Overexposure of a worker (I-131) – Ionactive Blog archive
Published: Mar 16, 2019
This blog article first appeared on the old Ionactive website site in May 2013. It is not the intention to use every article since Ionactive’s birth in 2002, but there are several blog entries that I think are worthy of a new readership. The following has been through light re-edit.
This is taken from the IAEA News Channel (Nuclear & Radiological Events)
Overexposure of a worker (I-131)
[28 February 2013, Finland, MAP Medical Technologies Oy, posted 08 April 2013, INES = 2(Final)]
A laboratory worker was contaminated with I-131 in a radiopharmaceutical company on February 28th, 2013. The worker was wearing two pairs of gloves and, when changing gloves, had noticed a break in the right inner glove, but not any obvious break in the outer latex glove.
Only 3-4 hours later, routine monitoring revealed heavy contamination of the dorsal part of the right hand. Immediate actions to decontaminate the hand were undertaken on site. On the next day, besides persisting heavy contamination of the hand, activity was also found in the thyroid gland, and the Finnish Radiation and Nuclear Safety Authority (STUK) was notified. Stable iodine had not been administered.
Based on original measurements on site and later follow-up at STUK, including surface contamination measurements and whole body counting, the original activity of the hand was estimated at 11 MBq and the equivalent skin dose at 25 Sv, affecting an area of about 10 cm2. The estimated equivalent dose to the thyroid was 430 mGy and the estimated effective dose 22 mSv.
On her first visit at STUK, the worker was advised to wear a glove and change it frequently in order to protect the surrounding and promote decontamination by sweating and washing. Three days later little activity was left in the hand. 11 days after the incident the skin was dry and slightly desquamating. After 15 days the skin was intact with no desquamation left. No further signs of skin damage have occurred.
The incident log for the above event can be read at the following link: IAEA News Channel - Overexposure of a worker (I-131)
Just look at the headline figures here: 25 Sv to part of the hand, dose to the thyroid 430 mGy and effective whole body dose estimated at 22mSv.
It is very important to note that this is not a nuclear incident (even though it's reported on the IAEA news event channel). This is very unlikely to hit the media - will be missed by most - but the doses received in this incident ARE NOT common in the nuclear industry (far from it) - under routine or accident situations to workers or members of the public. [2019 – did not make much of a media impact in 2013).
According to their website, Map Medical Technologies develop and manufacture radiopharmaceutical for nuclear medicine professionals. There are many similar companies like this located all over the world doing similar work. Looking at the report of this case it makes us wonder how many similar exposures of this type might go undetected. There appears to have been a PPE (double glove) failure, combined with a lack of monitoring so that the hand contamination went unnoticed (for up to four hours). It is not clear if the thyroid contamination is a result of transfer from the hand, or due to direct intake at the workplace (during the initial contamination incident). We are inclined to think that latter - clearly radiological hygiene standards were considerably below expectations. [2019 – It is not helpful that the ‘nuclear’ word ends up in ‘Nuclear Medicine’, not that we have anything against anything nuclear!].
A lack of radiation / contamination monitoring
If you look at other incidents Ionactive has commented on you will see a common theme. Lack of monitoring. Ionactive spends considerable time during training courses drilling (gently) into delegates the fact that monitoring (passive, active, direct and in-direct) are the ‘eyes, ears - indeed all the senses combined' - and the only way to understand the radiological environment surrounding you. Without adequate monitoring you are effectively ‘blind' - and when blind significant radiation exposures can be delivered leading to events of this type.
Is 25 Sv local dose really possible?
Ionactive was curious to see if the estimated dose delivered to the hand was realistic (since 25 Sv is a massive localised dose, and 11MBq is a modest activity used in the medical sector). Ionactive Varskin 3 code (a dosimetry model for surface/skin contamination). We used a skin density thickness of 7 mg / cm2, a 2-d disk (10 cm2), skin averaging over 10cm2, 11 MBq of I-131 with an exposure time of 4 hours. Ionactive results were around 8 Sv (Gy) which is about a 1/3 reported above. The code was run again with different geometry and skin thickness and you can approach 25 Sv (Gy), so we presume the dose calculations run for this individual would have been very specific. So, the basic findings are that a localised radiation dose of 25 Sv is most certainly possible under the conditions outlined in this incident. [2019 – whilst this is an equivalent dose to the hands, the use of the unit of the Gray (Gy) it probably more appropriate here].
Ionactive then wanted to explore using gloves. We have no idea what type of gloves were worn so we used neoprene gloves with the following specification: density 1.23 g/cm3 with the thickness of 0.4mm. Assuming these gloves were worn intact with the contamination on the outer surface, then the skin dose over four hours is reduced by about a factor 8. With two pairs of gloves, the dose to the skin over the exposure time reduces by a factor of about 50 (so using the original supplied data you might be looking at a hand dose of 0.5 Sv rather than 25) - still considerable, but considerably less.
The results of the calculations show that regular monitoring of the gloves during the work is a key measure to reducing exposures.