Wipe tests to assess 99Tcm surface contamination: effects of surface type, swab type and chemical form

The efficacy of wipe tests for assessing 99Tcm surface contamination was measured. Four types of surface were contaminated with four radiopharmaceuticals and wiped using four types of swab. The fraction of activity removed was measured by direct monitoring for each combination of surface, pharmaceutical and swab. The results obtained showed that wipe tests are neither accurate nor precise. Observed wipe efficacies differed greatly from the customary assumption that 10% of the activity is removed by wiping. Detergent soaked swabs gave a mean efficacy of 40%, although with considerable variation (coefficient of variation 49%). Using these swabs alone the surface type affected efficacy by almost a factor three (floor tile mean efficacy 20%, plastic laminate mean efficacy 57%). In principle this effect might be compensated for by using correction factors according to the surface being swabbed. However, the pharmaceutical type will generally be unknown, and this also affected efficacy by almost a factor of two (eluate mean efficacy 29%, macroaggregated albumin 53%). Overall the results suggest that wipe tests can be used to detect contamination but are unreliable for quantification.