Work-Related Injury: Is Radiation to Blame for Cancer?
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Work-Related Injury: Is Radiation to Blame for Cancer?

By Dr. Zoomie

Dear Dr. Zoomie – I have a friend with cancer and he thinks it’s from working with radiation. His employer (of course) says that’s not the case – is there a way to tell who’s right? Thanks!

Wow – first, I’m sorry to hear about your friend. Between family and friends I’ve known far too many cancer patients – luckily, most have survived their illness and gone on to live for many years. But this is about your friend, so let me tell you how I’d look at this as a health physicist.

When it comes to trying to figure out if radiation exposure might have caused a cancer there are a few things I always try to keep in mind. One is that it is utterly essential to try to figure out what the radiation dose was – not to the person, but to the part of the person that got the cancer. If I get skin cancer on my lower right leg, the dose showing on the dosimeter clipped to my pocket doesn’t matter – the only dose that matters is the dose to the skin of my lower right leg (that being said, a dosimeter gives a starting point that can be used to determine dose to the right leg). Dose to my left leg, my abdomen, the bone of my lower right leg…none of that matters because that’s not where the cancer formed. The only dose that matters is the dose to the place where the cancer formed, and if I didn’t have a dosimeter at that location then I need to find a way to calculate the dose to that location.

The second thing that comes to mind is that cancer is not a rare disease. Depending on a country’s life expectancy over half of the citizens might develop cancer and as many as a third might die of it. Interestingly, this is a good thing – cancer is largely a disease of people who are old or elderly; the nations with the highest cancer incidence and mortality rates tend to be the nations with the longest-lived citizens. Nations with the highest cancer rates tend to have low rates of childhood mortality, low rates of infectious disease, low levels of occupational illness and injury – the nations in which people live long enough to develop the diseases of older age. The problem with this is that it makes it hard to determine if a person’s cancer was caused by their occupational radiation exposure or if it would have occurred regardless of radiation exposure.

What this means is that, to determine if your friend’s cancer is work-related, we first need to determine radiation exposure at the point of the cancer from the radiation source your friend was using and then to determine if that dose was high enough to have caused the cancer. And that frequently means going back to first principles – calculating the radiation exposure from a source of known strength using the principles of time, distance, and shielding to calculate the amount of radiation exposure to the site of your friend’s tumor. If the tumor is buried 2 inches inside the body then there’s two inches of tissue attenuating the radiation it received. If the tumor is on the opposite side of the body from the radiation source then we need to calculate how the dose was attenuated by the distance from the source. And if your friend only used (or carried) the source 10% of the time then they can only calculate the exposure based on 200 hours of exposure annually. This is the physics of the situation, and the physics aren’t amenable to wishful thinking, needing to pay medical bills, or any other factors that are so important to most of us.

So what your friend (or their lawyer) ought to consider is finding a radiation safety professional who can calculate the radiation exposure to the site of their tumor from the radioactive source that they were exposed to. But that’s just the first step – the second step is to determine how likely it is that this exposure might have caused that particular cancer. Some tissues are more sensitive to radiation and some are less. A dose to the thyroid is more likely to cause cancer than the same dose to the brain because the thyroid is more sensitive to radiation than is the brain.

Another factor includes the age of your friend when they developed cancer – the older they were, the more likely it is that the cancer was going to occur anyhow because cancer is primarily a disease of older people. And the amount of time between the radiation exposure and the cancer appearing important as well – it takes time for a cancer to appear, so a cancer that appears in just a few years isn’t likely to have been caused by radiation exposure while a cancer that shows up after a few decades might have been. There’s a nice program called IREP (Interactive RadioEpidemiological Program – that can help with this part. And I really need to emphasize this part – this will be a lot more convincing if it’s done by a radiation safety professional.

What I normally do with this sort of thing is to start by looking for radiation dosimetry or survey records – if the worker had a dosimeter than I use those numbers. Otherwise I begin by calculating the worst-case – what’s the highest dose the site of the tumor might have received, then plug those numbers into IREP to see how likely it is that the highest possible radiation exposure might have caused the cancer. If it turns out that this deliberately high estimate is unlikely to have caused the cancer then it makes me realize that the probability will only drop as the calculations become more accurate. On the other hand, if this first guess leads to a probability of causation (POC) that’s fairly high (over 50%) then I know that my work is just starting and I need to do more work to come up with the most accurate dose estimate I can develop.

What that means in practice is that I might start off assuming that the worker was working a few feet away from the source, was exposed to it 24/7/365 (which comes out to 8760 hours annually), and that there was no shielding between the source and the site of the tumor. If this calculation shows that the POC was, say, 10% then I can pretty much stop there and write up my report saying that under the most conservative assumptions there’s a 90% probability that their cancer had nothing to do with their occupational radiation exposure. On the other hand, if the POC comes out at 70% under these conditions then I need to refine my assumptions. I’d start by assuming that the worker, instead of living with the source continuously, only spent every working hour with it (about 2000 hours annually). If the POC is still higher than 50% then I’ll go through work records to determine the actual number of days the worker had worked with the source and, if necessary, will start to look at other factors about which I’d made simplifying assumptions.

If, after all of this, it gets to the point that I think my calculations are as accurate as possible and the POC still comes out higher than 50% then I accept that the cancer is “as likely as not to have been caused by occupational radiation exposure.” With a POC higher than 50%, the worker’s cancer was probably caused by occupational radiation exposure; if the POC is lower than 50% then it most likely was not.

And that’s the process – rather than arguing about who’s responsible, take the time to do the work to find out. Look at dosimetry and/or radiation survey records, calculate radiation exposure, determine the POC, and refine the dose and POC calculations as necessary. In favor of this approach is that it’s based on something other than conjecture or wishful thinking; unfortunately, it takes time and, if you need to hire a consultant, it’s not cheap. But at least at the end of the process there’s a solid scientific justification for the assignment of blame – wherever that blame falls.