Session Item

The ionisation chamber constancy check is part of good practice in medical physics. Strontium 90 check sources have long been used for this test. However, they are no longer marketed. In this study, a 3D printed device was developed and tested to perform ionisation chamber constancy check with an Iridium 192 high-dose rate afterloader.

The device was printed on the Raise3D Pro 2 printer with a polylactic acid (PLA) filament. It consisted of a 10x10x10 𝑐𝑚3 cube in which a catheter connected to the Iridium 192 high-dose rate afterloader can be inserted in its centre. The cube is attached with bars to PTW RW3 water equivalent slabs where the ionisation chamber can be inserted. Bars were designed to position the cube on the slab centre with a minimum error at each measurement. The tested chamber models were PTW TM31016 (0.016 𝑐𝑚3), TM31010 (0.125 𝑐𝑚3), TM31013 (0.3 𝑐𝑚3), TM30013 (0.6 𝑐𝑚3) and TM34001 (ROOS ). The following tests were performed: repeatability, reproducibility, influence of the measurement environment, effect of the source position and the source replacement.

Repeatability and reproducibility results were lower than 2%. The positioning of the device on 10 cm RW3 plates makes the measurements insensitive to the material on which the measuring device is positioned (metal plate or additional RW3 plates). A 1 mm source position error did not lead to a significant difference in the measurement. The replacement of the afterloader source caused deviations <2% on the measurements.

The developed device offers an alternative to the end of strontium check source availability for the constancy control of ionisation chambers. A tolerance of 2%, conventionally used for strontium check sources, can also be used with this device.