conshohocken, PA). Standard test method for determining the attenuation properties in a primary X-ray beam of materials used to protect against radiation generated during the use of X-ray equipment. Designation F2547-06. Available through http://www.astm.org/Standards/F2547.htm.

18. International Electrotechnical Commission [Internet]. c2014. [cited 2014 Sept 24]. Available from: http://webstore.iec.ch/Webstore/webstore.nsf/ArtNum_PK/49622!opendocument&preview=1.

19. 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 Sept;32(3):129-139. doi: 10.1088/0952-4746/32/3/N129.

20. Akber SF, Das IJ, Kehwar TS. Broad beam attenuation measurements in lead in kilovoltage X-ray beams. Med Phys 2008;18:197–202. doi: 10.1016/j.zemedi.2008.04.008.

21. http://www.infabcorp.com/is-your-lead-apron-protecting-you/  Access date 2-23-2016.

22. Pasciak AS, Jones AK, Wagner LK. Application of the diagnostic radiological index of protection to protective garments. Med Phys 42 (2), February 2015. 653-662.

23. Lichliter A, Gipson S, Heithaus E, Syed A, Weir V, West J. Clinical evaluation of protective garments with respect to garment characteristics and manufacturer label information. Presentation and poster at the International Symposium on Endovascular Therapy (ISET) 2016, February 6-10, Hollywood Florida. Abstract: J Vasc Interv Radiol 2016;27:e1-e21, page e1-e2. http://www.jvir.org/article/S1051-0443%2816%2900020-8/pdf Abstract and Poster: https://www.eventscribe.com/2016/posters/ISETCIO/SplitViewer.asp?PID=MjYyNjA1MDAyNQ

24. Heithaus RE, Onofrio A, Weir V, Rees CR. Can aprons be properly evaluated for their protective quality without in-house validation? Poster at the International Symposium on Endovascular Therapy (ISET) 2016, February 6-10, Hollywood Florida. Abstract: J Vasc Interv Radiol 2016;27:e1-e21, page e11. http://www.jvir.org/article/S1051-0443%2816%2900020-8/pdf Abstract and Poster: https://www.eventscribe.com/2016/posters/ISETCIO/SplitViewer.asp?PID=MjYyNjg3MDAwOQ

Beware the “Lightweight Lead Apron”

Author’s note: This current discussion is intended to be relatively detailed with more specific citation support, and refers to the other link for practical recommendations. A relatively short and practical guide is available at this link: Link to “Lightweight Aprons Exposed”

The regulations for testing and labeling of X-ray protective clothing are surprisingly lax (13, 30). We don’t know what we are getting without laborious in-house testing, especially with the newer non-lead or lightweight varieties (3, 6, 2, 4). Claims of light weight protective lead equivalent aprons are followed by disappointment as the true results become known. The strong energy-dependency of attenuation, which is very different for the non-leads relative to lead (3, 1, 2, 4, 15, 16, 5, 17) and the importance of testing non-leads with broad beam geometry to detect the secondary fluorescent radiation that they produce (1, 4, 15, 19, 16, 5, 18) means that many non-leads are reported at energies and geometries that allow their Pb equivalence to be overstated on the label (15). Non-lead materials are not providing the results that were expected of them unless they too are made into heavy aprons, and even then the protection can be erratic and counter to label. Interventionalists must exercise great caution as they balance comfort vs. protection

Busy interventionalists need good protective shielding, generally accepted to be at least equivalent to 0.5 mm Pb. Although imaging chain advances have caused reductions in dose/minute, operator doses are pushed up over recent years and decades by more specialized practices and continually increasing complexity of procedures. Radial access increased fluoroscopy times (20), and very intensive procedures such as TAVR and fenestrated EVAR are now common. Often overlooked is the huge impact of the worldwide obesity epidemic (21,22) since larger patients cause several-fold increases in operator exposure, described in one study to be 8.4X when increasing patient thickness from 24 to 34 cm (23). Lifetime operator doses are generally unknown since they are not tracked as interventionalists move between institutions and jobs, compliance with consistent badge-wearing is as low as 63% (24), and under-lead badges are frequently not used. It is incumbent on the interventionalist to make certain they are adequately protected with suitable protective clothing, yet the products are less protective than they were in the past as manufacturers sell large numbers of lightweight aprons, frequently without lead, which pass through the loose regulatory system without providing the protection that users believed they were receiving. They only way to insure adequate self-protection is to gain an understanding of the principles and take precautions as outlined in this discussion and elsewhere (Link to “Lightweight Aprons Exposed”). The only fast way to improve the problem at large, since regulations are very unlikely to change enough in the near future, is to become picky customers who force vendors to provide more information than required by law in order to earn their sales.

When tested independently by academic physicists using methods which are more accurate than those routinely performed by manufacturers and hospital physicists or RSO’s, lightweight aprons frequently underperformed relative to their labels (3, 6, 1, 7, 2, 4, 15, 17, 25) causing some authors to recommend internal validation (6, 7, 4, 17, 25, 26). In one report, 73% of 41 aprons were outside tolerance levels, with discordance between label and actual Pb equivalency in 3 of 4 manufacturers (6). Another study found the non-lead aprons to provide 70% lower attenuations compared to lead-based models, especially below 80kVp (1). This is especially concerning since these lower energies are particularly hazardous biologically (27). Another study confirmed higher than labeled transmissions for two non-leads ranging from 61% to 478% that of a lead apron, most markedly at the quality of 60 kVp (15). Studies have shown that protection depends on the weight of the garments, or more specifically the areal density (mass per area) (17, 25). Reducing weight through use of non-leads or using too little attenuating elements in the matrix of the apron causes attenuation to decrease, even when not reflected by the Pb equivalency rating on the label (a value which many think should be abolished in favor of reporting of transmission values) (17, 25). In one of the best studies on the subject, it was shown that lightweight non-lead garments were lighter because they provided lower protection, and not due to more efficient attenuation on a weight basis (17).

interventcoFigure 1. DRIP (an index of protection) vs. areal density (a correlate of weight of apron). The best protection per weight is provided by pure lead strips of varying thicknesses. Aprons are heavier due to matrix, fabric, and other structural components. Most aprons fell along a curve which roughly paralleled the one for lead foil, moved slightly to the right due to the mass of structural materials. The best protection was by the single lead (“L”) apron on the lower right. One non-lead (”NL”) apron demonstrated the Pb equivalency of its label and was close in density and protection to the L apron (lower right). The other 3 NL fell short of their labeled protection and were also less dense. Two of these were along the curve indicating their deficiency of protection was probably simply related to their lower weight. However the position of the outlier, off the curve to the right, indicates it is more poorly protective per weight than the lead or other non-lead aprons. Such outliers are the most concerning since an apron of such material could be sub-optimal in protection even if not lightweight. (Figure reproduced and modified from [17] with permission).

Since users are not being protected by regulations, and radiation safety officers often have their hands full trying to meet regulations without extra time to perform laborious tests, it becomes necessary for the user to understand some physics in order to make sure they are protected. There are two main principles playing roles; the different patterns of energy dependency of attenuation for the different metals, and the emission of fluorescent secondary radiation by different metals when exposed to certain energies found in scattered x-rays. This fluorescent radiation requires broad-beam geometry for detection in order to prevent overestimation of a material’s protective capability. It is also important to be aware that the labeled Pb equivalency of some aprons corresponds only to the overlapped zones without being declared.

Attenuating capabilities over the 30-150keV range of interest for the materials used in aprons is highly energy dependent (3, 1, 2, 4, 15, 16, 5, 18, 17). This is in large part due to the photoelectric effect, with the various metals having their own different k-absorption edges and emission lines (16). It is commonly known that the protection with lead-free aprons is strongly associated with beam quality, including the study showing the penetration through one lead-free garment at 60 kVp was 478% higher than the penetration for the lead-based garment of similarly labeled Pb equivalency (15). Whereas Pb and the non-Pb apron materials may be equivalent at one beam quality measured by manufacturer, they may be very greatly different at others to which the operator is constantly being exposed (3, 1, 2, 4, 15, 16, 5). These factors can cause great overestimation of the protective capability of many aprons, especially non-lead. As said nicely in one report: “…as lead has been replaced by other elements, verifying manufacturers’ claims regarding the lead equivalence of such garments has become nearly impossible, and current standards only require measurement of attenuation or lead equivalence at a single beam quality. A garment may provide a high degree of protection at the specified beam quality, but underperform at others.” (15).

These differences can be used to advantage in the mixtures of materials with lead (4) to reduce weight slightly without substantial loss of protection compared to pure lead, but lightweight non-lead preparations have led to the disappointing results described above.

When apron materials, particularly the non-leads of lower atomic number, are exposed to the scatter radiation field, they emit a new secondary radiation called fluorescence, which is typically of lower, biologically damaging energies that penetrate the shallow organs such as breast tissue, male gonads, thyroid, and skin (1, 4, 5, 15, 19, 16, 5, 18, 27, 28). This secondary radiation is most important for shields near the body, such as aprons (5). The relative biological effectiveness (RBE) of transmitted and secondary radiations can be doubled with some non-leads compared to lead materials (27). This difference was shown to be more pronounced at lower transmission values (28) when the user may be the least concerned. Narrow-beam geometry testing (Link to figure of narrow beam) is the most commonly used and simplest setup for testing apron materials, but does not detect this fluorescent radiation, and therefore overestimates the attenuation profiles of many non-lead aprons (1, 4, 15, 19, 16, 5, 18). Fluorescence is detected with broad-beam geometry Link to figure of broad beam which is less commonly available and not required for labeling (1, 4, 15, 19, 16, 5, 18). Any apron which is not predominantly lead based should be tested under broad beam geometry and explicitly stated on the label. A German study showed that three lead-free aprons which passed manufacturer criteria failed to fulfill the criteria when tested according to the recommended but optional German DIN 6857-1 standards, and that the only apron which passed was lead-based (2). Non-lead bilayers were designed to minimize the fluorescent effect, but one study of such a preparation showed 20-30% higher air kerma transmissions for surface radiation compared to penetrating radiation (16). Narrow beam testing was adequate in the past when aprons were all predominantly lead but should be eliminated in modern day since it is used inappropriately, albeit legally, with the user suffering the consequences.

The following example occurred in our department. A physician colleague purchased a lightweight skirt and vest to help with his back pain, after assurances from the salesman that it was rigorously tested to earn its labeled Pb equivalency of 0.5 mm front and 0.25 mm back. Intrigued by its lightness, we performed a crude test using an electronic dosimeter and compared the front of the vest to another heavier lead apron which was also labeled 0.5 mm Pb in front. Surprised by the difference, we passed the vest to our physicist for official testing and comparison to 2 other aprons, with the following results:

Figure 1. Transmission of x-rays at 80 kVp narrow beam geometry:

transmission-of-xrays-at-100kvp-narrow-beam-geometry-updated

“Lightweight” vest labeled (0.5 mm Pb equiv): 13.9%
Control apron (labeled 0.5 mm Pb equiv): 1.3%
Fabric from Zero-Gravity™ suspended system (labeled 1.0 mm Pb equiv): 0.5%

The lightweight vest allowed 10.7 X the radiation transmission compared to the control apron, yet both were labeled as having 0.5 mm Pb equivalency. This large difference is shocking to somebody who might have spent hundreds or thousands of hours in such an apron, thinking it was equivalent to another apron because both were “equivalent” to 0.5 mm Pb on their labels.

The discrepancy can be due to a combination of the factors described above, possible poor testing quality, and another common cause: some manufacturers label Pb equivalency based on overlap of front flaps. In other words, it may only apply to the segment where overlap occurs, without disclosure by label, website, or salesman. The thickness is therefore only ½ as much as the user expected. Since the preponderance of the vest and skirt are not overlapped during use, including the anterolateral portion where a large proportion of the scatter enters during most vascular procedures, exposure may be much higher than expected. We examined the vest under fluoroscopy, demonstrating that the back and front were the same attenuation despite being labeled as different, and both were much lower in attenuation than the other apron. The simple way to determine this is described in Link to “Lightweight Aprons Exposed”

But even when tested overlapped, the lightweight vest still under-performed by a factor of 3-fold transmission (3.9% vs 1.3%) compared to a non-overlapped standard apron labeled at the same lead equivalency, and may have fared even more poorly if tests using broad beam geometry at multiple energies were performed.

A single thickness of the material from a Zero-Gravity ™ suspended radiation protection unit (labeled 1.0 mm Pb equiv) was tested using the same equipment and method described above, showing a transmission of  0.5%. This attenuated 27.8X better than the lightweight vest where it is not overlapped, 7.8X the lightweight vest when doubled over, and 2.6X as well as the 0.5 mm Pb control apron. A large study examining many methods and shielding habits showed that the presence of 1 mm Pb protective garment was the single greatest determinant of total body exposure besides caseload, reducing under-garment exposures by 2/3 (9).

Another way to cut weight in an apron is to skimp on the binding matrix and structural components. This can lead to breakdown and diminished attenuation. A lightweight apron was used for many procedures over years in our department. Upon periodic integrity check, the attenuating materials had substantially shifted, leaving large patches of poor protection. This was much to the dismay of the apron’s user, who wondered how many hours of fluoroscopy were performed in this condition before discovery. Aprons have different methods of binding the attenuating materials which should be considered, and integrity checks performed regularly (10).

Many factors have set the stage for confusion and discrepancies between labels and true performance. Regulations and reporting requirements are very loose, completely counter to the expectations of interventionalists who are accustomed to the strict regulations surrounding patient-related products and policies. Testing and reporting standards are outdated, inadequate, optional, and way too confusing to be understood by users, in addition to being copyrighted and lawfully available only by individual purchase. Citations of such standards by the vendors gives users a false sense of confidence about the products which nevertheless vary greatly in protection despite identically labeled Pb equivalency values. Users may be desperate to believe in promises of “lightest aprons on the market” or amazing proprietary fabrics because they are having discomfort, pain or worries about disability, but in reality miracle products don’t exist and a few basic metal compounds are used. There is a large gap between perception: I am protected because the label says 0.5 m mPb, there are certificates posted all over the website, and regulatory bodies are making sure it’s all meaningful –and the reality: regulations are almost non-existent, and the certificates and label don’t change the fact that the lightweight apron protects far less than the heavier one.

Regulations: Radiation protective clothing is an FDA Class I device, the lowest possible (17). Regulators reserve the right to audit manufacturers’ claims, but manufacturers are essentially self-policing. While radiation safety officers (RSO) periodically surveille aprons, vests, and skirts for defects such as tears and holes, the shielding power, arguably the most important component of the apron, is usually taken from the manufacturer’s labels at face value.  The RSO may test the apron’s attenuating power when asked, however, this is not performed routinely and most will not have the means to provide truly meaningful data for all types of aprons. The awareness of the problems with lightweight and non-lead aprons comes nearly entirely from independent academic study and reporting in peer-reviewed medical physics journals, not from regulatory oversight.

Standards: Standards are available for purchase under copyright so are not viewable to most users or even their RSO’s. Manufacturers buy them and have the option to choose which to use, if any. They may contract unregulated third parties to do the testing. So the certificates claimed by manufacturers are not from centralized regulatory bodies or the standards bodies. The standards arose with lead-based aprons and work reasonably well for them, but not for non-lead models as explained in detail below. They provide many options for how to test and report, and some options are not considered appropriate for non-lead lightweight aprons by several authors. The testing is of small patches of material and not on actual aprons, so considerations due to configuration, such as overlap, are not accounted for, causing misleading results as explained below. It is possible for a material to be tested according to a standard such as ASTM (8) with regard to attenuation values which the user may not be able to find or understand, while the label is reported in Pb equivalency, which can grossly overestimate protection and, according to ASTM is not provided for in their standards and not recommended as noted in their statement: “Although lead equivalency has been the standard for reporting protective material capability, the drafters of this test method believe it is not feasible to obtain adequate standard lead samples for reporting lead equivalency values.”(8) Other criticisms of ASTM (designation F 2547-06): energy range is not broad enough (should include lower and higher kVp’s), uses direct beam whereas operators are exposed to scatter of a different quality, uses excessive beam hardening, permits use of narrow-beam geometry which can grossly underestimate exposure (see below), provides vague description of test setup. DIN standards are written in German. IEC standards (29) have recently been improved to some degree (IEC-616331-1: 2014-05 and IEC-616331-3:2014-05 [must have “2014” in title]). IEC-616331-1: 2014-05 is sometimes cited without  IEC-616331-3:2014-05, leaving out much of the requirements specific to aprons and other garments, and permitting narrow beam geometry and as few as 2 radiation qualities defining a range, selected from a broader table. IEC-616331-3:2014-05 should be cited also, but is only properly done in compliance with the document when the report includes name of manufacturer or supplier, designation of type of apron, lead equivalent, x-ray tube voltage range which should be 50-110kV, area density of fabric in the garment, and “IEC 61331-3:2014” exactly as stated here. Absence of any of this information, marked clearly and permanently on the garment, indicates non-compliance with this standard. Also required on accompanying documents (not on the garment itself) is specific information about the size of and length and portions of body covered. This author has not seen such labels on garments at trade meetings in the U.S. Because compliance is optional and confusion exists, we recommend the buyer request written attestation for non-lead garments that the lead equivalents were tested with inverse broad beam geometry or broad beam geometry, with specific lead equivalents at each beam quality of 50, 70, 90, and 110 kv. And that anything labeled “front” covers 60% of the circumference of the body of a user who fits the garment (approximately from left to right posterior axillary lines). Although a step in the right direction, the problems are far from solved and the effects of these optional standards on actual product quality will take years before independent academic studies can determine if they have had any substantial effect.

Even if the standards were stricter, they still wouldn’t prevent a common cause of misunderstanding. Manufacturers make claims such as “certified to the exacting standards of [IEC or AST or DIN], leading to the misperception that these organizations require certain results to be achieved 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. Moreover, the standards do not require any certain results to be achieved; they do not describe a bar over which the product must clear. The results could be terrible, with very poor attenuation, yet still be in accordance with the “exacting” standards described. A piece of cardboard could be tested by nearly anybody in his own lab, who then provided a “certificate” indicating that he followed the guidelines of IEC or ASTM or DIN. The manufacturer might then claim that the piece of cardboard was “certified to the exacting [e.g. IEC] standards…” though its attenuation was essentially 0. For a real apron product, any existing certificate is probably created and signed by a member of the company or somebody they hired to test for them. These certificates are not required to become public and are often very difficult or impossible to extract from the manufacturers. Once obtained, it is still often difficult to tell if the apron you are considering is made from the material described in the certificate, or whether the thickness of material tested corresponds to the exact thickness of the apron, since most are constructed of a number of layers of the material, and that number is not disclosed with regard to the apron. Upon inquiry, the vendor’s representatives often don’t know the answer, and more inquiries to actual shop people are needed for informal and verbal results provided by the more helpful manufacturers. Also, the certificates are not for the aprons themselves, they are just for the material fragments tested, so whatever process of configuration or manufacture which might affect protection is not reflected.

In summary, determination of protective capability of an apron from vendor supplied information requires the diligence and shrewdness of a detective in order to succeed in only some of the cases (26). Self-testing, although laborious, seems to be the only way if one wants to venture towards lighter products or non-lead aprons. Hopefully someday each apron will have a permanently attached label giving all the information necessary to determine its protection, the information will be reliable, and there will be substantial repercussions to manufacturers or testers providing inaccurate or inconsistent information.

Many authors have called for changes in the testing and reporting standards (15, 6, 1, 2, 4, 5, 12, 17). The concept of Pb equivalency is no longer useful with the non-leads being used today with all the problems of comparing to lead described above, in addition to the difficulties in finding lead samples for comparison (17). The use of attenuation values is better, but would need to be available for all products to allow comparisons, and does not clearly give the user a good understanding of the apron without comparisons or charts of values for accepted standards. The best method would be to report transmission values at the various beam qualities (kVp’s and spectral descriptions), supplied with comparisons to lead for easy reference, since the transmitted radiation is what exposes the user (17, 25). This allows the user to easily see how much radiation they would receive with one product vs. another, or vs. a Pb equivalency standard. For example, a difference in attenuation from 99% to 94% may not sound like much, but it would mean that the user would receive 6X as much transmitted radiation for one vs the other. Other changes would include the requirement, not the option, to report at 30 kVp, 150 kVp, and three intermediate values which are consistent for all products, using standardized beam filtration qualities. Broad beam or inverse beam geometry should be mandatory. Values should not apply to double thickness in the overlap zones unless the overlap zones are complete from neck to bottom and from the poster axillary line on one side to the other for the largest person who might wear that size of apron. It should be mandatory to report the test values and the manner of labeling overlap on the label with enough information so that the user can be assured all of the above procedures were followed. IEC-616331-1: 2014-05 and IEC-616331-3:2014-05 have taken steps in these directions but not far enough, and leaving too many choices to the testers so that not all must be followed and comparisons for aprons tested in different ways are still difficult. Also the standards must be mandatory to be effective. Consideration of methods which emulate the actual scatter beam qualities of the real environment would be an excellent final step (15, 17).

With all the challenges still in place, choosing an apron is still very difficult. Guidelines are available at Link to “Lightweight Aprons Exposed”. In short, the simplest way to be reasonably assured of adequate protection is to buy an apron which is predominantly lead, with Pb equivalency rating of 0.5 mm, and to make certain that rating does not apply only to the overlapped portion, which may require careful fluoroscopy and comparison to an available standard as described in Link to “Lightweight Aprons Exposed”. If it feels good, test it;  a light apron is a tip-off that something is wrong, since the lighter ones test unfavorably when tested carefully as in the references cited. If an apron feels heavy, it will usually provide the protection as labeled, although for some non-leads there is still some risk that its protection may be lower than expected, corresponding to the outliers that have been encountered in some studies (17, 25).

The message of ALARA (As Low As Reasonably Achievable) for the interventionalists is not to use regulatory limits to set our dose goals because we should strive to be well below them.   Individual interventionalists are encouraged to work towards a safer environment for themselves and advocate for improved protection.

APPENDIX A:

Appendix Table A.  Effective transmission (%) with pure lead (Pb) by radiation quality.  From (12) unless otherwise indicated in superscript:

kVp 0.25 mm Pb 0.50 mm Pb 1.0 mm  Pb 2.0 mm  Pb
60 4.3% 0.4 0.01 0
70 5.44 0.94
80 12 2.6 0.27 0.01
100 15416.7 545 0.9 0.05
120 20 6.3 1.1 0.06

Appendix Figure A. Table A in graph form.

pb-chart

REFERENCES:

1. Eder H, Panzer W, Schofer H. Is the lead-equivalent suited for rating protection properties of lead-free radiation protective clothing? Rofo 2005 Mar:177(3):399-404.

2. Eder H, Schlatt H, Hoeschen C. X-ray protective clothing: does DIN 6857-1 allow an objective comparison between lead-free and lead-composite materials?

3. Muir S, McLeod R, Dove R. Light-weight lead aprons—light on weight, protection, or labeling accuracy? Australas Phys Engl Sci Med 2005 Jun;28(2):128-30.

4. Christodoulou EG, Goodsitt MM, Larson SC, Darner KL, Satti J, Chan HP. Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter. Med Phys 2003 Jun;30(6):1033-8.

5. Schlattl H, Zankl M, Eder H, Hoeschen C. Shielding properties of lead-free protective clothing and their impact on radiation doses. Med Phys 2007 Nov;34(11):4270-80.

6. Finnerty M, Brennan PC. Protective aprons in imaging departments: manufacturer stated lead equivalence values require validation. Eur Radiol 2005 Jul;15(7):1477-84.

7. Vaiciunaite N, Laurikaitis M, Laurikaitiene J, Cerapaite-Trusinkiene R, Adlys G. Verification of lead equivalent for protective aprons used in radiology. Ninth International Conference & Workshop “Medical Physics in the Baltic States” 2011. Available from: http://www.medphys.lt/medphys2011/images/contributions/MedPhys2011_01_03_Vaiciunaite.pdf.

8. ASTM International. Standard test method for determining the attenuation properties in a primary X-ray beam of materials used to protect against radiation generated during the use of X-ray equipment. Designation F2547-06. Available through www.astm.org.

9. Marx MV, Nilason L, Mauger EA. Occupational radiation exposure to interventional radiologists: A prospective study. J Vasc Intervent Radiol, 1992; 3:597-606.

10. Stam W, Pillay M. Inspection of lead aprons: a practical rejection model. Health Physics 2008 Aug;95 Suppl 2:S133-6.

11. Zuguchi M, Chida K, Taura M, et al. Usefulness of non-lead aprons in radiation protection for physicians performing interventional procedures. Radiat Prot Dosimetry 2008;131(4):531-4.

12. McCaffrey JP, Shen H , Downton B, Mainegra-Hing E. Radiation attenuation by lead and nonlead materials used in radiation shielding garments. Medical Physics, 2007 Feb; 34 (2):530-

13. US Food and Drug Administration [Internet]. Silver Springs (MD) [updated 2014 Sept 1; cited 2014 Sept 24]. Available from: http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=892.6500.

14. INFAB Corp [Internet]. [cited 2014 Sept 24]. A challenge to BLOX-R and a warning to anyone involved in the use or procurement of flexible radiation materials. Available from: http://www.infabcorp.com/open-letter-to-bloxr/.

15. Jones AK, Wagner LK. On the futility of measuring the lead equivalence of protective garments. Med Phys 2013 Jun;40(6):063902-2:063902-9. doi: 10.1118/1.4805098.

16. McCaffrey JP, Mainegra-Hing E, Shen S. Optimizing non-PB radiation shielding materials using bilayers. Med Phys 2009 Dec;36(12):5586-5594.

17. Pasciak AS, Jones AK, Wagner LK. Application of the diagnostic radiological index of protection to protective garments. Med Phys Vol 42 (2) Feb 2015: 653-662.

18. McCaffrey JP, Tessier F, Shen H. Radiation shielding materials and radiation scatter effects for interventional radiology (IR) physicians. Med Phys 2012 Jul;39(7):4537-4546. doi: 10.1118/1.4730504. nts. Med Phys 42(2) Feb 2015: 653-662.

19. Pichler T, Schopf T, Ennemoser O. Radiation protection clothing in X-ray diagnostics – comparison of attenuation equivalents in narrow beam and inverse broad-beam geometry. Rofo 2011 May;183(5):470-476. doi: 10.1055/s-0029-1245996.

20. Feldman DN, Swaminathan RV, Kaltenbach LA, Baklanov DV, Kim LK, Wong SC, Minutello RM, Messenger JC, Moussa I, Garratt KN, Piana RN, Hillegass WB, Cohen MG, Gilchrist IC, Rao SV. Adoption of radial access and comparison of outcomes to femoral access in percutaneous coronary intervention: An updated report from the national cardiovascular data registry (2007–2012). Circulation 2013;127:2295–2306.

21. Centers for Disease Control and Prevention [Internet]. Atlanta (GA) [updated 2014 Sept 9; cited 2014 Sep 24]. Available from: http://www.cdc.gov/obesity/data/adult.html.

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24. Klein, LW, Tra Y, Garratt KN, et al. Occupational health hazards of interventional cardiologists in the current decade. Catheterization and Cardiovascular Interventions 2015. 86 (5) 913-924, November 1.

25. Lichliter A, Gipson S, Heithaus E, Syed A, Weir V, West J. Clinical evaluation of protective garments with respect to garment characteristics and manufacturer label information. Presentation and poster at the International Symposium on Endovascular Therapy (ISET) 2016, February 6-10, Hollywood Florida. Abstract: J Vasc Interv Radiol 2016;27:e1-e21, page e1-e2. http://www.jvir.org/article/S1051-0443%2816%2900020-8/pdf Abstract and Poster: https://www.eventscribe.com/2016/posters/ISETCIO/SplitViewer.asp?PID=MjYyNjA1MDAyNQ

26. Heithaus RE, Onofrio A, Weir V, Rees CR. Can aprons be properly evaluated for their protective quality without in-house validation? Poster at the International Symposium on Endovascular Therapy (ISET) 2016, February 6-10, Hollywood Florida. Abstract: J Vasc Interv Radiol 2016;27:e1-e21, page e11. http://www.jvir.org/article/S1051-0443%2816%2900020-8/pdf Abstract and Poster: https://www.eventscribe.com/2016/posters/ISETCIO/SplitViewer.asp?PID=MjYyNjg3MDAwOQ

27. 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 Sept;32(3):129-139. doi: 10.1088/0952-4746/32/3/N129.

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30. http://www.infabcorp.com/is-your-lead-apron-protecting-you/ Access date 2-23-2016

 

APPENDIX B (Interesting excerpts from other publications):

“Therefore, under the experimental conditions described above, for an average weight reduction of 28% the lead free aprons allow on the average a 73% increase in transmission at 70 kVp and a 31% increase in transmission at 100 kVp when compared with the lead-containing 0.5 mm lead equivalent aprons.” (4)

“The manufacturers should be required to standardize their methods of transmission measurement and devise methods to minimize batch-to-batch variability…manufacturers should also be required to present transmission curves at a range of kVp values in their product literature. Enforcement of the lead equivalent requirement or specification might fall under the auspices of the FDA or some other federal government agency.” (4)

“Of note, 18.5% of the respondents self-reported occasional failure to wear personal radiation badges, and an additional 28.6% reported never wearing radiation badges. This practice was most prevalent in those aged 51–60 years, in whom 41.4% reported not wearing radiation badges at times and 39.5% routinely failed to wear badges (Fig. 1).” (24)

“In 2006, Americans were exposed to more than seven times as much medical ionizing radiation as was the case in the early 1980s, and the amount due to interventional fluoroscopy increased 33 fold.” (National Council on Radiation Protection & Measurements (Bethesda. MD). Ionizing radiation exposure of the population of the United States. Report No.:160. Available from: http://www.ncrponline.org/PDFs/2012/DAS_DDM2_Athens_4-2012.pdf ) (Smith-Bindman R, Miglioretti DL, Johnson E, Lee C, Feigelson HS, Flynn M, Greenlee RT, Kruger RL, Hornbrook MC, Roblin D, Solberg LI, Vanneman N, Weinmann S, Williams AE. Use of diagnostic imaging studies and associated radiation exposure for patients enrolled in large integrated health care systems, 1996–2010. JAMA 2012 Jun 13. Available from: http://jama.jamanetwork.com/article.aspx?articleid=1182858&resultClick=3 )

“Almost every manufacturer makes the claim that their aprons are “the lightest on the market”. While there are miniscule differences in the weights of the powders used to produce radiation protection materials, the simple truth of the matter is, there are no secret formulas and almost all apron manufacturers use variations of the same metals in their products. The bottom line here is, if it’s lighter weight, it is not offering the same protection levels. Plus or minus a very small percentage, a true .50mm LE apron is going to weigh the same from one manufacturer to the next.” (30) Access date 2-23-2016