Tag: shielding

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PET Shielding

Ever wonder what goes into shielding for a PET imaging facility?

No? Well, I’m going to show you anyway.

First you need to find a Qualified Medical Physicist (like me) to develop a shielding design for you. The shielding design gets turned into a set of blueprints for the lead contractor to work with.

Shielding blueprint

Then you need lead. Lots and lots of it.

Lead bricks
Lead lined plywood sheets


This is a layer of 1/4″ thick lead sheet lining the floor. The strips cover up the seams between the lead sheets so that there are no gaps. Depending on what’s underneath, the floor may require as much as 1″ of lead.

Floor shielding
Lead sheet used for floor shielding

For the walls, you’ll need stacks of 1/4″ or 1/2″ lead sheet attached to 3/4″ plywood, like these

Lead wall sheets

Thinner lead sheets are usually glued to drywall, but that doesn’t quite cut it for the thicknesses required for PET shielding.

The lead/plywood sheets go up like this

Lead/plywood wall

The sheets are also interlocking to eliminate the gap between sheets

Interlocking lead joints in the plywood wll

Depending on what’s on the other side of the wall, you’ll need bricks too. This is a stack of 1″ interlocking bricks. Sometimes your wall might even need up to 2″ thick bricks.

Stack of lead bricks

This is what the brick wall ends up looking like

Lead brick wall

The bricks are screwed into the metal studs for support. Thicker brick walls require additional support and are usually constructed between two sets of studs.

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Review: NCRP 147 – Structural Shielding Design for Medical X-ray Imaging Facilities

Amazon’s review system apparently wasn’t working when I tried to submit this there, so I’ll put it here instead (I probably would have put it here anyway).

A few months ago, I unexpectedly received a fat FedEx envelope containing a draft copy of the much anticipated rewrite of NCRP 49: Structural Shielding Design and Evaluation for Medical Use of X-Rays and Gamma Rays of Energies Up to 10 MeV. Turned out it came to me because I’m on the AAPM Diagnostic Imaging Committee, and committee members were asked to review the draft to make sure there weren’t any glaring errors or anything. Sweet, so I dug in. Been hearing about this thing for years, and was eagerly awaiting it’s completion, like many other medical physicists out there.

A few weeks ago, I was rewarded for my efforts as a committee member reviewer by a surprise complimentary copy of the newly published NCRP 147. Even sweeter. And a hardcopy version to boot.

NCRP Report 147: Structural Shielding Design for Medical X-Ray Imaging Facilities

This is an invaluable upgrade to NCRP 49, and probably needs to be added to the collection of every medical imaging physicist that does shielding calculations. The focus is on shielding for imaging rooms, so there is much more relevant content for imaging physicists than there was in NCRP 49 which covered imaging and therapy shielding. New methods and techniques have been introduced which results in somewhat less conservative shielding requirements than what would have been required under the ultraconservative NCRP 49. Chapter 5 provides sample shielding calculations for just about every type of imaging room there is. This is a well written and much needed update to the original NCRP 49.

Even though I’ve already been through the draft, I’m going through it again, because this is the kind of thing medical physicists need to know like the back of their hand. Much of the content and calculations are similar to what was in NCRP 49, but there are enough new things in the rewrite that makes it worth studying thoroughly.