Two studies presented at The International Symposium on Endovascular Therapy (6–10 February 2016, Hollywood, USA) found that there was inadequate information from manufacturers about many of their protective garments. This means that informed decisions are hard to make regarding the radiation protection offered by these garments.
One study recommended in-house testing because no manufacturer or vendor provided enough useful information to properly evaluate protection for all of their products. Another used a wooden phantom wearing the protective garment in place of the interventionist in a clinically realistic set-up to identify non-lead garments as especially poor protectors, even when they are not particularly lightweight.
A presentation from Robert Evans Heithaus, Radiology, Baylor University Medical Center, Dallas, USA and colleagues set out to survey the publicly available information for many aprons to determine if their protective capabilities can be adequately evaluated by prospective users without in-house experimental validation.
As a background to the study, the researchers noted: “Previous studies have shown that the protective capacities of many garments are not clearly and accurately represented by their labels. Non-lead materials have been shown to have highly energy-dependent attenuation and, therefore, are poorly represented by specifications at one or two beam qualities. In addition, non-lead materials also require broad-beam measurement geometry to avoid overestimation of protection due to the presence of fluorescent radiation.” They further noted that in some cases, labelled lead equivalences often relate only to overlap zones of vests and skirts, but that this is not often explicitly disclosed by manufacturers on their labels or websites.
Evans Heithaus and colleagues reviewed publicly available information for 17 manufacturers of aprons and seven vendors for information such as broad-beam testing for non-lead products, multiple energies tested for non-lead products, ≥ one energy tested for lead products, clarity on overlap zone protection, and material density information.
The investigators found that no manufacturer or vendor provided enough useful information to properly evaluate protection provided for all of their products. None provided enough information to evaluate protection relative to weight, which would be useful for users when choosing a protective garment. The investigators deemed lead-containing garments evaluable for protection if lead equivalence was tested at one or more energy levels and if it was clearly stated whether specifications refer only to overlap zones. Non-lead aprons were deemed evaluable if they included testing at four or more energy levels with broad-beam geometry and when there was clarity regarding overlap zones.
“Based on current labelling conventions and practices, garments cannot be adequately evaluated for protection or protection relative to weight by our study criteria. Careful in-house experimental validation is highly recommended to prevent higher than expected radiation exposures that may go unnoticed with many models,” Evans Heithaus Jr told delegates.
A second study, presented by Andrew Lichliter, reported on a testing method that was used to provide realistic comparisons of protective capabilities of different garments in a set-up resembling an actual interventionist in a procedure. Using different methods than previous tests of aprons which also showed high variation for similarly labelled aprons, their method can help to compensate for labelling deficiencies and inconsistencies, energy dependency of non-lead, garment geometry, and weight, they noted.
The investigators carried out a clinical evaluation of protective garments with respect to garment characteristics and manufacturer label information.
“The inadequacies of product testing and labelling information of aprons and skirts/vests are well reported, especially for non-lead and lightweight models. Manufacturers perform tests in settings that are not realistic to clinical use, and the energy dependence of non-lead can affect performance at energies in a clinical setting,” they wrote.
Lichliter and colleagues tested operator exposures inside garments in a clinically realistic set-up with clinically appropriate energy settings and examined trends related to weight, configuration and composition. They tested sixteen models of garments containing lead or non-lead, and a zero gravity device (Zero-Gravity, CFI Medical) for operator exposure (mR/h) from X-rays scattered from an acrylic patient phantom in an interventional suite. The operator phantom was a wooden frame supporting the garments in the same configurations as a real operator standing in a typical working position and containing a dosimeter on its mock torso. The garments were also weighed.
The researchers found that the variability of exposures was high (standard deviation = 0.44), especially for the non-lead garments, which comprised nearly all of the especially poor protectors, even when not particularly lightweight. Protection correlated very strongly with the weight of the garments, highlighting the deficiencies of the lightweight models. They further found that apron configurations were lighter than skirts/vests on average (3.3 vs. 4Kg, respectively) with similar mean exposures (0.55mR/h for both) except for three particularly heavy and protective skirts/vests, one of which was non-lead. The non-lead models were not more protective per weight overall. Of the four with the highest protection per weight, two were lead and all were aprons. Zero-Gravity (1mm lead) provided the lowest exposures (0.06 mR/h, or 9.8% of the mean for all other garments). For those labelled 0.5mm lead equivalent, exposures ranged widely from 1.59 to 0.13, with far higher variability for non-lead (SD = 0.47 vs 0.28 for lead).
“The test method provided realistic comparisons of protective capabilities of different garment, which could help a user choose between purchase options, compensating for labelling deficiencies and inconsistencies, energy dependency of non-lead, garment geometry and weight. The non-lead garments did not show better attenuation/weight. The findings described, including a 12-fold difference of exposures for models labelled 0.5mm lead, highlight the necessity for such internal validation for interventionists, especially for non-lead models,” the researchers wrote.
Chet Rees, clinical professor at Baylor Scott and White Health, and one of the co-authors of the study, pointed out that the problems of accurately representing the attenuating capabilities of aprons in their labels stems from a complex set of physics principles which were originally intended for lead garments, but do not work as well for the non-leads which are burgeoning in the market, as well as some laxity of regulation and slow change in testing standards. This means that the manufacturers are often in compliance, despite the findings described.
“Our hopes are to raise user awareness so that users become more demanding of the manufacturers to provide more information than required by law so that they always know what they are getting and can more intelligently compare models. In the meantime, the simplest piece of advice we can offer is to stick with non-lightweight aprons that contain some lead in them and do not rely on overlap for their full labelled lead equivalency, because studies including ours have shown these to perform well,” Rees said.
Rees has a blog that provides a comprehensive FAQ-style overview on the issue of light weight aprons.