February 06, 2023

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.  

Brain cancer after radiation exposure from CT examinations of children and young adults: results from the EPI-CT cohort study.

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.
Final comments

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.

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Have your say!

  1. I like your conclusion ant your wisdom

  2. The CT technology assessed in this study is “old”, going as far back as 1977. These were medical CT scans, not Cone Beam CT (CBCT) scans. The available studies suggest that if the proper settings are used on the CBCT machine, the effective radiation dose is about 10% of the radiation of a medical CT scan for the same area, suggesting that CBCT scans have up to 90% less radiation exposure than older medical CT scans.

    • Yes, but we need to consider that there is no safe dose of radiation. I certainly would not agree to any of my children (when they were younger) having a CBCT for routine orthodontic treatment.

      • If the concern is “brain cancer” (which sounds more emotional than medical), then CBCTs might be safer since the FOV is (maximally) cranial base to the hyoid bone, avoiding or minimizing radiation of cerebral tissues.

        • Yes, but the main point is that there is a risk of tumour then we need to consider is the benefit from a CBCT worth that risk, particularly if it is a post-treatment CBCT? I also appreciate the effect of reducing the FOV, but it does not eliminate the risk.

          • By definition, you can’t eliminate a risk. In other words, when is a risk not a risk? When it’s a certainty. Seat belts don’t eliminate the risk – but here the principles of ALARA are being met, at least in my view.

          • Thanks for the reply. So to be clear, do you think that we should be taking pre and post treatment CBCTs on routine orthodontic patients?

          • Depends what you mean by “routine orthodontic patient”. The issue we’re addressing here is CT (or CBCT) as a risk factor in the incidence of brain tumors; and it would appear that a CBCT is unlikely to increase that risk. Presumably, that study’s dataset could be stratified on that basis to see if a tangible difference emerges?

          • Thanks Perhaps I did not make myself clear in the blog post. The issue I am addressing is that we need to be careful with any exposure that is not necessary. I am flagging up what appears to be a current trend of taking CBCT images on all patients when they are not needed and this dose is still likely to be higher thant 2D imaging. Or is not clear?

          • Kevin:
            You clearly say “we must consider this study’s findings”. When we do, we find they are of little relevance, if any, to orthodontic protocols. To re-iterate;
            1. They used old Medical CT scans unlike newer dental CBCT scans
            2. They scanned the entire head unlike CBCT scans that avoid the brain
            I believe your conclusion is non-sequitur because you’re conflating the two. A better approach might be to find retrospective Medical CTs and document the incidence of pediatric brain tumors. Next, compare that incidence to a database of pediatric orthodontic CBCTs. Let the data speak – otherwise it sounds a bit scaremongering.
            Disclosure: I have no relationship with any CBCT company

          • Thanks for the comments. i guess that we simply need to disagree on this. From the evidence that I have looked at I feel that the risk is not worth taking for the sake of post treatment images.

        • The The American Academy of Maxillo-facial radiologists’ position paper is still current (I was informed by one of the authors). Maybe they know a thing or two about dosage and use on younger patients. It is an informative read.
          The concern about radiation includes brain cancer, thyroid cancer and goitres and tissues of the eye. So this figure underestimates the total risk, just one risk. Also the cohort is likely to be older than many of our patients so our patients have a higher risk.
          When the position paper update suggests the radiation risks are equivalent to Ceph OPG I feel it will then be at a safer level for our patients until then you are suggesting greater knowledge than radiology specialists.

  3. What if the radiation dose of cbct is less than that of a 2d pan?

    • Your point is often made but can you let me know any CBCT that is less than the dose of a pan?

      • There are a few machines on the market that can take a cbct with a lower dose of radiation than a pan. The current machine I use can acquire a large enough volume to render both a pan and ceph with an effective dose of around 15 microsieverts.

      • Ludlow, John Barrett and Koivisto, Juha: Dosimetry of Orthodontic Diagnostic FOVs Using Low Dose CBCT protocol

        • Thanks for this. The reference you quoted was a poster at the IADR meeting. This represwtns a low level of evidence. The authors also received an honorarium from the makers of CBCT they tested.

          • I’m just curious…why would Ludlow/Koivistoand risk their reputations by publishing false and/or misleading information? Other manufacturers show similar doses as well (iCat for example). Another concern is that discussing orthodontic related low dose CBCT in the same vein as medical CT seems a lot like a “red herring” argument and is somewhat irresponsible. My biggest concern is that I don’t want to over-radiate my patients; and if I follow the recommendation of using 2D first, and then following with 3D if indicated would expose all my patients to more radiation now than they are currently receiving.

          • Thanks, I was only pointing out that they were conflicted and they did declare this. However, whenever a conflict is declared or detected we need to take this into consideration when we interpret the paper or research output. You are correct in pointing out that this paper was concerned with medical CTs and I drew attention to this in my paragraph on doses. I appreciate your feedback, but do you really take CBCTs on every patient in order to reduce the radiation dose on the few that need additional views. I only very rarely was unable to come to a treatment planning decision when using 2D radiographs when I was practicing and I worked in a tertiary referral hospital for children with complex medical problems. My main point is that we should not take “routine” CBCTs which is the current recommendation in most of the world, including the USA.

          • My main point is that using 2D in my office would be irresponsible and not adhering ALARA given that I have the ability to take CBCT at a lower dose than 2D At this point many manufacturers produce machines that can do the same. So, of course I routinely use 3D on all my patients even for progress records because I don’t want to use extra radiation with 2D to get less information.

            My concern is that there is significant lack of knowledge on the part of many orthodontists around the world and when they see a blog with this title by someone so respected within the profession that they might be influenced by simply the title and not understand that there is a difference between medical CT and CBCT.

            To me it seems like much of our profession is behind with regard to technological developments related to the use of CBCT in orthodontics. In addition, the ability to customize treatment based upon individual patient morphology instead of treating to cephalometric norms provides opportunities to provide better patient care.

            The argument of whether or not to use CBCT in orthodontics based upon radiation dose is a moot point given the lower dose ability of newer CBCT machines.

          • Thanks for replying. Before I get back to you tomorrow, it would be useful if you could let us know the make and doses of your CBCT machine. This would help our discussion.

          • From 2015 until 2021, I used the Planmeca Promax Mid (which is the same machine from the research poster by Ludlow/Koivisto). I currently use the Planmeca Viso G7. I am also a part-time assistant professor in the residency orthodontic program at University of Tennessee where we currently use the Planmeca Promax Mid.

            For full disclosure, I am a KOL for Planmeca because I want other orthodontists to know that they can treat patients with less radiation and more information by using CBCT (my message, not theirs). I’m sure they would love to sell more machines…I can’t say that I’m overly worried about that. My main concern is that patients receive the highest standard of care possible. My hope is that by using CBCT it allows me to better adhere to the ALARA principle while also giving me significantly more information with which to make decisions about treatment.

          • Thanks for the reply. Yes, you are correct, if you believe that you are complying with ALARA and using routine CBCT then this is your clinical decision.But I was very interested in the comment from Marian Wolford on this thread.

  4. Routine use of pre-treatment orthodontic CBCTs can never be justified. You must have a very specific clinical problem area where CBCTs scans can make a real difference in the caretaking of the patient. In most cases, even if we are talking about impacted teeth, conventional low dose radiographs will be sufficient for a well-considered diagnose/treatment plan. Only in cases where we have impacted teeth in complex positions or if we fear significant damage on teeth/roots due to impacted teeth or other pathological findings it can be justified to use pre-treatment CBCT scans. I have great difficulties to see any justification of post-treatment CBCTs in orthodontics. Why should we expose an adolescent to radiation when we have finished our treatment. What are the benefits for the patient other than an increased risk due to unnecessary radiation.

  5. Routine use of CBCT would help orthodontic diagnosis how exactly?
    Zero benefit, and the radiation increase makes this technology beneficial only in cases requiring a 3D view (impacted canines, asymmetry being treated surgically etc).
    Additionally, all these images need to be evaluated by a radiologist, since most Orthos are unfamiliar with a thorough CBCT eval to indentify pathology etc. So, unless one is doing that, there is the added liability as well.

  6. Hey Kevin,

    Thanks for the blog post.

    Just to be clear, from your conclusion: “most information is available from a clinical examination and lower-dose traditional radiographs”

    Are you suggesting that it is permissible to take pre treatment radiographs as long as they’re lower dose than CT? How much lower would qualify?

    When you say no radiation dose is completely free of risk, how much dose is ok vs not ok in your view?

    If newer CT machines could come close to a lat ceph/pan radiation, how close in numerical value would you suggest to qualify it for use?

    In more precise language, when you say balance the risk, what do you mean exactly? Is there a number cut off? Obviously this would differ per patient but how do you determine this?

    Are you advocating for ALARA where you are saying choose the lowest dose that gets you the minimum information to carry out treatment? And if so, if we hypothetically took a CT, how close to the dose of lat ceph pan would you think is acceptable?

    Thanks for the consideration

    • Thanks for the comments. In answer to your questions.

      I am suggesting that we should take any image only when necessary. This is a reflection of the BOS guidelines that are pretty clear on this. For example, in a Class II mild crowding case it may not be necessary to take a ceph, if this is not going to change your decision.

      The development of low dose CBCT imaging will be a major benefit.

      Yes, balancing the risk depends on the features of the patient. For example, if I were to plan a functional appliance treatment I would want a ceph so that I can see the position of the lower incisors, to make sure that I do not procline them too much. Again a clinical decision.

      Yes, I am advocating ALARA. I am not sure that I can answer your last point, as we do not accurately know the dose of some of the new low dose machines.

  7. Absolutely agree with Ken and Kevin on this matter, routine use of CBCT in orthodontic treatment cannot be justified even if there is a really small chance of an iatrogenic induced medical condition such as brain cancer! More research needs to be undertaken to be absolutely certain, there can be no ifs and but once the damage is done.

  8. CBCT allows one to visualise the alveolar bone. Knowledge of the state of the alveolar bone is fundamental to orthodontic diagnosis and treatment planning. You will make your extraction/non-extraction decisions with knowledge rather than a guess. CBCT also allows visualisation of root position in three dimensions which is fundamental to optimum orthodontic finishing. You will know with certainty whether your case is finished adequately or not.

    If these benefits are available at less radiation dosage than conventional 2D radiography, then we as a profession must discuss whether CBCT for records and pre-finishing becomes the proper standard of care.

    Once we have decided to take some risk with radiographic investigation of our patients for their benefit, maximising the information we get for the risk is common sense. As a profession, pursuing whether the low dose CBCT technology really is lower dose that 2D radiography is very much in the best interests of our patients.

    • I agree that we need to check the dose and see if we can reduce it for CBCT. However, as things stand the dosages are not completely clear and therefore we need to be more cautious. I certainly do not need a CBCT on all my patients. But I wonder if that is a reflection of clinical experience?

  9. I would encourage everyone in the U.S. using CBCT units to purchase a copy of the NCRP Report No. 177 from the National Council on Radiation Protection and Measurements ($80) entitled “Radiation Protection in Dentistry and Oral & Maxillofacial Imaging”. It has replaced Report No.145 (2003) and has updated recommendations. Of particular interest is recommendation #55 listed in the executive summary. It states, “Cone-beam computed tomography (CBCT) examinations shall not be used as the primary or initial imaging modality when a lower dose alternative is adequate for the clinical purpose and shall not be used for routine or serial orthodontic imaging”. There are 62 recommendations in the executive summary with 9 referencing CBCT machines.

    • HI Marian, this is a very useful comment and is the same as the recommendations produced by the British Orthodontic Society. I am also aware of some US orthodontic practices where the person who orders the imaging is not the orthodontist but a treatment co-ordinator. This clearly flies in the faces of all recommendations?

      • What if CBCT is the lowest dose imaging modality? Also, the orthodontist should always be the one ordering the imaging. No one else in the office is qualified to do so; This would obviously be negligence on their part. I really don’t understand why the push back to CBCT given the lower dose consideration. At this point one could argue lack of training or something like that, but not dose. I’m really confused by anyone wouldn’t want more information with less radiation.

        • I agree more information from less radiation is a goal that we should aim and hope for. But we need to be clear on whether the dose of a CBCT is less than a pan and ceph. To date I am not aware of any good publication that states this is the case. If you can point me in the direction of a published peer reviewed paper, I will review and publicise it.

  10. Thanks Kevin, another area of our specialty with diverse opinion as noted above. I was recently on a panel at the Saudi Orthodontic Clear Aligner Conference discussing CBCT use in orthodontics, with the main platform being the integration of CBCT into computer programmed aligner software programs. This technology forces us to consider/ reconsider and justify our diagnostic records, particularly as it is used as a marketing spin for some products. (I am trying to keep this generic). The panel included a wonderful specialist in maxillo-facial radiation – Dr Dani Tamimi. (Harvard educated and US based). Not only did I learn much from listening to her lecture, and insight on the panel , I later attended an on-line course that she provides via Beamreaders.com. It was really refreshing to have a practicing specialist from another field (not an orthodontist with an interest in CBCT) present, particularly when we are obligated to learn more about this technology and how it may impact our patients. (Another controversial area she discusses is airways…not sure I fully concur here, but always good to hear differing opinions especially with clinical examples) Whilst the younger gen are no doubt integrating comprehensive CBCT education into ortho curricula (including the obligatory interpretation); as a more “mature” member of our specialty, I enjoyed the learning opportunity, as I enjoyed learning from the likes of David Hatcher in the past. I would encourage conference organizers to invite specialists in this field.
    *VV – presents some lectures sponsored by Align Technology

  11. Sir,

    I read with interest the blog along with all the comments to the blog. My take home message –

    First and foremost, don’t use CBCT except as an additional special Investigation for a localised examination, where indicated, in Orthodontics.

    Last but not the least, stay away from post-treatment CBCT as a “routine” protecting-yourself exercise in Orthodontics except when you are treating your own children. If the risk is ‘really low’ then using it on our own children should be the only thing we should be doing for the next generation or two until enough data has been collected to end the controversy once and for all.

    What is a clinician without human emotion? I guess ChatGPT. When we remove emotional response from the equation, we remove ‘care’ from healthcare.

    Thank you for your selflessness.

    Yours sincerely,

    Karun Sagar
    Disclosure: I have never ordered/interpreted a CBCT scan, it is beyond my current level of training.

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