X-Ray Room Shielding Requirements: ASimple Guide

If you are building an X-ray room, you may be wondering: how much lead does an X-ray room need? There is no one answer. Some X-ray rooms need lead in several walls. Others may need very little added shielding. The answer depends on how the room will be used.

A shielding design looks at the X-ray machine, the room, and the people around it. Then it tells the design team what shielding is needed.

Why does an X-ray room need shielding?

An X-ray machine makes radiation when an image is taken. Some of that radiation travels in the main X-ray beam. This is called primary radiation. Some radiation also scatters from the patient and other objects. There is also a small amount of radiation that can come through the X-ray tube housing. These are called secondary radiation.

The walls, doors, windows, floor, and ceiling may need to reduce this radiation before it reaches people outside the room.

NCRP Report No. 147 is one of the main technical guides used in the United States for medical X-ray shielding design. It explains how primary and secondary radiation should be considered when designing barriers.

What is a primary barrier?

A primary barrier is a wall, floor, or other surface that the main X-ray beam may point toward. This is important in a general X-ray room because the X-ray tube can often move.

For example, the beam may point down toward the X-ray table during one exam. It may point toward a wall-mounted image receptor during a chest X-ray. NCRP 147 says that barriers that may be hit by the primary beam should be treated as primary barriers.

This is one reason you cannot simply put the same amount of lead in every wall. Each wall needs to be looked at on its own.

What is a secondary barrier?

A secondary barrier is a barrier that is not expected to receive the main X-ray beam. It protects people from scattered radiation and radiation from the X-ray tube housing.

A wall may be a primary barrier in one location and only a secondary barrier in another location. The shielding design should show the correct requirement for each part of the room.

What determines how much shielding is needed?

Several things matter. The physicist will look at:

• What type of X-ray equipment will be used
• How many patients will be imaged
• What types of exams will be performed
• Where the X-ray tube can point
• Where the table and wall stand are located
• How far nearby people are from the X-ray source
• What rooms are next to, above, and below the X-ray room
• How often those nearby spaces are occupied
• What the walls and floors are already made of

This is why two X-ray rooms that look almost the same may need different shielding.

Does every wall need lead?

No. Lead is only one shielding material. Concrete, gypsum wallboard, and other building materials also reduce X-rays. NCRP 147 discusses several types of shielding materials and recommends calculating the amount of protection needed before choosing the final barrier.

Sometimes the existing wall or concrete floor already provides useful shielding. The goal is not to put lead everywhere. The goal is to provide the right amount of shielding in the right places.

What about the X-ray control booth?

The person operating a fixed X-ray unit should have a protected place to work. NCRP 147 recommends a permanent control booth or other fixed shield that protects the operator. It also says the operator should be able to see the patient during the exam.

The report also gives detailed recommendations for control booth design. For example, it describes a booth at least 2.1 meters high and recommends placing the exposure switch so the operator cannot make an exposure while standing outside the protected area. State rules may add other requirements.

What about doors and windows?

Doors and viewing windows are part of the shielding design too. If a wall needs radiation shielding, an opening in that wall should not create a weak spot. A shielded door may need lead or another protective material. A viewing window may need lead glass or lead acrylic.

The shielding report should clearly show the required protection so the architect and contractor know what to order.

What about the floor and ceiling?

The floor and ceiling may also need to be checked. This is especially important when there are offices, treatment rooms, or other occupied spaces above or below the X-ray room. Concrete floors often provide a large amount of shielding. However, the physicist should know the type and thickness of the floor before giving it credit in the calculation.

What radiation level is the shielding designed for?

NCRP 147 uses different shielding goals depending on who normally uses the area. For a controlled area, such as certain areas used by trained radiation workers, the report recommends a shielding design goal of 0.1 mGy per week. For an uncontrolled area, such as an office, hallway, waiting area, or other space used by the general public or workers who do not routinely work with radiation, the report recommends 0.02 mGy per week.

These are design values used when calculating shielding. State regulations may also apply.

When should the shielding design be done?

The best time is early in the project. Do not wait until the lead has already been installed. A shielding physicist should review the room after the equipment location and floor plan are known but before the construction drawings are final. That makes it much easier to change a wall, door, window, or equipment location if needed.

What information is needed?

For most X-ray shielding designs, it helps to provide:

• A scaled floor plan
• X-ray manufacturer and model
• Equipment location
• Room use
• Expected number of patients
• Rooms next to the X-ray room
• Information about the floor and ceiling
• Project city and state

The shielding physicist can use this information to calculate the protection needed for each barrier.

Do not guess at X-ray room shielding

There is no standard lead thickness that works for every X-ray room. The safest and often most cost-effective approach is to calculate the shielding for the actual room. A good shielding design protects workers and the public without adding shielding that the project does not need.

Need an X-ray shielding design? Heartland Physics provides shielding calculations for diagnostic X-ray facilities. Send us your floor plan, equipment information, and project location to get started.