Radioprotective Garments: A Medical Physicist’s Perspective

If you read our previous blog post on ALARA, you learned that the ALARA standard used worldwide for managing dose to radiation workers actually stems from the Linear-No-Threshold (LNT) dose-response model. If the LNT model is correct, risk of deleterious effects like cancer increases linearly with radiation dose, and there is no safe amount of radiation exposure where the increased risk is zero. Because LNT suggests that there is no safe radiation dose, this motivates us to keep both our radiation dose, and the radiation dose that our patients receive very low. One of the most important ways that we, as radiation workers, accomplish ALARA is through the use of radioprotective garments. In this article from FluoroSafety and Universal Medical, several aspects of radioprotective garments will be discussed.

Radioprotective Garments

Today, radioprotective garments come in all shapes and sizes and are made from many different materials. In fact, the use of “lead aprons” to describe these garments is not quite correct, as many garments currently on the market contain no lead. Many different types of garments are used individually or in concert to protect radiation workers, including aprons, thyroid collars, vests, kilts, and protective eyewear. Let’s take a closer look at the difference between lead and lead-alternative protective garments.

Lead Protective Garments

The conventional lead apron is actually made from more than just lead; it is lead powder permanently bonded in a thick rubber or vinyl matrix allowing the apron to be flexible, comfortable, and long-lasting.  The rubber matrix is further protected by a thin vinyl covering which facilitates cleaning, while nylon straps with either Velcro or compression buckles secure it to the wearer. The protection provided by a lead garment may be quoted simply as “0.50-mm lead” or as “0.50-mm lead-equivalent”. These descriptions are interchangeable for lead garments.

A typical 0.50-mm lead apron will transmit approximately 2% of a scattered fluoroscopic X-ray beam.

Lead-Alternative Protective Garments

The product lines of most vendors now include lead-alternative radioprotective garments. Such garments may be lead-free or lead-composite. Lead-free garments use metals such as tungsten, tin, antimony, and bismuth in place of lead, while lead-alternative garments still incorporate some lead along with these other metals. The construction of lead-alternative garments is nearly identical to that of lead garments, except that metal powders other than lead are included in the rubber matrix that comprises the protective layer of the garment.

Advantages of Lead-Free Garments

Lead-free garments have two advantages over lead garments. First, lead-free garments are environmentally friendly and non-hazardous. Hospitals that replace a large number of protective garments each year may see a small cost savings because disposal of worn out lead-free garments can be handled through a conventional waste stream, while lead or lead-composite garments must be handled as hazardous waste. The second potential advantage of lead-free garments is the possibility that, by optimizing the mix of metals used in the garment, a garment that has the same performance as lead, while being lighter weight, may result. This is possible because the alternative metals used have strong absorption k-edges that closely match the energies of scattered fluoroscopic X-rays. Over a narrow range of energies, these metals attenuate radiation as well as or better than lead while being less dense, and therefore lower weight than lead. Manufacturers of such garments often advertise them as being “lighter than lead” while providing the same protection.

Determining Lead Equivalence

These are difficult claims to evaluate. Because lead-free garments do not use lead, determining the lead equivalence of such a garment is an extremely challenging problem. Recall from the last paragraph that the alternative metals absorb radiation as efficiently as lead only over a very narrow range of energies. This is one reason that a number of different metals are used, to spread this range out as much as possible. This also means that transmission of a lead-free garment depends very strongly on X-ray energy¹. Therefore, the specification of the “lead-equivalence” of such a garment at a single X-ray energy is not a complete characterization of its protective value.

Radioprotective garments typically provide the full rated protection at the front of the garment. Aprons have a single full-thickness layer while a skirt will overlap to provide the full rated thickness in the front. Most garments provide less than the full rated protection at the back (e.g., 0.25-mm), as most medical radiation workers face the source of radiation. This is an important consideration for fellows or other radiation workers who spend large amounts of time with their back facing the patient – such workers may consider purchasing a garment with at least 0.35-mm protection in the back.

Until recently, many state regulations required that personnel working around fluoroscopes wear protective garments of at least 0.50-mm lead equivalence. However, recently the National Council on Radiation Protection and Measurements, considering the tradeoff between orthopedic strain and radiation protection, suggested that 0.35 mm lead-equivalent garments are sufficient for most medical radiation workers², and state regulations are being updated to reflect this new guidance. While a typical 0.50-mm lead apron transmits approximately 2% of a typical scattered fluoroscopic X-ray beam, a 0.35-mm lead apron transmits approximately 5%. For comparison, the transmission of 0.50-mm lead-free protective garments typically ranges from 4-6%.

Lead or Lead-Free?

If you are considering changing from a lead to a lead-free garment, or from a nominal 0.50-mm garment to a nominal 0.35-mm garment, the best way to proceed is to ask your radiation safety officer or medical physicist to switch you to an EDE1 radiation monitor wear method. Using the EDE1 wear method, you will be supplied with 2 dosimeters, one worn at the collar level outside your protective garment and one at the waist level under your protective garment. This wear method allows a direct evaluation of the protective value of your new garment for your specific work environment. More details on the EDE1 wear method are available in the Advanced Training Program from FluoroSafety.

A word on weight

While it is possible that lead-free or lead-alternative garments can provide adequate protection at a reduced weight, the most important garment parameter relating to operator comfort is how well it fits. For individuals who wear protective garments every day, a custom fitted vest and kilt combination garment will result in the least orthopedic strain. After due consideration is given to the fit of the garment, the required protective value and weight of different garment options can be considered.

About The Authors:

A. Kyle Jones, PhD and Alexander S. Pasciak, PhD

Founders, Fluoroscopic Safety, LLC

Dr. Kyle Jones earned his B.S. in physics from Furman University and his M.S. and Ph.D. in medical physics from the University of Florida. Dr. Jones is currently employed as a Diagnostic Medical Physicist and Assistant Professor at MD Anderson Cancer Center.

Dr. Jones is board certified in Diagnostic Medical Physics by the American Board of Radiology, is a Licensed Medical Physicist in the state of Texas, and is MQSA qualified. Dr. Jones is active in multiple research endeavors in the fields of radiation safety and diagnostic medical physics, is widely published in high impact journals, and is actively involved in teaching and training medical physics graduate students, medical physics residents, and interventional radiology fellows.

Dr. Alexander Pasciak earned his B.S. in electrical engineering from the University of Washington and his M.Sc. in health physics and Ph.D. in nuclear engineering from Texas A&M University. Dr. Pasciak completed a two-year diagnostic medical physics residency program at MD Anderson Cancer Center in 2009.  For the past five years, Dr. Pasciak has worked as Diagnostic Medical Physicist at the University of Tennessee in Knoxville where he carries the rank of Associate Professor of Radiology.

Sources:

1. A.K. Jones, L.K. Wagner, “On the (f)utility of measuring the lead equivalence of protective garments,” Med Phys 40, 063902 (2013).

//www.ncbi.nlm.nih.gov/pubmed/23718618

2. National Council on Radiation Protection and Measurements, Radiation dose management for fluoroscopically-guided interventional medical procedures. NCRP Report 168, (NCRP, Bethesda, MD, 2011).

//www.ncrponline.org/Publications/Press_Releases/168press.html