How X-Ray Room Shielding Is Calculated and Built

What shielding must achieve

Shielding attenuates the primary beam, scattered radiation from the patient and leakage radiation from the tube housing. The design goal is to keep the dose in each adjacent area below a limit for that kind of area, with a stricter limit for areas occupied by the public than for areas used only by radiation workers.

The key point is that shielding is room-specific. Two rooms with identical equipment can need different barriers if their workloads, floor plans or neighbouring areas differ, so a generic figure copied from another project should not be used.

How the calculation works

A recognised method, such as the approach in NCRP Report 147 or equivalent IAEA guidance, combines several factors: the workload (the amount of radiation produced per week), the use factor (the fraction of time the beam points toward a given barrier), the occupancy factor (how much time people stay behind it), the distance from the source and the design dose limit. The result is the attenuation needed, which is converted to lead thickness or an equivalent.

The calculation is normally carried out by a qualified expert such as a medical physicist or radiation protection expert, who also documents the assumptions. Provide the expert with the equipment model, its maximum kV and mA, the planned examinations and a scaled drawing of the room and its neighbours.

Lead walls, lining and equivalent materials

Common solutions include sheet lead bonded to plasterboard or plywood, barium-based plaster, concrete and solid brick or block of sufficient thickness. Each material is given a lead equivalence at the energies used, which is the thickness of lead that would give the same attenuation. For many general radiography rooms the wall requirement is in the order of one to two millimetres of lead equivalent, but the exact value must come from the calculation.

Barriers normally extend to a height of about 2.1 m above the finished floor, or higher if the geometry requires it. The ceiling and floor must also be assessed, especially when the room is above or below an occupied area. Our guide to the X-ray room lead door and glass covers doors and windows.

• Sheet lead on board: thin, predictable and easy to verify
• Barium plaster: continuous finish without joints
• Concrete or brick: heavy but needs no lead lining if thick enough
• Lead-lined doors, frames and leaded glass

Construction details that often fail

Most shielding problems occur at details, not in the main wall. Lead sheets must overlap at joints, door frames and electrical boxes must be shielded behind, and any penetrations such as conduits, ducts and pipes must be arranged so that radiation cannot take a straight path through them. Fixings through the lead should be minimised and covered.

Coordinate early with the architects and the contractor about where lead is installed in the build sequence, how it is protected during works and who inspects it before the finishes are applied. Our article on X-ray room design requirements and the one on site preparation cover related topics.

Verification, regulation and next steps

After the room is built and the equipment installed, a physicist performs a radiation survey with a calibrated meter to confirm that the barriers perform as designed. Keep the calculation, drawings, inspection records and survey report in the room file.

In the UAE, radiation sources and facilities are regulated, and shielding design and licensing procedures should be confirmed with the relevant authorities such as FANR and the health authority that licenses your facility. For installation planning with the equipment you intend to buy, see our installation services or contact Beckfinity.