The ins and outs of radiation shielding

October 17, 2022
by Lauren Dubinsky, Senior Reporter
Lead is the go-to material for radiation shielding for a reason. It’s high-density, low-cost and has excellent attenuation. The downside is that this material can lead to significant health problems if it’s ingested or inhaled.

Although there is no dispute that lead is toxic, studies investigating the effect of lead exposure on radiology personnel have produced conflicting findings. A study published last year in the Archives of Environmental & Occupational Health collected hand dust wipe and blood samples from 58 radiology department workers in an academic hospital.

The research team did not find an elevated risk of lead contamination on the study participants’ hands or in their blood. They concluded that although the sample size was small, lead poisoning is “unlikely to occur with high frequency in lead shield users.”

Another study from last year revealed that radiographers working in radiological departments in general hospitals had significantly higher concentrations of lead in their scalp hair than administrative staff. The study, which was published in Nature Research, also found that the mean lead concentration in their hair was comparable with that of workers in lead-related manufacturing plants.

Lead alternatives made of tungsten and bismuth were developed in an attempt to avoid those risks. But those products come with higher price tags and that has hampered their growth in the market.

"The problem with the company that was making this non-lead-based shielding material is they can never get down to the price point,” said Adam Evearitt, co-owner of Atom Physics. “There are very few people that, when push comes to shove, aren't aren't going to make decisions based on price."

In July, a research team based in Egypt announced that it developed a 3D-printing technique for creating light bismuth radiation shielding material. The material is made up of micro and nano bismuth particles between layers of polylactic acid thermoplastic polymer.

“The challenge with bismuth is that it is much more expensive than lead and the lower-density factor requires thicker shielding,” said Kevin Milne, president and CEO of MarShield. “In most cases up to five times the thickness of lead is required to achieve the same shielding.”

MarShield offers a non-lead shielding product called FlexShield XYZ, which is polymer-based and can be made into thin materials to replace sheet lead. It comes in different formulations including tungsten, bismuth or iron, but tungsten is what is mostly in demand.

The research team at Alexandria University claimed that the low-density nano bismuth particles have a better mass attenuation coefficient than bulk bismuth, and the result is a lighter and more effective radiation shielding material.

A benefit of this new 3D-printing method is that it allows the user to create shields of the right shape and dimension for any application. Milne explained that customers are more interested in this level of customization.

“We find that clients all have very specific needs and requirements,” said Milne. “Going to a catalog and ordering off page number 203 is not suitable in most cases.”

It’s now a standard practice for MarShield to customize any of the products they manufacture, including L-blocks, rolling barriers, and custom lead-lined cabinets. Due to recent supply chain issues, they also offer stock base lead cabinets, rolling barriers and other products, but customization can be added where needed.

Although Milne does see a place for lead alternatives in certain circumstances, lead shielding is still his company’s bread and butter. He estimated that it’s used in 99% of their shielding products.

“Pure lead provides the most effective shielding,” he said. “High density and layering allow for high gamma attenuation coefficients and achieve high attenuation ratings relative to other shielding materials.”

He added that lead can be cast, custom-machined, rolled into sheets and impregnated into clear vision glass and acrylic. It can even be coated if a customer is concerned about exposure and can be recycled.

The importance of a physicist
Aside from the shielding material you plan to use, many things need to be taken into consideration when you embark on a new radiation shielding project. According to Bryan Bordeman, operations manager at Global Partners in Shielding Inc., the first thing you should do is ensure you have a physicist on board.

“One of the biggest mistakes is that the customer gets so far down the line before consulting somebody that is familiar with the different modalities and they have to undo things that they did already,” he said.

On one of his recent projects, the customer originally enlisted a group of people in the design phase who gave them inaccurate advice. They wanted to have the room on the first floor of their new two-story building, but Bordeman came onto the scene and found that the ceiling height was too low.

The ground floor is the ideal location since there is only dirt underneath. Because of the low ceiling height, the room had to be moved to a higher floor and shielding needed to be installed in the floor.

“When they put them on the second or third stories, you have to shield the floor,” said Bordeman. “It’s not impossible, but it's very tricky because it raises the floor up. Then it is higher than all the rest of the floors and they have to put in ramps.”

The physicist can also tell you the ideal location of the CT or X-ray unit within the room. Evearitt can look at the floor plan and recommend the best orientation of the equipment to save on shielding costs.

"Sometimes it makes a big difference where you put the X-ray machine within the room,” he said. “The occupancy on the other side of the wall really matters.”

He explained that the best spot is in the corner of the building so that at least two of the walls are exterior walls. The less occupancy on the other side of the room, the less shielding that’s required.

For shielding guidance, he follows the National Council on Radiation Protection and Measurements (NCRP) 147 for medical X-ray facilities and NCRP 151 for radiation therapy centers. It provides a table that lists the different occupancies for the different types of rooms there are.

If there is an office or a neighboring business on the other side, Evearitt said that he has to assume there will be 100% occupancy. If it’s a hallway, 20% of the time someone may be walking past the wall when a patient is being scanned.

"Board-certified physicists have access to these reports and they're always going to refer back to that,” said Evearitt. “That's your ammunition if somebody sues for radiation exposure. You can point to that document and say you followed this nationally-recognized guidance document."

Know your anticipated workload
You will need to provide the physicist with your anticipated workload so they can accurately determine how much shielding is needed. If you give them an inaccurate number, you’ll be doing yourself a disservice.

A third-party X-ray vendor asked Evearitt to do a shielding report for a machine they sold to a veterinary clinic. When asked about the X-ray’s workload, he noticed they had a tendency to underestimate the amount in order to save the doctor money.

"They want to save the doctor money by not having the expense of all the shielding because they're trying to make the sale,” he said. “They're going to give me a really low workload because they know that's going to result in little or no shielding."

If the workload amount that he’s given seems too low, Evearitt will investigate to determine the accurate amount.

A facility can run into problems with the shield if the workload grows. They might have only done 50 X-rays per week when they first opened, but if they add onto the office and hire more doctors, they may then be doing 100 X-rays per week.

That would double the radiation dose hitting the walls, which means the shielding would no longer be effective. It can be an easy thing to avoid because the business owner likely won’t want to pay for another report and the cost of potentially adding more shielding.

Lastly, a facility could change how a room is used. For instance, the X-ray room could initially be next to a storage room, but if they eventually remodel and change it into an employee lounge, the shield won’t be effective anymore.

In Colorado, where Atom Physics is located, an inspector is required to visit a site annually to view the shielding design. If there was a remodel, that’s when the inspector would find out about it.

Remodeling that takes place within the CT or X-ray room can also damage the integrity of the shield. The shield will be fine if a nail is hammered into the wall and stays there, but problems arise if the nail is removed.

Even if you use putty to seal the hole in the drywall, there will still be a hole in the shield. Evearitt stressed that if you are doing any type of remodeling, someone needs to oversee the shielding portion.

"Like any kind of remodeling work or anything that's done to a room, you should have the shielding reevaluated,” he added. “That can include putting a new furnace in, redoing the duct work or electrical things like cutting out and putting outlets in the wall."

Have a clear delivery plan
MarShield’s Milne wished customers were better prepared for the delivery of the shielding products. Lead is very heavy at 700 pounds per cubic foot and getting it to an upper floor can be difficult if there isn’t a clear plan.

“Accessibility plays a big part in planning and receiving the shielding products as some facilities are multiple levels and that can be challenging,” he said. “Pre-planning with the contractor and/or the facility goes a long way to provide a seamless delivery and installation process.”

This is especially a concern when shielding a radiation therapy room. There needs to be a clear delivery plan for the heavy cementitious-based shielding materials, linear accelerators and other equipment.

“If the installation of these items is slated for a level with a basement below, there needs to be consideration of this delivery route,” said Robert J. Farrell, CEO of Veritas Medical Solutions. “The delivery floor may need to be supported from below along the delivery path, or an alternate route may need to be considered, given the weights involved.”

For a new construction site, a crane can be used to deliver the shielding materials to the right floor. If it’s an existing building and the radiation therapy room is planned for a third or fourth floor, there will usually be access to a freight elevator.

For one project, Veritas had to make the shielding material into half-palettes, so a construction service elevator could lift it to an upper floor.

Trends in radiation therapy shielding
Farrell often finds that clients don’t know what equipment they plan to purchase in the initial phase of a project. What they do know is that they want the best treatment equipment for their patients as technology advances.

“The facility often wants to ‘future proof’ their design for future innovations in treatment equipment,” said Farrell. “While this is a valiant exercise, the differences in treatment machine types and modalities offered makes the coordination with other trades that much more of a critical point. Without the proper coordination, mistakes can be made, costing aggravation, time and money.”

Another aspect he wished facilities were better prepared for is the placement of the required structural foundations. When Veritas performs its preinstallation inspection at a customer site, there have been times the foundations were not placed properly according to the isocenter location.

Historically, many facilities put these rooms in the basement. That approach saves on shielding costs because in a subterranean environment the earth can be used as a shielding material.

However, the trend is now to have the radiation therapy room on the ground floor. It eliminates the hassle of a patient having to use elevators or stairs to get to their treatment appointment.

“We believe that the primary focus should be the patient,” said Farrell. “With the patient in mind, facilities often desire to keep the radiotherapy department at the ground floor level. This permits the patient to experience natural light, which can be very beneficial to the patient.”