Experimental measurement of dosimetric parameters relevant to radioactive needlestick injury

Nuclear medicine healthcare workers are exposed to the risk of radioactive needlestick injury. To quantify the severity of this risk, the activity deposited into the skin and the injury depth have been experimentally measured for input into skin dosimetry program VARSKIN+. Agar test objects were pierced by hand with a needle containing Tc-99m Hydroxymethylene Diphosphonate (HMDP). The deposited activity was measured by contamination monitor and converted into deposited volume. Injury depth was measured with a ruler by piercing the test objects with visible dye.

The median volume deposited into test objects without gloves was 100 ± 50 nl (standard error) (interquartile range (IQR): 50–320 nl). Through one glove, this was reduced to 50 ± 20 nl (IQR: 30 - 140 nl), however, the difference was not significant (p > 0.1). The volume deposited through two gloves was highly variable due to the increased force required to puncture. The median injury depth was 4.0 ± 0.4 mm (standard error).

Decontamination efficacy was investigated by rinsing alone, with hand soap and by application of decontamination agent RadiacWash. All decontamination methods were found to significantly decrease the activity deposited (p < 0.001). Test objects rinsed for 60 s had a mean reduction of 42 % ± 6 % (95 % confidence interval). There was no significant difference observed between decontamination methods. This may be due to differences in absorption time between the sample groups.

Skin dose estimates have been calculated in VARSKIN+ using the results of the experiment. For injuries without gloves, involving 1011 MBq/ml of Tc-99m HMDP, a skin dose of 11 ± 5 mSv (propagated standard error) was calculated. Immediate decontamination under running water is recommended to reduce the dose. Further research is encouraged to investigate the protection offered by gloves.