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Health effects of radiation exposure
Joanne Shaw discusses the various health effects which can be caused by radiation exposure and compares these effects to other sources of radiation.
We’re going to look in a bit more detail, now, at the health effects of radiation exposure. You’ve already learned that X-rays carry energy, enough energy to cause ionisation, and break chemical bonds in the molecules that make up human cells.
X-rays were first discovered by Wilhelm Rontgen in 1895. And their potential in medical diagnosis was quickly realised and put to use. This image claims to be Rontgen using an early X-ray set for medical diagnosis.
And this image, titled Hand with Rings, is a print of one of the first X-ray photographs, showing the left hand of Rontgen’s wife, Anna Bertha Ludwig, in 1895. Soon, X-rays were in widespread use, but with no knowledge of their detrimental effects, there was little regard for radiation protection. Here we can see a photograph from the late 19th or early 20th century of a Roentgen therapy suite in a London hospital. If you look closely, you will see that there is no shielding at all on the glass X-ray tubes.
It was not long before the first harmful effects of radiation exposure were observed. This image shows the right hand of a pioneer radiologist. The first injury was seen in 1899, four years after the discovery of X-rays. This radiologist’s hand was amputated in 1932, and death from cancer occurred in 1933. We’ve already seen in the article X-ray hazards, that X-rays are capable of causing ionisation and breaking chemical bonds in human cells. The effect of this damage on a cell depends on many things. The type of cell, for example, some tissues like skin, are more susceptible to radiation damage than other tissues, like brain and muscle. The rate at which radiation exposure is received is another factor that affects the outcome.
A radiation dose of say, 1,000 millisieverts, received in a few minutes will be more damaging than the same dose received over a lifetime. But, in general, the higher the exposure, the more serious the damage to the cell, as shown in this image.
So we’ve seen that, depending on the level of ionisation damage, the cell may die, or its functions may be affected. Damage caused by ionisation at the cellular level may also lead to detrimental health effects, which we can divide into two groups. The first group is known as tissue reactions, and these health effects only appear when a threshold level of radiation dose has been exceeded. Once that threshold has been exceeded, the effect is certain to appear, usually within a few days of the radiation exposure. And the severity of the effect is proportional to the size of the radiation dose.
Here, we see a photo of an injury to the skin of the forearm that appeared a few days after a highly localised exposure from a narrow beam of x-radiation while aligning a laboratory analyzer.
The first picture shows the initial reddening, and the second shows the subsequent blistering. You’ll note, however, that the thresholds for these tissue reactions are very high doses. Users of dental X-ray equipment will not receive doses of this magnitude, unless there is a serious failure of a safety system, or a safe working procedure.
Here are the threshold doses for tissue reactions following a whole body radiation exposure. Again, you will note that the thresholds are much higher than the radiation doses received during routine work with dental X-ray equipment. The image here shows damage to chromosomes following a radiation exposure.
The second group of radiation health effects includes radiation-induced cancer. We do not yet have much reliable data on this health effect at the low exposure levels seen in dental practice. What data we do have, comes from studies of highly exposed groups, such as the survivors of the atomic bombs in Hiroshima and Nagasaki at the end of the Second World War, and the mid-twentieth century radium luminizing workers. Observations made during studies of these groups led to the following assumptions. The risk of radiation-induced cancer is directly proportional to the radiation dose received. There is no threshold below which radiation-induced cancer does not occur.
In other words, even a very small radiation dose carries a very small risk, and radiation-induced cancer may appear many years after exposure.
Research carried out by the International Commission on Radiation Protection, ICRP, indicates that the risk of fatal cancer arising directly from radiation exposure is approximately 4%, or 4 in every 100, for every sievert radiation dose received. As mentioned before, 1 sievert is a very large radiation dose. If we extrapolate that risk factor down to the level of doses that we might receive during work with X-ray generators, this implies a risk of fatal cancer of 1 in 25,000 for a single 1 millisieverts radiation dose. These values apply to a working age population, aged 18 to 65 years, and the risks for younger people are higher.
That’s why it’s particularly important to ensure that the radiation exposure of paediatric patients is properly restricted, including during dental radiography.
Let’s try and visualise that risk. This image represents 25,000 people. This is a convenient number to use, as it is roughly the number of registered radiation workers in the UK.
The Cancer Research UK website indicates that in 2017, cancer was cited as the cause of death in 28% of UK deaths. If we assume that this number stays the same in future, we would expect that about 28% of our 25,000 people will die of cancer at some point. That means about 7,000 cancer deaths in the population shown. These are represented by the people shaded in red. Note that the likelihood that any individual will develop cancer at any time is affected by factors including genetics, lifestyle choices, and their environment.
Now imagine a scenario whereby all 25,000 people are exposed to a lifetime radiation dose of 1 sievert, or 1,000 millisieverts. For example, let’s say they receive a radiation dose of 20 millisieverts every year, for a full 50-year career. As a consequence of this exposure, we would expect to see about 4% of the population of 25,000 develop fatal cancer as a direct result of this radiation exposure. That’s an additional 1,000 people. These are shown in yellow above.
Note again, that it is very difficult to isolate the cause of an individual’s cancer, even at this high dose. Environmental, genetic, and lifestyle factors are still bigger contributors to the risk than the radiation exposure.
What if the lifetime dose to the population is much smaller, say 50 millisieverts, instead of 1,000? This represents a dose of 1 millisieverts per year, for a 50-year career. In this case, we expect to see only an extra 50 cancer deaths in the population, against a background of about 7,000 deaths. These extra deaths are shown shaded in green in our picture.
So, if we can reduce the lifetime worker dose from 1,000 millisieverts to 50 millisieverts, a significant number of cancer deaths will be avoided in the population. The lower the dose, the smaller the risk of developing a radiation-induced fatal cancer.
It can be helpful to put potential radiation doses from dental radiography in perspective by comparing them with other radiation exposures that we receive in day-to-day life, and with other risks.
This pie chart illustrates the average annual radiation dose to a UK citizen, and what that is made up of. The average annual radiation dose in other countries varies, but the makeup of that dose is similar. You’ll see that most of our annual radiation exposure is from natural sources, such as radon gas. This can be a useful comparison when putting the small effective doses received by patients and staff during dental radiography into perspective.
Let’s look at the typical effective doses to patients from a range of common dental X-ray examinations. A dental radiograph can deliver a radiation dose of a few millisieverts to the area under examination, but for comparison with other risks, it makes more sense to consider the effective dose. Effective dose is calculated by taking the radiation dose delivered to the area under examination, and then using standard tissue weighting factors to work out the effective whole body dose. You’ll see that for each type of radiograph, the effective doses cover a range. This is due to design differences in the X-ray equipment, and in the speeds of the imaging systems being used.
And for comparison, here we see the range of effective doses received from other medical examinations, and in other areas of life. Although I imagine not many of you will have been to the International Space Station, the effective dose received by astronauts on the ISS, and by aeroplane travellers closer to Earth, is due to cosmic radiation, high-energy ionising radiation originating from outer space.
We can also use the risk factors mentioned earlier to compare the risk from a radiation exposure directly with other risks. Of all the activities listed, receiving a single radiation dose of 1 millisievert is the least likely to cause death.
To sum up, then. X-rays are a form of ionising radiation, and exposure to ionising radiation can result in detrimental health effects. These health effects fall into two groups. Tissue effects, such as burns and hair loss, which occur soon after exposure and do not appear, unless a very high dose of radiation has been received. And longer term effects, such as radiation-induced cancer, which can occur many years after exposure, and for which there is no safe threshold. We have seen the range of radiation doses that we might receive at work, and put these into perspective by comparing these to the radiation exposure we might receive in other areas of life, and comparing to other risks.
Provided sensible steps are taken to restrict radiation exposure, as described later in this course, these risks are very low.
We will now investigate the health effects which can be caused by radiation exposure.
The video starts looking at the first uses of X-ray sets and the initial disregard for the potential harmful effects. Cell damage from radiation is covered and the potential resulting health effects. These health effects are divided into two subcategories – tissue reactions and radiation induced cancer – and both are explored further in this video. Potential radiation doses from dental radiography are then put into perspective against other radiation exposures in daily life.
A PDF version of these slides is available in the downloads section below.
Dental professionals aren’t the only ones that may have to work with radiation, can you think of any other settings where a professional or a member of the public may face exposure? Let us know in the comments.
This article is from the online course:
Dental Radiography: Radiation Protection in Dental Practice
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Dental Radiography: Radiation Protection in Dental Practice
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