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Information Sheet No. 25

January 2001

General Guidance on Shielding Requirements for Medical X-Ray Diagnostic Rooms

Primary barriers

A primary barrier is one that intercepts the direct beam of an x-ray tube (the primary beam).  Primary barriers are built into mammography, CT and fluoroscopy machines and so secondary barrier protection only is usually required in these rooms.  In general a primary barrier is required for:

• Any surface routinely in the direct line of the x-ray beam, including parts of the walls, floor and/or ceiling (as appropriate) of an x-ray room as well as behind chest stands or wall buckys.  The section of the wall, etc needs to extend at least 300 mm beyond each boundary of the area normally exposed to the primary x‑ray beam.

Acceptable primary barrier:

• a minimum lead equivalence of 2 mm.

Secondary barriers

A secondary barrier is one that shields from scattered x-rays (mainly from the patient) only.

The following are examples of areas typically requiring a secondary barrier:

• the walls of an x-ray room and all doors leading into the room (including changing rooms and toilet doors);
• the floor and/or ceiling (as appropriate) of an x-ray room if in a multi-storey building;
• operators’ barriers, including both the body of the barrier and the viewing window.

The required protection can be achieved in many ways, including the following:

Acceptable secondary barrier - general diagnostic room:

• 1 mm lead;
• one sheet of barytes board (with a lead equivalence of 1 mm at 100 kVp);
• concrete, solid concrete block or concrete block filled with grout or sand, and having a total thickness of not less than 75 mm;
• for a viewing window lead glass or lead acrylic with 1 mm lead equivalence.

Acceptable secondary barrier - CT room:

More shielding is required because these operate at higher energies and high workloads.

• 1.5 mm lead;
• two sheets of barytes board (as above);
• at least 100 mm of solid concrete;
• for a viewing window lead glass or lead acrylic with 1.5 mm lead equivalence.

Acceptable secondary barrier - mammography room:

Less shielding is required because these operate at lower energies.

• two sheets of gypsum plasterboard, each no less than 9 mm thick.  Internal walls lined with one sheet of gypsum plasterboard on each side of the wall stud will meet this requirement;
• at least 8 mm of solid concrete;
• 0.4 mm of steel;
• 8 mm plate glass.

The height of the protective barrier will depend on the circumstances, but in all cases must reach to at least 2 m.  If windows are placed above this height leaded glass may not be required.  Fan lights may be a reasonable alternative in some situations.

When the x-ray facility is constructed it is paramount that the architects and builders ensure the continuity of the protective barrier across joins such as between protective sheets, from walls to doors, and from the body of the operator barrier to the viewing window.  Lead flashing is usually needed to provide continuity of protection, particularly when the protective barriers are in different planes.  The following diagrams illustrate how continuity can be achieved.  Quantities used are for a general diagnostic room.

Double doors

Single-action doors with rebated meeting styles

These are preferred to double-action doors because they can include shielding that gives continuity of the protective barrier (see diagrams below).  They are therefore essential in high scatter situations, such as CT.

Double-action doors

Central gap must be as small as possible - not to exceed 3 mm.
Protective layer must go to the end.

____	1 mm lead equivalent protective layer
	scattered radiation

Door jamb

Viewing window in radiation barrier

Shielding design at a window beading joint

This information is provided for general guidance only.  Please note that there will be some exceptions to the above recommendations.  All shielding specifications must be approved by the Qualified Health Physicist for the facility.  Specific advice should be sought from that person.

 

National Radiation Laboratory           
P O Box 25099               
Christchurch               
NNew Zealand

Phone:     +64 3 366 5059
Fax:         +64 3 366 11
Internet:   http://www.nrl.moh.govt.nz

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