Shielding design for a Cs-137 rod-type standard point source for well chamber constancy checks

Well type chambers are used for radioactive source calibrations in brachytherapy, but do not provide radiation shielding. Routine constancy checks on a well chamber are required between periodic secondary standard laboratory calibrations to ensure consistent device performance, and ultimately to ensure accurate patient dose delivery. In this work, a method is described to provide suitable shielding for a Cs-137 rod-type point source to enable use for constancy checks. A novel plunger-type shielded housing was designed and constructed for the Cs-137 source that when combined with a suitably shielded well-chamber container minimised user exposure during constancy checks. The designed shielding proved effective, and a constancy test routine was established and used for the past 16 months. The well chamber showed consistent performance (0.12 ± 0.18 % from the baseline) and no increased exposure was reported on users’ radiation badges. © 2016, Australasian College of Physical Scientists and Engineers in Medicine.