A shielded MRI door
(image courtesy of ETS-Lindgren).

Lead use in medical shielding: pros, cons and alternative materials

November 13, 2012
by Diana Bradley, Staff Writer
The primary purpose of medical shielding is to do just that -- shield and protect hospital patients, visitors and staff from hazardous equipment and devices that produce X-rays and gamma rays. But one of the most popular high-density shielding materials is ironically a toxin itself: Lead.

Ranked number two on the Agency for Toxic Substances and Disease Registry’s 2011 Substance Priority List, lead poses a bigger risk to human health than mercury, methane and asbestos, along with a slew of lesser-known chemicals. Because of health concerns, lead from gasoline, paints and ceramic products, caulking, and pipe solder has been dramatically reduced in recent years, according to the ATSDR website. Even so, it is still widely used in medical shielding.

“Lead shielding has been in use throughout my 36-year tenure in Nuclear medicine,” says Don Bogutski, president of Diagnostix Plus Inc., a supplier of new and refurbished nuclear medicine equipment and services.

While concrete is commonly used for radiation containment, if space is limited, or a retrofit is needed, lead is the go-to material, according to Chris Lewis, NELCO’s manager of design and engineering. For example, when applying shielding to a treatment room door, the door can be much smaller in size if lead is utilized.

“Essentially, one inch of lead is equivalent to six inches of concrete, so you can literally reduce the amount of material required to achieve the same thing,” Lewis explains.

NELCO provides shielding for the proton marketplace, radiation oncology, diagnostics for imaging and MRI shielding. The company continues to use lead in combination with other materials for radiation shielding.

But lead isn’t used in all medical shielding. For example, it is not an ideal material for RF shielding vendors, notes Benjamin Turner, VP of Global Business Development for ETS-Lindgren (ETS-L), an RF shielding manufacturer. But even there, exceptions exist.

“With the advent of multi-modality equipment (PET/MR, PET/CT) you may have a situation where you need to combine radiation shielding materials with RF shielding materials, but for the most part, this is done by two separate vendors,” he says.

On the other hand, for those vendors that regularly use lead, the substance has recently become a target for limited and safer use.

“Many companies around the world are trying to eliminate lead from their product,” says Joe Sery, CEO, Tungsten Heavy Powder, Inc., a tungsten powder manufacturer. “They just feel lead is too toxic.”

Worldwide legislation
There is a strong movement against the use of lead coming out of Europe with the Restriction of Hazardous Substances directive, which was adopted by the European Union in 2003 and took effect in 2006. The initiative restricts the utilization of six hazardous materials in manufacturing processes: lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ether. However, in the medical equipment industry there has been an exemption, which will run through the end of 2013, notes Russ Wolff, business development manager, Thogus Products, a custom injection molder.
“From what I understand right now, primary shielding can still be a lead-based material, even beyond the end of 2013,” explains Wolff. “But secondary shielding will need to be converted over to a lead alternative.”

For example, if there is an X-ray machine that has a collimator that focuses the X-ray beam, lead-based material could continue to be utilized, as it falls directly in the line of radiation. On the other hand, if there were housing encasing the Xray tube, to shield against scatter or bounce back, an alternative material would need to be used.

Meanwhile, the U.S. continues to use lead across the nation in a multitude of products. Sery speculates, though, that the U.S. is about five years behind Europe in terms of lead exemption. Currently, the U.S. Environmental
Protection Agency and the Occupational Safety and Health Administration are eyeballing companies that perform various processes involving the fabrication, machining and casting of lead to ascertain they are managing it as carefully as possible.

“When you’ve got a toxic substance such as lead, it is very difficult to handle it in a safe manner,” says Wolff. “We’ve got a number of our customers that not only want an alternative because of the direction coming out of
Europe, but with the EPA and OSHA restrictions in this country, they want to get away from lead.” But the real wall here is the International Lead Association’s strong lobby, resulting in very few lead-replacement legislations, says Sery.

“When the U.S. government tackled the toxic substance asbestos, they did it very aggressively and that’s what they need to do with lead,” he says.

Bit by bit, however, lead’s use may be waning for some. Among other projects, Samsung in South Korea recently contacted Thogus about developing a green, RoHS-compliant collimator for their CT machine. Additionally, China is intending to echo the EU directive with its own RoHS, entitled, “Management Methods for Controlling Pollution Caused by Electronic Information Products Regulation.”

Safety concerns
Companies that still utilize lead in shielding must have safety precautions in place. If not handled carefully or contained properly within wall structures, it can be an environmental hazard. This is especially true when being stored outdoors in an unprotected space where the materials are exposed to the elements and could potentially leach into the soils and ground water, according to David Farrell, CEO and president of Veritas Medical Solutions, a company that specializes in radiation shielding in medical and industrial settings.

Proper training is the primary way to protect workers handling lead materials. Unsafe handling – for example, not wearing gloves —can lead workmen to ingest the toxin, picking up lead oxides.

“If [workers] then handle food prior to washing their hands, or in other ways allow the oxide contaminates to enter the body, elevated levels of lead can be found in the individuals,” Farrell explains. “Another common example includes workers momentarily placing their cigarettes on a piece of lead, picking them up, and inhaling.”

In many cases, when lead-based medical shielding is installed in a larger hospital, a construction manager may run the project, and they will have their own health and safety program. But to ease any worries about lead, companies like NELCO have implemented their own strict program.

“If we are cutting lead in the field, a cutting booth contains the lead, and an air filtration system is on site so no one in the area can breathe in toxins,” says NELCO’s Lewis. “The individual working on that lead is also required to wear an appropriate respirator so their exposure is limited.”

From a physics perspective, lead shielding also has problems when used in high-energy X-ray shielding, notes Steven Johnston, director of physics at Veritas. In those cases, the high-energy X-rays or photons can cause the lead to become a source of neutron radiation, which further needs to be appropriately shielded by something else. In fact, most of the neutrons produced in the treatment room are produced in the head of the accelerator where the photons are interacting with the lead casing and the other high Z materials surrounding the linac head.

“Lead is a terrible shielding material for attenuating neutrons,” says Farrell. “While photons are effectively attenuated with very dense materials such as lead or steel, neutrons [from medical linear accelerators] are generally moderated [slowed] with hydrogenous materials, and captured with the introduction of materials with a high neutron cross section such as boron, lithium or cadmium.”

Lead alternatives: Industry eyes tungsten
Although it is possible for lead to be safely handled and utilized in shielding applications, the associated risks are spurring some medical shielding manufacturers to hunt for lead-replacement materials. There are some considerations that generally weigh in favor of alternatives to traditional solutions, such as specialty thermoplastic resins and other metals.

A tungsten shield (image
courtesy of Tungsten Heavy Powder)

“A very popular replacement at the moment is tungsten, which can stop all types of radiation,” says Tungsten Heavy Powder’s Sery. A grayish-white, lustrous metal, tungsten is one of the densest naturally occurring elements, with its name derived from the Swedish word “tung-sten” meaning “heavy stone.” Its primary deposits are found in the European Alps, the Himalayas and the Pacific Rim.

“Tungsten-filled polymers block radiation at the same rates as lead and provide radiation shielding and attenuation up to, and including, a one-to-one equivalency to lead,” says Thogus’s Wolff.

Typically, tungsten is used in radiation, nuclear, PET and SPECT shielding. But manufacturing a plastic material resistant to EMF and RF can be challenging. To accomplish this, Thogus adds a carbon or stainless steel fiber filler to the plastic compound to achieve some form of static dissipation.

Additionally, while lead is supple, tungsten is brittle, making it much more difficult to work with and shape. The production rejection rates are higher as is breakage with tungsten, Bogutski notes. To get over this hurdle, Tungsten Heavy Powder has a unique process. The company uses a high-density tungsten powder, as opposed to regular tungsten powder. Instead of mixing the powder together to pour into the cavity, Sery creates the component – which is a mixture of high-density powder and epoxy – by packing the powder in a mold and vacuuming the polyurethane into that compaction. It is then cured in a furnace, resulting in tungsten that resembles a high-density solid block.

An unfinished tungsten collimator
with mold (image courtesy
of Tungsten Heavy Powder)

“High-density tungsten powder has a certain morphology to it,” says Sery. “The shape of the particle is unique and conducive to the higher density when packed into a volume or space.”

Bottom dollar: Lead wins when money is thrown into the equation
Although tungsten is commonly used in nuclear medicine and is acceptable from a physics perspective, its usage is still just a fraction of lead’s, says Bogutski. There are three reasons for this: cost, availability and material versatility.

For example, Biodex, which has been producing nuclear medicine shielding since 1949, uses solid tungsten and machines it into necessary shapes for effective syringe shielding for nuclear medicine. However, there are still some cases where lead is more appropriate than tungsten.

“With larger shields – like large PET shielding -- Biodex still uses lead due to cost,” says Robert Ranieri, Biodex’s VP of sales. “But we use lead encased in steel or stainless steel.” Typically, the cost of lead is $1.50 to $2 per pound, while tungsten materials and plastic compounds can run upward of $50 per pound. “Often, in a nuclear medicine setting, thousands of pounds will be required,” says Bogutski. “The dollar difference adds up quickly.”

Unfortunately, the cost of tungsten has continued to rise in recent years. This increase is due largely to the fact that 70 to 85 percent of the world’s tungsten is imported from China, according to Sery. However, this may soon change.

“There are a number of companies opening up tungsten mines in the United States as well as in Canada to offset some of the high costs coming out of the Far East,” Wolff says. “But for the time being, if medical companies can get by with lead, they are certainly going to do that because it’s less expensive than any of our compounds.”

However, companies like Thogus have developed methods to get over this economic hurdle.

“If you have a part that’s traditionally been made out of lead and it has a lot of secondary operations -- let’s say it needs to be machined, coated, painted or protected from anybody touching it -- more often than not, we can come up with an economic justification for our materials, because we eliminate secondary operations by injection molding a part,” says Wolff.

In addition, lead has a single specific gravity – 11 grams per cubic centimeter. The advantage of using a material like tungsten is that the density can be custom compounded for a specific application.

“We can tailor make the mixture; we have lower densities that are available all the way down to 2.7 grams per cubic centimeter, which gives us the opportunity to customize for the application,” says Wolff.

As density is reduced, so is the amount of tungsten filler. The result: lower costs.

“The beauty of tungsten is you don’t need expensive molds,” explains Sery.

The bottom line for lead
Although lead exemption may be on the industry’s to-do list, it doesn’t rank high on it. In fact, some experts believe lead utilization in medical shielding may increase in certain areas.

“We would expect to see a growth in the use of cancer treatment centers involving high levels of lead shielding,” says Robert Wardley, chairman of Wardray Premise Ltd. So the wait will continue to see where lead’s path leads.

DOTmed Registered Shielding - everything Companies

Names in boldface are Premium Listings.
Robert Rumney, MRI Corporation, CA
Lou Campedelli, NELCO, MA
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Vishnu Srivastava, International Medical Associates Ltd, OH
Glen Watkins, ETS-Lindgren, TX

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Haitham Khoury, MEDMACK, United Arab Emirates
Horacio Jose Gomez, VCG Imagen SRL, Argentina
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Chand Jain, Komega Impex P. Ltd., India
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