I was recently delighted to receive a phone call from the Scottish health services for a PET scan. That might seem a strange thing to be pleased about, but I have been feeling helpless in the face of a dangerous problem called ‘radiophobia’, and this was a breakthrough. I am in the fortunate position of working at a university where I have access to people who understand these things, so here I’m writing down why radiophobia is wrong, and how it causes many people to miss out on potentially life-saving healthcare.

I first met radiophobia when a medical person told me “you don’t need a PET scan, and we limit the number of scans people have, because we don’t want to cause more problems than we find”. I had been enquiring after a PET scan because it is a high-resolution picture and the given reason rang alarm bells with me. But I wasn’t sure how to respond, and left it, while seeking advice about the fact. It’s hard to fight a system though.

Then, to my surprise, something changed and out of the blue I was offered a PET scan after all. The friendly voice on the phone reassured me “you will be a little radioactive after the scan…” so I responded “sure, like living in Aberdeen makes me radioactive!” because I now knew that was the comparison point. They laughed in understanding, and that was that.

But later I received an official pre-scan booklet from NHS Scotland containing scary advice such as:

During the 4 hours after your scan you will need to follow these precautions:

• Avoid close contact with other people, such as hugging

• Avoid any contact with children or pregnant people - being at a distance of more than 1m away is fine.

After 4 hours has passed, you may return to all normal activities.

The scary vibes didn’t stop there. On arrival for my scan I was escorted to a little cell with radiation warnings on the door, and after being gently injected with the radioactive tracer Gallium-68, the staff shut me in. This could have been frightening, because nobody wants to be invisibly poisoned with something so fierce it will leap inside other people and hurt them. No wonder the health services want to limit radiation exposure - except, experts helped me understand, it is unscientific nonsense built into UK safety laws and medical standards.

Aberdeen is just fine

People in Aberdeen do not show signs of increased cancer, even though the kind of rocks the city made of give off radioactivity equivalent to a PET scan. Similarly, people arriving in Edinburgh from a flight in Australia have experienced higher than usual space radioactivity, because they have had 10km less atmosphere to protect them. And generations of people have lived in regions of Iran, China, India and Brazil with up to 30 times the radiation exposure of Aberdeen (or a PET scan), but detailed studies show these too have no greater chance of getting cancer.

This is about asking the right question.

Radioactivity can surely be dangerous, and it is thought that 100 years ago its discoverer, Marie Curie, died from extreme medical X-Ray exposure. Nothing like this would ever be considered today, but you might think the question should be What is a non-extreme dose? How much causes harm?

The reason this question is not asked starts with Hermann Muller’s 1946 Nobel Prize lecture, in which he described giving fruit flies very high doses of radiation (they didn’t like it) and then claimed any dose at all of radiation causes genetic damage. Ever since, when it comes to radioactivity safety, the following incorrect question is asked: Given that any dose causes harm, how much harm does this particular dose cause?

A lot of science papers have debunked this question, making the case that the true risk is misdiagnoses due to phobia-driven lack of scans. Here in the UK, legislation mandates a maximum dose of 7 PET scans per year, despite there being no evidence of harm to millions of people who live with 4x that amount for decades. The UK legislation appears to rely in part on the BEIR VII report which states there is a 1 in 136 risk of cancer from being exposed to 1/3 of one PET scan’s worth of radiation. That seems significant, until it becomes clear this is based on assumptions dating to at least 1958. At no point has there been confirmed evidence to support this claim, which puts into the class of mythology. Unfortunately it is very convenient for administration to have a neat rule like this, so it persists in regulations worldwide.

Radiophobia directly causes other harms, including:

Cells cope because damage is normal

Every cell in our bodies sustains many thousands of DNA damage events every day caused by the business of being alive, and we have continuous molecular repair systems to deal with this. A PET scan delivers approximately 7 millisieverts of radiation, where a millisievert (mSv) is the unit for how much radiation the human body absorbs, typically from cosmic rays zipping through us, and radiated out of rocks, food, and the air. Given I live in Scotland but not in Aberdeen, I receive about 2.7 mSv per year. At 7 mSv, the additional DNA damage from the PET scan amounts to roughly one extra DNA break per cell, which is far too low to be measured or to be worried about.

There is an obvious objection: the scan happens in an hour, and if I had my annual dose of say, salt, in an hour I would die! That is about capacity. My kidneys don’t have the capacity to clear that much salt and so they choke, but our DNA repair capacity doesn’t start to get overloaded until at least hundreds of mSv, and nowhere near 7 mSv.

So what to do?

For myself, I’m very glad to have had one scan I thought I would not.

For others, be aware that the radiophobia starts long before the doctor says ’no’. The scary misinformation trains people to just nod along, so perhaps it is worth enquiring closely by default: why am I not having a scan, is it due to dosage concerns and minimising radiation exposure?

Starting points for further investigation: