Brain cancer after CT examinations of children and young adults.
The use of CT imaging for orthodontic patients is an area of controversy and concern because of radiation exposure. I have posted about this before and suggested that we must be cautious using CT images. This new paper reported the results of a study looking at the incidence of brain cancer in children who had undergone CT examinations. The results were concerning.
In their literature review, the authors pointed out that the use of CT imaging is increasing, and there is a suggestion that many of these examinations are unnecessary. Notably, the head is the most frequently examined body part of paediatric patients. Furthermore, several epidemiological studies show increased brain tumour risk after paediatric CT examinations.
A high profile multinational team from Europe did this study. The Lancet Oncology journal publishes the paper.This is a world leading clinical oncology research journal with an Impact Factor of 54.
Lancet Oncol 2023; 24: 45–53. https://doi.org/10.1016/ S1470-2045(22)00655-6
What did they ask?
They did the study to
“Assess the risk of brain cancer following paediatric CT imaging”.
What did they do?
They did a cohort study using data from an extensive multi-national prospective registry. This was the EPI-CT study, a large European cohort of children and young adults exposed to radiation during CT examinations.
The team pooled data from Belgium, Denmark, France, Germany, the Netherlands, Norway, Spain, Sweden and the UK. First, they identified people who had at least one CT examination between 1977 and 2014. Then they linked the individuals with national or regional cancer registries. Individuals were included if they were alive at least one year after the first documented CT examination. They also had brain tumours according to the WHO International Disease Classification.
They also calculated the number of head and neck CT examinations and associated cumulative brain dose and fitted this into their statistical models.
The study’s primary outcome was the first reported brain cancer diagnosis after an exclusion period of 5 years after the first CT examination.
Their data analysis was extensive and complex. The most important factors that they calculated were the Relative Risk and the Excess Relative Risk.
What did they find?
They identified 658,752 individuals who were eligible for the study. 56% of these were male. After a median follow-up of 5.6 years, 163 brain cancers had occurred. Importantly, they detected a significant linear dose-response for all brain cancers. The Excess Relative Risk per 100mGy mGy was 1.27 (95% CI= 0.51-2.69). The Excess Absolute risk per 38 mGy was 1.1 (95% CI 0.6-1.6).
This means that for every 10,000 people who received a single head CT examination, approximately one person is expected to develop brain cancer attributable to radiation exposure.
Explanation of radiation dosage
We may not be familiar with the mGy as a unit of radiation. This represents the absorbed dose This is the energy concentration deposited in tissue due to exposure to ionising radiation. For diagnostic radiation, the equivalent dose is millisievert (mSv). Because all radiation used in diagnostic medicine has the same low-harm potential, the absorbed dose and the equivalent dose are numerically the same. Only the units are different.
I have found radiation doses rather confusing, but I found this web source that explains it well. I also found it useful to see the dose of various images and this site suggested that a dental Cone Beam CT had a dose of 0.18mSv.
Their overall conclusions were
“The significant dose-response relationship between CT-related radiation exposure and brain cancer emphasises careful justification of paediatric CT use”.
What did I think?
These findings are controversial. I will start with an explanation of some of the concepts that were discussed in this paper.
Firstly, when considering radiation exposure, we must assume that any dose above zero can increase the risk of radiation-induced cancer. In this respect, the results of this study mirror other studies on the no-threshold model for cancer risk from low-dose exposure. Importantly, the authors found that for every 10,000 people who received exposure, one person is expected to develop brain cancer. We cannot simply “brush off” this finding.
Some proponents of irradiating children for “their records “ will contend that the dosages recorded in this study were high. They certainly, seem to be higher than the average orthodontic CBCT. However, we must also remember several basic facts I mentioned in a previous blog post. These are:
- No exposure to X-ray radiation is completely clear of risk. All ionising radiation has the potential to cause harm.
- These are stochastic events where the magnitude of the risk, though not the severity of the effect, is proportional to the radiation dose. This makes the distinction between safe and dangerous exposure to radiation impossible.
- As a result, the justification for radiation exposure is that we do more good than harm. Therefore, radiation doses should be kept low, and all exposures should be minimised and in the patient’s best interest.
So, while we can argue about doses and the need for information, we must consider this study’s findings. In my view, these are stark. There is a link between head and neck radiation exposure and brain cancer. As a result, we must consider whether we can justify the routine use of pre-treatment orthodontic CBCTs when most information is available from a clinical examination and lower-dose traditional radiographs? It is even more difficult to justify taking post-treatment CBCT when we have removed appliances to satisfy our curiosity about root paralleling?
The consideration of this issue is long overdue.
Emeritus Professor of Orthodontics, University of Manchester, UK.