SU‐E‐T‐251: Prototype QA Device for HDR Source Position Simulator

Abstract

Purpose: Design and build prototype device to perform baseline and ongoing, monthly, tests of resistance‐tolerant, smooth, dummy HDR source, position‐measurements under controlled conditions. Methods: Seven helical loops of Nucletron‐compatible catheter were wound onto the surface of a 10″ long, polyethylene tube which was 1.875″ diameter. A Nucletron HDR transfer tube could be connected between a Source Position Simulator and the entrance, 1st top helical loop end (Figure 1). Results: The 2010 SPS was attached via the transfer tube to the SPS QA prototype. The SPS wire was advanced smoothly from the start position (1030mm) to the maximum extension at 1469mm (using the advance yellow edge of the SPS marker). There was minimal cumulative resistance braking of the wire source thru the last 50mm before that max point at 1469mm. Next, the older, heavily‐used, 2004 SPS was attached via the transfer tube to the SPS QA prototype device. This SPS wire would not advance to the limit smoothly. Actually it met some modest resistance at around 1152mm (identical to the conditions of the Medical Event). The SPS wire was more firmly pushed through that zone of resistance and advanced, with increasing resistance to about 1262mm before the decision was made not to push more firmly. Conclusion: It is possible, using cumulative resistance at increased path lengths in the helical catheter, to objectively measure a distance‐to‐stop. Any motion that is not pushably‐smooth and meets any resistance short of the max finish at 1469mm indicates the beginning of damage. That signal should suffice to warn that ‘it is time’ to refurbish or replace the SPS. Results show a proper range of cumulative resistance‐induced retardation of the pushing motion of the wire thru the full motion range in QA simulation. The clinical condition of use of an SPS is accurately emulated in this device.