Assembling an Eye Physics or USC Plaque

Plaques which use removable, short lived radionuclide sources such as the COMS, ROPES, and Eye Physiccs plaques can be assembled on-site about 24 hours prior to use, or can be ordered preloaded and sterilized from IsoAid. The radionuclide in BEBIG Ru-106 plaques is not removable so local assembly is not possible.

On-site plaque assembly should be done in a hot lab behind an L block.

LBlock

Prepare to load
  • The radioactive sources (or "seeds") are removed from the shipping vial.
  • A cardboard bowl is placed under the plaque to prevent losing the tiny seeds.
  • The seeds are handled using a long forceps.
  • A "third hand" device holds the plaque by one of its suture eyelets.
PickUpSeed

Load seeds

The seeds are simply dropped into the collimating slots carved into the face of the plaque according to the treatment plan and loading diagram.

PlaceSeed.gif

Glue the seeds

A tiny drop of heat tolerant medical device grade cyanoacrylate adhesive (e.g. Loctite 4014) can be used to coat the seeds in the slots. Use just enough glue to barely surround each seed.

Let the cyanoacrylate dry overnight. If the humidity is very low, put a bowl of water near by. The cyanoacrylate glue hardens very quickly when trapped between two surfaces. The reaction is caused by the condensed water vapour on the surfaces. The water comes from the surrounding air, so the air humidity is a factor that affects bonding capabilities.

The curing reaction starts at the surface of the bonded material and develops towards the centre of the bond. Because of this, thick seams or large blobs of glue may harden less satisfactorily than surface-to-surface bonds with good fit. In a thick blob of glue, a polymerisation reaction may stop before it reaches the centre of the blob. A rule of thumb is that seams thicker than 0,25 mm should be avoided. Thick seams will also take longer time to cure.

To remove the glue and release the seeds, simply soak the plaque in a small beaker (e.g. 100 mL size) of acetone for about an hour. The cyanoacrylate will disolve and the seeds will fall out of the plaque to the bottom of the beaker. The acetone can optionally be captured and used for leak testing the seeds.

Loctite4014Big
Loctite4014Small
Glue.gif