My "Hot" delegate
Published: Jul 28, 2024
Prelim
A recent post on a medical email base reminded me of an experience many moons ago (well over a decade). It required a high degree of dynamic risk assessment on the spot. It is one of those stories you might tell where colleagues / associates give you ‘the look’ (such as ‘is this really true…’ or ‘are you exaggerating for effect…’ etc). What follows is a true experience and is as close to being accurate as I can recall. To give anonymity to places and persons I have a changed a few details, but this does not materially change the story.
Ionactive was running its regular two-day Radiation Protection Supervisor (RPS) course at a venue in the South of the UK. These were regular monthly fixtures and were open to all, so we would have a good mix of delegates from all over the UK attend. The course was residential, so delegates arrived on the Monday and attended day 1, stayed overnight at the hotel based at the venue, and carried on training Tuesday.
The training room was typical - 18 delegates sitting two to a table, set out in a horseshoe shape with Ionactive on a table at the base. On our table facing the delegates were a range of objects such as radiation monitors, new and old dosimetry, personal air samplers, uranium glass and other radiation related objects. At various times during the training objects would be picked up to illustrate a point on the overhead projector display, or as a discussion point.
Although the training was planned to an agenda, the nature of Ionactive training and the variety of delegates meant that often subjects (and objects) would be discussed / demonstrated according to the flow of delegate interest and questions asked. On this occasion the various radiation monitors were not demonstrated or even switched-on during Monday, something that would be a key issue on Tuesday.
My “Hot” Delegate
On the Tuesday the delegates had breakfast, cleared their overnight rooms and were all seated back in the training room at 0900. Someone mentioned background radiation and the fact that they had seen ceramic in their hotel room (ceramics can contain zircon sand). Time to switch on a 44A mini 900 monitor and let the group ‘listen’ to background radiation.
Something was up?!!
A 44A (NaI scintillation-based detector) normally shows between 5-10 CPS, which is a reasonable crackle and lively enough to allow the delegate to ‘hear’ background radiation. But something was up – the 44A was reading 50-75 CPS. The cable was waggled, the monitor was turned on and off, but the higher-than-expected count rate continued. Convinced it was a monitor fault I continued to talk to the delegates as if nothing was wrong, whilst trouble shooting (this multitasking is not easy). I switched on a dose rate monitor (cannot recall what type) and it was showing 1 micro Sv/h, nothing huge but certainly higher than expected background. Could there be anything in the room I was unaware off? Was something going on outside (a nuclear incident no less?). Grabbing the 44A monitor again, and still talking to the delegates as if all was ok, I moved to my left towards a window which was positioned behind the end of the U-shaped seating. As I moved towards the window the count rate went up – so something going on outside I thought. But as I got right up to the window glass, passed the delegate sitting at the end of the U shape, the count rate dropped. Hmmm ??
Reversing direction I moved backwards towards the presentation desk, passing by the end delegate – the count rate peaked at 100 CPS – directly in line with that delegate / trainee (let’s call them “X”). I moved closer to X, and the count rate increased to 200 CPS (was about 1m away). I asked X if I could move slightly closer – “yes” they said. At about 0.5m we had some 600 CPS showing. It seemed to be coming from their head, as when the probe was dipped towards their trunk the count rate dropped a little.
Now convinced they were the “source” I asked if I could monitor them. Yes replied X. It did not take long to discover the source of the radiation was their thyroid!! I recall nearly off scale on the 44A.
What was the dose rate I wondered? I went and grabbed a trusty 451 ion chamber and proceeded to measure the Thyroid directly. At around 1m the dose rate was about 10 micro Sv/h, tending to nearly 1mSv / h near contact (I recall not wanting to get too personal with the radiation monitor).
I noted that the delegate next door (calculated / measured later) was in a radiation field of about 5 micro Sv/h, and I recall at the time thinking “well that is neat, about the same as flying at 40,000 feet in an aircraft … I might need that comparison later”.
At this point I did not have any actual answers. So I turned this situation into a live training / risk assessment event and carried on regardless (on reflection I am not sure if this was the best course of action, but it was what I did).
My "Hot" Delegate
- Ionactive: would you like to tell me something?
- “X” : ahhh that might be the Iodine procedure from last Friday.
- Ionactive: I-131 procedure!? What did the hospital / clinic advise?
- “X” (grinning): don’t sleep with your partner, don’t hug your kids, don’t use public transport and have a week off work …
- Ionactive: but… you are here, on our Radiation Protection Supervisor training course?!
- “X”: I know, did not want to miss it!! [Pause – this left me slightly struggling to find the right words… ]
- Ionactive: right, OK. Well we better make the most of this.
What to do with a “Hot” delegate?
One option was to send them packing. However it was now day 2 and we had just started the first morning session and I did not want to interrupt the training further to deal with this most unusual 'admin’ issue. So the first three things I did were:
1) Explain to the rest of the delegates (very briefly) what the issue was (I am pretty sure most knew by now anyway).
2) Move the group around the U-shape (please all budge up!), so that the maximum dose rate for delegate No2, sitting next to X, was now background.
3) Reminded the whole group that sitting next to X in the normal ‘two to a table’ position yielded a dose rate of approximately 5 micro Sv/h. about the same experienced at 40,000 feet in an aircraft at UK latitude. I emphasised the importance and usefulness of comparators when determining radiation risk.
During this initial ‘post dose rate shock’, I stayed clear of criticising the delegate too much (or the hospital who may have not explained the situation clearly enough).
With the situation stabilized I set about restarting the training which was about to consider – practical radiation protection.
Time – I recall setting up an ion chamber and knowing the dose rate asking the delegates to assess / guess the accumulated dose over 1 minute. Several micro Sv were measured (X held the monitor close to their neck).
Distance – I knew that inverse square law was going to be difficult to demonstrate, even with a live source. It’s not exactly a point source, and only a couple of m’s brought the dose rate down to near background (delegate 2 was thankful for this). Nevertheless we managed to have some willing volunteers to use a 44A probe and some reasonably inverse square relationship were noted in the first 10’s of cm from X’s neck.
Shielding – in the Ionactive tools box was a sheet of code 7 lead (just over 3mm). The lead would provide about 1 HVT (1/2 value thickness) for the gammas from I-131. [Aside: I-131 is a significant beta emitter and an unshielded source should be treated with Perspex first before considering lead shielding. However, in a post-training event “what on earth has just happened”, I estimated that much of the beta dose would be absorbed by the body tissue of X]. In any case the 10cm x 10cm lead plate, nearly 400g, did the trick and indeed provided an HVT when using the 44A probe.
Then it was coffee break time.
The hotel Factor
We had a 20-minute coffee break. I took X back up to his room – on the pretence that something may have been left. Several things were then shown to be rather fortuitous:
A) The room had not yet been attended by morning staff.
B) The room was on the first floor, at the end of row.
C) The bed was on the outside wall, so negligible exposure potential to anyone else the other side of the wall.
D) Remarkably (!), there was minimal evidence of contamination (not really knowing what to expect given that practical nuclear medicine was not my area of expertise). Nothing above background on the bed, but some in the toilet bowl and some on the shower tray. They were dealt with by yours truly (using the ‘aqueous route’).
To this day I think about liability - potential exposures and what is in the best interest of all persons concerned. I cannot recall all my thinking at the time, but in terms of hotel staff (reception, those serving dinner, those clearing plates etc), I assessed that exposures would be negligible and not materially different to background exposure on a typical day in the area. I considered this to be valid for all who had been close to X (i.e. other visitors and staff – so any other person outside the training room). My conclusion was that to raise this as an issue with the hotel would cause more harm, anxiety and concern than any potential radiation exposure actually warranted. Notwithstanding any moral or other legal judgement, I do believe this decision was correct at the time. In the weeks after the event I did some more detailed back of envelope calculations to support my original decisions.
Readers who are surprised by this story, need to realise that you could inadvertently come into close contact with a nuclear medicine patient in a hospital corridor, waiting area, café, on the bus (despite the advice regarding non-use of public transport), as you go about your business. Weirder perhaps, you might come across your neighbour’s radioactive cat!
The chances of encountering any of these situations is low, but you are unlikely to have a radiation monitor switched on ready to go, so you will never know!
How were the other delegates?
I offered all delegates a 1-1 session if they felt this was needed to explain risks provide reassurance etc. However, this was not required as the whole group were happy to discuss the issues together. All accepted, including delegate 2 sat next to X, that the exposures were low with negligible risk. However, most of the delegates had no idea about nuclear medicine and were wide-eyed when I discussed in greater detail (compared to my other routine RPS courses), the nature of the medical practice. Producing walking, talking, and sometimes leaking radioactive sources is a thing!
[Aside: years later I have had many of the same delegates back taking Ionactive RPS training (sadly not X), and quite a few recall this incident with errrr fondness so it seems!].
Final thoughts
Expect the unexpected. Never assume.
I had toyed with the idea of a more detailed dose reconstruction for this blog, but this event was a long time ago and I don’t think I have any more reliable information to work with in 2024. I may release a companion blog entry later in the year to provide a dose assessment using typical activity and retention data etc.