I was reading the Daily Mail just before Christmas while waiting for my dental appointment when the headline about dementia rates falling since the leaded petrol ban in the UK in 1999 grabbed my attention. It said that heavy metals, such as lead, have been linked to a higher incidence of dementia, according to research based in Toronto, Canada.
The research suggests that high dementia rates may have been caused by exposure to lead from car exhaust fumes, and that the gradual switch to unleaded petrol in the 1970s and 1980s, and the complete ban on lead in petrol over 20 years later is bringing down the rates of dementia and will likely continue to fall in Europe, the US and Canada.
However, due to an increasing and ageing population, the total number of people with dementia has been steadily rising but a recent study from Harvard in the US has claimed that the overall dementia rate, the percentage of people who will go on to develop the disease is actually falling by up to 15% per decade.
The Daily Mail article (link below) set my mind racing in that when I qualified as a DCR therapy radiographer in 1982 I was continually exposed to lead and later alloys of lead and cadmium and so should I start to worry as to the impact of this on my health in later life?
So now that I approach retirement having just received my NHS pension release information letter it’s great news that in real terms dementia rates are decreasing but will that narrative apply to me or my DCR peers and are some of us sitting on a dementia time-bomb due to historic lead exposure?
Mary was the Head of the School of Radiotherapy at the Middlesex Hospital when I arrived there in 1980 and was a fine teacher and quietly motivational mentor who really believed in me. I think that Christine Souter (if I am correct that actually it is her) was the then President of the Society of Radiographers. As you all know I’m still heavily involved in Radiotherapy today but my time is almost up! Where have those 40 years gone? I guess that is why I am writing my blog to find out.
Read more on why switching to unleaded petrol may be behind dementia rates falling 15% each decade in Europe and North America here: https://www.dailymail.co.uk/health/article-7810811/Switching-unleaded-petrol-caused-dementia-rates-fall-15-year-Europe-North-America.html
Lead shielding exposure in radiotherapy
The lead and alloy shielding blocks we used on our original MEL Linear Accelerator or Cobalt Units were regularly handled without any nod to health and safety, we didn’t wear any gloves either in an era where Multi-Leaf collimators were still many years away. Asymmetric jaws on Linacs didn’t really arrive until the late 80’s when the use of lead and alloy blocks would start their planned decline.
The Cobalt units only had symmetric jaws and so handling lead blocks was common place, fitting into what we referred to as compression-based lead shadow trays to deal with angles that were not 0 or 180 degrees.
When working in the mould room as every student had to on a regular basis as part of our training meant further exposure to lead in unadulterated sheet form. These sheets were often cut with heavy duty scissors and then shaped with an embossing mallet onto a plaster model of the patient and the electron treatment field cut out by hand using a manual, “jewellery style” thread saw creating lead filings or by blunt paring knife, once again performed in an uncontained or non-air-filtered environment. Care had to be taken to clean any residue using a vacuum cleaner!
Creating individualised megavoltage shielding would be made by filling a Styrofoam mould with hot, low melting point alloy made by MCP in the UK, bubbling away at circa 69 or 70 degrees in a cauldron without any specialist air extraction system provided at all to capture aerosols. These blocks had the advantage of being divergent (the simple leads blocks above weren’t) and made on a pantograph with a hot wire that mimicked the beam and source to axis/isocentre distance. The thermostats on the melting pots were poor and the temperature regularly rose above the melting point so that toxic vapours were always possible and wearing a mask would now have made complete sense and prevented inhalation but we didn’t. These large blocks were handled manually when used on the treatment machine and patient, positioned on a simple plastic tray mounted on the head of the machine that contained the outline of the blocks to enable the correct positioning of them and the beam centre. MCP 69 (sometimes known as Cerrobend or Wood’s metal) contained Bismuth (50%), Lead (27%), Cadmium (10%) and Tin (13%) (not a healthy sounding mixture) and the change from 70 to 69 was to allow for less void or cavity formation in the block when setting.
When you worked on the superficial low kV skin unit, using 1 or 2mm lead sheet was standard practice for shielding parts of the body that you wanted to miss and handled for much of the working day with bare hands. Many cut outs were standard shapes and sizes while others were made to measure on the spot, once again without the need to wear gloves.
I then went on to work at Mount Vernon Hospital in Northwood for almost 6 years as the lead radiographer (lead as in leading the way and not Lead as in Pb) where my exposure to lead and cadmium continued unabated as it did to some extent to the radiographers working on the machines. I did spray all my mould room “products” with a special PVC coatings and often the lead masks were covered in some wax to prevent bremsstrahlung radiation when applicable but also helped as a protective measure when manually handled. Very often a radiotherapist (clinical oncologist now) would ask me to shave a few millimetres off the alloy block when check films were taken. This was not great as it created toxic shavings but if the patient had to wait for further modified blocks to be made it would seriously delay their treatment. We should have said no but we didn’t unless a major change was required.
Free milk at work and not only at school!
Due to this exposure the hospital provided me a free pint of milk a day as a way to assist the removal of heavy metals from my body and so there was some acknowledgement that there were some health and safety issues at play here. I liked milk but was not sure how it really helped although now there is research that shows milk can be contaminated with scant levels of heavy metals and exposure to this by infants can also now be considered a health issue in some countries in Europe!
Advent of MLC and phasing out of the DCR
The Multi-Leaf collimator arrived clinically circa 1993, installed permanently on conventional Linacs and so from then on a therapy radiographer’s exposure to lead and heavy metal alloys was to exponentially decrease as more machines with MLC were delivered and installed. I would estimate that by 1995 or shortly thereafter all machines ordered and installed in the UK had MLC as standard.
This coincided with the widespread introduction of BSc courses in radiography during 1993, when the DCR was phased out and so if you have a degree your exposure to lead will have likely been drastically reduced or non-existent!
Out of interest, the NOMOS Peacock system (first delivered circa 1992 ) was the first dedicated IMRT system based on an innovative collimator using binary moving leaves integrated with machine rotation, independent couch control and a dedicated treatment planning system.
This product was manually attached or bolted to the Linac head and then removed when not in use. A beam in the form of a rotating “slit” with the leaves continually changing position from on to off as and when required was delivered in an early “Tomotherapy” treatment format using individual pencil beams.
However, the point of this blog is not to discuss MLC and IMRT development but to look at unwanted exposure to lead.
So what other things out there might contain and expose us to lead?
I did some homework and this is what I came up with aside from leaded petrol fumes or living close to main roads:
Paint – Lead used to be added to paint, both in what we use to paint our houses inside and out and also the paint that was used in offices, schools and industrial buildings. The use of lead-based paints for homes, children’s toys and household furniture was banned in the USA in 1978. However, lead-based paint is still on walls and woodwork in many older homes and buildings.
Household dust, water pipes and contaminated water, imported canned food, foreign toys, traditional/herbal/holistic style medicines, soil, pottery, ceramics, china or crystal, eyeliner and lipstick, venison and other wild game that has been shot and lastly vehicle batteries and other battery types.
Many workers in construction are potentially exposed to lead, primarily as a result of the production, use, maintenance, recycling and disposal of lead material and products. Exposure also occurs during renovation or demolition of structures painted with lead paint.
And so in Radiotherapy, where are we today with regards to exposure to toxic heavy metals?
Are DCR therapy radiographers sitting on a potential dementia time-bomb due to previous lead exposure, similar to the heading of footballs?
This might be something that the Society of Radiographers wish to look at and perform some kind of ongoing survey over the next 25 years to see if there are any anomalies with regards to dementia and therapy radiographers and I for one would support it.
After all, the Scottish FA have just announced an upcoming ban on children under 12 heading footballs after the many years of dedicated work that England footballer Jeff Astle’s family have undertaken to establish the link between this activity within football and dementia. The link below contains much more information on Jeff Astle, his dementia and its causes. He played football most famously for West Bromwich Albion and also England in the 60’s and 70’s where heading a heavy wet football was a hazard that no one had really thought about.
Read more on the Scottish FA proposals and dementia: https://www.bbc.co.uk/news/uk-scotland-51129653
It was stated initially that Jeff Astle died in 2002 from an “Industrial Disease” but we know now it was the exposure to heading footballs that caused his dementia and has now been linked to many other players from the past. We did not see this coming in football and perhaps we may have missed this in radiotherapy so I for one would be happy to be tested in relation to lead exposure in my career and await feedback from the Society if they want to follow this up.
Duncan Hynd – February 2020