Q&A With Dr Emma
Hi Dr Emma, I have booked an appointment with my dentist to get dental x-rays completed but I’m worried about the exposure to radiation. How safe are dental x-rays? Regards, Michelle - Waterford (WA).
To this day, I still remember my year 11 physics teacher saying that radiation is the only thing he's truly scared of. It's not just invisible, it's undetectable by all the human senses. It's potentially deadly, both acutely and in the long-term in the form of cancer.
It's not all bad news though. There are different types of radiation, and the one we should be worried about is ionising radiation. This is radiation which has enough energy to interact and mess directly with our atoms, which make up the molecules, which make up the cells, which make up our bodies. Things like radio waves, microwaves, infra-red light ("night vision"), electric fields, magnetic fields, visible light, and sometimes ultraviolet light are all forms of non-ionising radiation. They don't have enough energy to cause damage under normal circumstances. X-rays, gamma rays, cosmic rays, some ultraviolet light, and particulate radiation from materials like radon and plutonium, are all ionising. They all have the potential to damage the human body, but like a lot of things in life it is dose dependent. A pinch of salt on your dinner is not going to do any harm, but eat 5kg and you'll be in trouble. It's the same with ionising radiation, so working out what is a safe dose is really important.
Here's where it gets curly… radiation can be measured in lots of different ways. Just like distance is described in metres, when measuring radiation out in the world you might describe it in becquerels, joules, or roentgens. That's all very well from a scientific perspective, but when it comes to human health what we're really interested in is the dose that's being received. To make things really interesting, radiation dose can be measured in two ways:
- Grays (Gy), which measure the amount of radiation absorbed by the human body. This is useful because when it comes to bad health effects, only the amount absorbed by the body matters. Any radiation that bounces off or passes straight through will not cause damage. It's not the best measurement though, as different kinds of radiation cause different amounts of damage. Grays give you an idea of dose, which is useful when you're talking about acute effects like radiation poisoning. It's far less useful when trying to work out cancer risk over a lifetime.
- Sieverts (Sv) are the unit used to measure the effective dose of ionising radiation to the human body. It takes into account the type of radiation, and the type of body tissue, (bone, skin, brain etc.). The true way to measure your risk from exposure to radiation is in sieverts. If you're ever unfortunate enough to have to undergo radiation therapy, your doctors will portion out your treatment in sieverts.
Because we're always exposed to small, natural amounts of radiation from both the Earth and outer space, it's important to put things in perspective.
- 1Sv is a huge single dose, being potentially fatal if received all in one go. However, for an Australian it's the normal natural background radiation dose when spread out over 50 years.
- 100mSv, (1 tenth of a Sv), when received over the period of one year is the smallest dose clearly related to an increased cancer risk. Doses less than this do carry some risk, no amount of radiation is considered "safe", but 100mSv is the point at which there's a definite higher risk of cancer.
- 2mSv, (2 thousandths of a Sv), is the Australian normal yearly dose from natural background radiation.
- 16μSv, (16 millionths of a Sv), is an aeroplane flight from Perth to Darwin.
- 5μSv, (5 millionths of a Sv), is a dental radiograph, (commonly called an "x-ray).
- 0.1Sv, (1 ten millionth of a Sv), is the ionising radiation dose from eating one banana.
This means that statistically, to increase your risk of cancer you'd need around 20000 dental radiographs taken in a single year, (or eat 2740 bananas every day for a year). When you look at it like that, it's easy to see that dental radiographs carry an extremely low risk. The benefits to dental diagnosis and treatment vastly outweigh any risks from the radiation dose.