Weighing In On Personal Radiation Protection

This article is the first of a series to be published over the next few issues of Spectrum that will focus on the lead aprons used by staff in diagnostic imaging and interventional procedures, and the factors that have contributed to the situation mentioned above. The intention of these articles is to provide interested readers an insight into what aprons are made of, how they work, what the metrics of protection are and how they are measured, and most importantly, how to interpret the marketing information provided by manufacturers and suppliers engaged in the business of selling aprons. People required to make lead apron purchasing decisions will hopefully find these articles helpful, as will anyone who is curious as to why two aprons of the same size and with the same claimed level of protection can weigh substantially different amounts.

Weight vs Protection

Naturally there is a demand from the market for lightweight protective garments because weight is a very significant contributor to overall comfort. Modern medical practices often involve complex and long procedures, requiring aprons to be worn for extended periods of time, and fatigue or injury are very real issues for wearers.

Unfortunately, it is unavoidable that adequate attenuation of diagnostic x-ray radiation requires a significant mass of material and so protection, and wearing comfort are somewhat in competition with each other. A compromise needs to be made whereby an adequate level of protection is provided, and the wearer afforded good quality of working life.

Apron manufacturers have responded to this challenge in the last several decades by producing aprons that use materials other than lead as their key attenuating agent. The accepted testing laboratory measurement methods available to determine the attenuating ability of aprons have not been truly representative of actual exposure situations for wearers though. As a result, the market is full of non-lead or reduced-lead aprons with weights significantly less than the weight of the equivalently labeled lead based garment. Often, these claims are quite inaccurate in terms of actual protection.

This is not to say that manufacturers are deliberately misleading their customers. Rather, a shortcoming in testing methods has existed that has provided the so-called lightweight non-lead garments an apparent advantage. The situation has begun to change with the recent publication of new measurement methods for testing laboratories to follow. These methods give more representative measures of the attenuating ability of a nonlead apron when compared to a lead apron, and so a more accurate picture is beginning to emerge. A consequence of these changes will not necessarily be that apron weights will increase. Instead, it is hoped that the labelling fixed to aprons to indicate their protective abilities will be a more accurate reflection of reality. Unfortunately, it takes some time for new standards and methods to be adopted, and in the meantime, manufacturers will continue to seek an “edge” by making statements based on results obtained using the older standards.

Evolution of the Apron

As mentioned, the lead apron has evolved considerably in the last century. Regardless of the construction particulars, all aprons rely on the same radiation interaction mechanisms to achieve their attenuating abilities, and these mechanisms require the use of high atomic number elements.

Conventional textiles used for garment manufacture do not contain high atomic number elements, and so some means is required to incorporate these elements into suitably flexible and workable substrate materials.

Historically, the substrate material used was rubber, and lead has been the preferred attenuating element because it has a high atomic number, exists as a stable pure metal, and does not react with other materials. It can be readily powdered to a fine particle size, and in this form can be mixed into the uncured rubber. Once cured, a flexible sheet of attenuating core material is obtained that can be cut into patterns and stitched into garments. Early aprons materials were not particularly flexible, and styles were limited to “front and back over-the-shoulder drapes”. More recently synthetic rubbers, and PVC vinyls have been employed, and these materials can be cast into thinner layers, affording more flexibility. This has allowed for the option to manufacture actual fitted vests with companion skirts as a means of providing full protection to the human trunk, but with the advantage that weight is distributed to the shoulders and the hips.