“Wipe Test Wednesday.” A System to Improve Working Practice.

Introduction: A Nuclear Medicine staff member received extremity contamination from a door handle in October 2022. Following this incident door handles were added onto the list of areas that undergo routine contamination monitoring at end of day.

To further assess if contamination is occurring frequently, routine wet wipe testing of high frequency touch points, including door handles and medical equipment, was implemented to assess for loose contamination. This system of testing has fondly become known as "Wipe Test Wednesday". Routine wipe testing gives the department confidence that our working practices are safe, and when contamination is discovered it allows the department to review and assess how the contamination has occurred so changes to working practice can be implemented.

Methods: During "Wipe Test Wednesday" the surface of eight random door handles, located in the controlled and supervised areas of the Nuclear Medicine department, are wiped. For each wipe test a fresh MediSwab (small sterile alcohol wipes) and disposable tongs are used. Once wiping is complete each MediSwab is put into a plastic test tube and capped. Two unused MediSwabs are also put in individual test tubes and used as Backgrounds. All ten tubes are then placed in a rack and measured on a Hidex Automatic Gamma Counter (AGC) system using an open window (15 – 2,014keV) with a counting time of 10 minutes per tube.

The HIDEX output for each Wipe Test Sample (WTS) is recorded in Counts per Minute (CPM). An average of the two backgrounds (Bkg) is calculated and subtracted from each sample to give a Bkg corrected CPM. This is then converted to Counts per second (CPS) above background for each WTS.

When performing wet wipe tests the assumption is that only 10% of the surface contamination is removed and measured, therefore any WTS results measuring 10 CPS above background is considered to be contaminated, classed as a FAIL, and is flagged for further investigation.

For FAIL results the energy of the contamination is checked from the HIDEX spectrum outputs to determine the radionuclide. Additional wipe tests of other high frequency touch points (for example worktops, desks, bins etc) are then also taken. This is to check for further secondary contamination. Possible causes for the contamination is also investigated.

Results: Out of 176 WTS only one FAIL was recorded. This was contamination of a scanning room exit door with ^99mTc. More in-depth contamination monitoring of other areas was performed at this time, but none found. A review of the scanning room workload on the day the contamination was found showed a V/Q scan and centre of rotation QC had been performed. Either study could have been a source of the contamination, with spread likely occurring via contaminated gloves that were then disposed of prior to monitoring, as no contamination of staff was recorded on this day.

Conclusions: Although 175/176 WTS passed contamination testing, the fact that contamination was found on a door handle is concerning. If contamination of this sort is not found and decontaminated immediately, contamination of staff and other areas may occur.

"Wipe Test Wednesday" reminds all staff of the importance of safe practise and to follow radiation safety principles. These include changing gloves as soon as possible after handling radioactive materials, and performing regular personal monitoring to assess for contamination.

Future work includes expanding testing to other days when different NM procedures are performed, and introducing routine spot checks for staff hand contamination.