Considerations before a radiation shielding project
October 11, 2021
by Lauren Dubinsky
, Senior Reporter
Regulatory requirements for X-ray radiation shielding can vary significantly from state to state. This can make it challenging for shielding equipment vendors and providers to determine exactly what needs to be done for every project.
There is no central document that lists every state’s requirements, but Adam Evearitt, co-owner of Atom Physics, has put together his own personal one from years of experience in the field. He is registered in all 50 states and estimates that he does roughly 100 radiation shielding designs per year.
Almost every state has some variation of similar requirements, except Wyoming, where there is no mandate for a qualified expert to create an official plan and no inspectors are required to come look at it. That’s not to say that facilities in Wyoming don’t consult with a physicist anyway, but it’s not something that needs to be done before an X-ray room opens for operation.
“Shielding calculations are quite complex and require a number of assumptions to be made, and it is really important that the source of the radiation is understood and everything has been taken into account,” said Jason Launders, director of operations for device evaluation at ECRI.
In theory, radiation shielding designs should be based on the National Council on Radiation Protection and Measurements (NCRP) 147 and 148 reports for diagnostic imaging and NCRP 151 report for radiation therapy, according to Evearitt. Any physicist is going to base their design on those national recommendations but, he says, each state has individual regulations that govern the process.
NCRP 148 and 147 recommends that the shielding be confirmed after install by a qualified expert, but very few states take that recommendation and have it required as a regulation. It’s important to note that this is the case for X-ray, but the rules are much stricter for CT, fluoroscopy and radiation therapy.
To give an idea of the situation in other states — Iowa and South Carolina require shielding designs be submitted and approved before construction, Georgia requires submittal for approval but not necessarily before construction and Colorado doesn’t require submitted approval but an approved qualified expert from the state must have the design on file.
Illinois doesn’t require shielding designs for chiropractor’s offices, but does for CT and other higher-end X-ray equipment. New Mexico and New Jersey don’t require a physicist to do the shielding designs, but state inspectors do measure the radiation leaking through the walls.
Why do these requirements vary so much from state to state? Evearitt says it’s a matter of who is serving on the boards that oversee the rules.
“I think it’s [based on] a lot of the personalities of the people that set these things up originally,” he explained. “As jobs turn over and the state regulators change over time, people don’t have the desire to try to implement a bunch of new regulations. Once something is in place, it’s hard to change the entire practice.”
Launders described a situation in which a facility doesn’t consult with a physicist before embarking on a radiation shielding project as “worrying.” He always recommends consulting a qualified professional that knows the local rules.
Evearitt noted that these situations usually don’t present themselves at the hospital-level because they are much more likely to employ a board-certified physicist as part of their team.
The discrepancies are more common in chiropractic offices and strip malls where there are X-ray machines. But still, 15 percent of the people who call Evearitt don’t realize that they need the shielding done until the vendor shows up to install the machine.
Recently, he got a frantic call from an office in Iowa that already had an X-ray machine and wanted to buy a C-arm. They were working with a national vendor that specialized in getting them set up with training.
“The national vendor didn’t realize that Iowa required a shielding design to be approved by the state before the machine is installed,” said Evearitt. “You would think that this national vendor would know this, but because the regulations are so different from state to state, they thought it could get taken care of within 90 days of installation.”
He was able to get them a shielding design, but the office had to cancel the training and re-schedule the flights for the people who planned to come in.
What does a physicist do?
We’ve established that it’s important to reach out to a physicist to ensure you’re following your state’s requirements, but what else do these professionals do?
According to Bryan Bordeman, operations manager at Global Partners in Shielding, the physicist determines what the shielding specifications are.
“They run their calculations based on the customer’s requirements and they give shielding specifications to the shielding company,” he said. “The shielding company would then determine the best way to construct it concerning feasibility and cost.”
If consulting a physicist is the first thing you do, you may save a substantial amount of money. They might be able to determine whether a room can be moved to another location that’s partly underground to potentially eliminate half of the shielding.
“It would be a costly mistake not to reach out to a physicist,” said Bordeman. “The construction guys are going to over-shield the room or under-shield the room and in both scenarios it’s going to be very expensive for the end-user.”
If the area next to the room is a storage facility that’s only accessed once per year, the wall in between won’t need as much shielding compared to a case where there was an office on the other side.
Alternatively, if a facility is under-shielded and a meter determines that radiation is scattering out everywhere, they won’t be able to admit any patients until this problem is fixed. That could involve rebuilding the facility again, which can cost double what it would have cost if it was built correctly.
Things to consider when choosing a material
Space, source strength and attenuation need to be considered when selecting a shielding material. The main shielding materials used in construction today for diagnostic imaging are lead, gypsum or drywall and concrete, which sometimes includes added materials to increase the attenuation.
“Lead will be for the smaller spaces, but if you’re dealing with high doses then there is high-density concrete,” said Cory Aitken, western senior sales technician at MarShield. “It’s a less expensive product, but it takes up a lot of room.”
In many cases concrete is adequate, but lead is still oftentimes needed, according to ECRI’s Launders.
Historically, lead is associated with toxicity concerns, but that’s no longer a problem once it’s sealed inside the walls. The risk comes into play when the lead is being manipulated during the building or dismantling process.
“Obviously safety protocols needed to be followed when installing or dismantling rooms,” said Launders. “However, the rooms are normally in place for many years and even if the room is used for a different purpose, then the lead won't hurt. Lead is stable, it doesn't release any toxic gases.”
People are attracted to lead because of its lower price point, but long-term costs need to be taken into consideration as well.
“Twenty years down the road when you’re closing down your shop or renovating, the lead has to be taken out and handled in a specific manner, which adds costs,” said Aitken.
Another important thing to consider is how much time you have available for the construction process. If time is limited, prefabricated products may be the way to go, even though they are the more expensive option.
MarShield manufactures pre-fabricated lead-lined wall panels that can be attached to existing walls. The EZ Quick X-ray Shielding Panels can be installed in hours and can be easily rearranged or removed.
According to Atom Physics’ Evearitt, lead is cheap and abundant and the process is already established to have it put on the back of drywall. So how can lead-free alternatives made using tungsten and bismuth compete?
These alternatives started to gain traction because of the toxicity concerns associated with lead, but they are by no means mainstream. The main hurdles are the price of these materials and the difficult process of working with them.
“Lead is a raw material that you can work with,” said Aitken. “If you are working with tungsten, it’s a raw material as well but it’s extremely difficult to machine. Lead can be poured and rolled, but tungsten is a powder form that needs to be broken down.”
In addition, the companies that manufacture these products are dependent on the price of tungsten at any given time.
“Because they weren’t producing mass quantities like lead, they had to buy the raw materials based on an order they got,” said Evearitt. “Week to week and day to day the price of tungsten changed.”
Lead-free alternatives are made up of impregnated polymers that include tungsten and/or bismuth and iron.
Nanotek XYZ is a cost-effective alternative to lead shielding. According to MarShield’s website, it’s a polymer-based shielding material that can be made into thin materials to replace sheet lead and installed on walls with its adhesive backing.
The material could also be used in the form of interlocking bricks to provide thicker shielding as well as curtains, shielded vests, barriers, nuclear medicine vials, etc.
Nanotek RSM offers better X-ray protection in thinner layers and weighs less than lead and Nanotek XYZ, but it’s more expensive. MarShield also offers its T-Flex Impregnated Polymers, which is an alternative to lead wool blankets or solid lead parts in the nuclear industry.
“I think that the more popular Nanotek gets, the better pricing will be,” said Aitken. “With it being such a new product, we are also trying to get more people to adopt it. It’s such a new thing that some people almost don’t believe the studies because it’s so effective.”
Evearitt added that there also needs to be an infrastructure in place to make it easy to order and to make people aware that it’s available.
Radiation therapy shielding
When choosing a material to shield a radiation therapy room, photon and neutron attenuation needs to be taken into consideration. Lead, steel and concrete are the main shielding constituents.
Typically, the higher the energy, the more shielding is required. If a linear accelerator has a maximum photon energy above 10 megavolts, the machine is also producing neutrons.
“If you’re using a lead-type shielding it’s an excellent shielding material for photons, but a terrible shielding material for neutrons in terms of shielding effectiveness,” said Robert J. Farrell, CEO of Veritas Medical Solution.
When determining the time and money involved in a project, Veritas needs to know the workload of the machine, the occupancy outside of the room and how often the radiation will be pointing at a particular barrier.
A typical linear accelerator rotates in a single plane around 360 degrees, and the primary radiation is coming out within a defined path around that arc. Accuray’s CyberKnife machine can point anywhere except straight up, so there is a primary barrier anywhere within the room.
For a typical use-factor on a linac, one-fifth of the time it would be pointing at the east wall, one-fifth at the west wall, one-fifth at the ceiling, one-fifth at the floor. The use factor with the CyberKnife is about one-twentieth because it can point anywhere.
When asked what Veritas’ quickest project was, Farrell said it took about three weeks, but that this isn’t the norm. The client had investment milestones that had to be met, and their original plan to pour concrete was going to lose them money because they couldn’t make those commitments.
“We were able to step in and do the engineering and physics in about three weeks, which involved putting the full gas toward it,” said Farrell. “Shipping the materials and getting them installed was done in about three weeks.”
Typically, a project can take three to five years just for the design process. For a project planned for 2025, Veritas is starting the design phase now by selecting the shielding material that is required for the equipment the facility wants.
Farrell cautions facilities to know what machines they want before building the facility. He is currently working with groups that want to build the facility before they select the equipment and it’s a problematic situation.
“They’re building it in such a way that might become more expensive because they are designing it for the worst-case scenario,” said Farrell. “They could have saved some money had they planned it out a little better.”