January 22, 2024

Exposure to Head and neck CT radiation is associated with blood cancers.

About a year ago, I did a post on the incidence of brain cancer after CT examinations of children and young adults. This was a very controversial blog post, and there were many comments. Most of these supported the research, and others attempted to minimise the concerns raised by this paper. The study team have now published a further paper from this study. This addresses the incidence of blood cancers following CT radiation scans of children and young adults.

Before I get into this paper, I would like to highlight that the authors pointed out.

“There is no dose threshold below which the risk of radiation induced cancer is zero”.

What did they ask?

They did this study to answer this question:

“What is the risk of hematoligical malignancies in relation to radiation exposure from CT examinations in childhood, adolescence, and early adulthood”.

It is clear that this is a very relevant question to all those practicing orthodontics.

What did they do?

This paper was one of the outputs for the EPI-CT study that includes data from 948,174 people from 9 European countries. The analysis includes data from 876,771 participants who underwent 1.3 million CT examinations. The team followed them up for at least two years following their first CT.

The team estimated radiation doses to the active bone marrow according to the body part scanned. Then they obtained data on 790 hematological malignancies. At the next stage they used complex modelling techniques to take into the account of confounding variables to calculate the relative risk of haematological malignancies following the CT scans.

At this point, I would like to remind readers that the relative risk (RR) or risk ratio is the ratio of the probability of an outcome in an exposed group to the probability of an outcome in an unexposed group.

What did they find?

The mean cumulative active bone marrow dose was 15.6 mGy in the whole cohort and 13.0 GmY in the cases. Importantly, they found increased risk for haematological malignancies across all the dose categories.

The excess relative risk per 100 mGy was 1.96 (95% CI=1.1-3.12).

These results suggest that for every 10,000 children examined with a CT (mean dose 8 mGY) 1-2 of them are expected to develop a haematological malignancy attributable to the radiation exposure in the subsequent 12 years.

What did they conclude?

Their overall conclusion was:

 “There was a consistent and robust dose-related increased risk of radiation-induced haematological malignancies”

What did I think?

This was another paper that highlighted the risk of CT scans to children. In this respect, it is important and we cannot simply ignore the findings. However, I did find some aspects of this research a little difficult to fully understand. So, I asked my collegue Keith Horner to explain things to me. Keith is Emeritus Professor of Oral and Maxillofacial Imaging, at the University of Manchester. He was also the co-ordinator of the SEDENTEXT project and an author of the British Orthodontic Society Orthodontic Radiography Guidelines. This is what he explained to me.

Keith’s Comments

“In this study, the scans were CT examinations and not CBCT. However, it is possible that the sample included some CBCT scans, as the classification depends on the hospital’s coding system. The study found that the cumulative doses were not evenly distributed, with a mean dose estimate of approximately 15mGy and a median of 10mGy. This represents an average of 1.5 scans per individual over the study period. Therefore, we could roughly estimate that the mean dose per scan was about 10mGy, and the median dose was approximately 7mGy. Most scans were of the head, so considering the study results in an orthodontic context is fair.

When we consider the possible CBCT scan doses to bone marrow (as opposed to CT). Ludlow et al. reported on this (2015;https://pubmed.ncbi.nlm.nih.gov/25224586/). They found enormous dose variations according to the particular manufacturer and model of the CBCT machine. However, they calculated that the mean bone marrow dose for a 10-year-old child for a single scan with “large” or medium-sized fields of view was 0.13mGy (+/- 0.08mGy sd).  For small fields of view scans, they were 0.06 mGy (+/- 0.05mGy s.d.).

Paradoxically, for adults who have less active bone marrow, the doses were higher, which might be because more studies were available to include. Rather than quibbling over fractions of mGy, it’s reasonable to say that the CBCT bone marrow doses might be roughly in the range of 1-4% of those for CT.

We can conclude from this study that using a CT or CBCT scan does seem to carry a small risk of malignancy in irradiated organs and tissues. The risk is highest in children and in females. Some might argue that the risk is negligible, but the benefit must be considered.  Most of the CT examinations in the epidemiological study would have been done for serious things – trauma, suspected or established intracranial pathosis, etc., some of which might have been life-threatening”.

My comments

I have given the paper and Keith’s comments a lot of thought. My feeling is that even though the risks maybe small. We need to consider the benefits of taking a CBCT. I am now going to be a bit controversial and blunt. I have published several posts on the research into the use of CBCT in orthodontics. This has shown the following.

I have also thought about the reasons for taking routine CBCT images that proponents of this technology suggest. There is an absence of evidence for many of the supposed benefits. I certainly would not be exposing my patients to the additional radiation for the following:

  • The need to measure the depth of the alveolar bone.
  • To assess the 3D position of the teeth when deciding upon extractions.
  • The 3D image providing information that we need to plan treatment
  • The need to accurately check the position of the roots after treatment.
  • The need to measure the airway and anatomy of the maxillary complex.

Currently, the evidence suggests that we should use CBCT as a secondary view for complex problems and the management of impacted teeth,

I will conclude with the BOS recommendation on using CBCT. This is clear and is similar to other organisations.

“There is little evidence to support routine CBCT use for orthodontic patients”

Final thoughts?

I know that I have posted about this subject several times and I must be sounding like a stuck record (for those who remember records). However, I cannot help thinking that these studies highlight the risks of CBCT imaging. Unfortunately, we will only know whether CBCT has harmed our patients after a gap of several years.

It would be terrible if a person had cancer because an orthodontist wanted to check on root paralleling or one of the many irrelevant claims that they are currently making. We need to consider whether this superficial information or the fees for the pretty pictures are worth any risk. As usual, lets have a debate in the comments below.

Have your say!

  1. How often do 3D images alter a treatment plan over 2D imaging for an ” average ” orthodontic case?

  2. a properly colimated panorex and cephalometric x-ray have served me well for over 40 years!

  3. Kevin:
    BOSOR states “it’s reasonable to say that the CBCT bone marrow doses might be roughly in the range of 1-4% of those for CT”. Presumably, the risk of developing a malignancy following CBCT would follow the same or similar proportionality? There are no risk free activities in life, whether it be an x-ray or a plane flight. Unlike traditional orthodontics, there is a need to assess the airway but the “airway” is a heterogenous structure, and CBCT imaging of the nasal airway and sinuses is, at least in my experience, crucial for proper diagnosis to establish the site(s) and severity of obstruction in conditions ranging from UARS to mild-moderate-severe OSA.

    • Thanks, but we need to remember that there is no “safe dose”. Furthermore, as far as I am aware there has been research that has suggested CBCT imaging is not sufficiently accurate for the airway. Perhaps, I am wrong but if you have better information from research can you let me have it and I can discuss it in another blog post.

      • Kevin:
        Using your logic of ‘no safe dose’, then no exposure to ionizing radiation follows. Let’s stick to ALARA unless you have new evidence?
        On the other hand, I agree with you that further work needs to be done on upper airway imaging. For example, please see;
        Singh GD. Does head and neck posture affect cone-beam computed tomography assessment of the upper airway? J Oral Maxillofac Surg. 81(7): 804, 2023.

        • I would stick to ALARA but my main point about this is that we should be able to gain clinically important information from a good examination of the patient and their symptoms.

  4. As a Gp doing mostly orthodontics, I’ve used CBCT
    only a few times all related to impacted cuspids and root damaged usually laterals.
    However, in CE for Gp it is pushed heavily for implants and root canals. Wondering if those specialists feel any concern??

    • I’m not sure. Although I am seeing people suggesting that this shoudl be case

    • I would think that Implants and Root Canals are largely treatments that are self selecting to be in older patients and this paper is about radiation exposure in young adults and kids – so I don’t think it would be directly applicable.

  5. “It would be terrible if a person had cancer because an orthodontist wanted to check on root paralleling or one of the many irrelevant claims that they are currently making.”

    Just highlighting this statement. Quite the leap, eh? 🙁

    • Yes, this maybe a leap. But I cannot justify exposing a child to radiation to take a CBCT to check root paralleling. The risk far outweighs any possible benefits. In the UK it is not good practice to take an x-ray for root paralleling as good operators can reassure themselves about this by looking at the crowns of the teeth.

  6. Hi Kevin, I don’t have a strong opinion here, but trying to get a deeper understanding of the issue… Using the same bar for evidence, would a reasonable clinician be able to justify the dose received for a pan/ceph? Thanks!

    • Yes, they would if this was done with a skilled examination of the patient. I can think of little information needed that would involve taking more than 2D views.

  7. Well done Kevin,
    I note the situations in which you would NOT use CBCT.
    I think I might use CBCT In some impacted canine cases to assist in the extraction choice i.e. the lateral first premolar or canine.

    • Yes, I would use a CBCT in impacted canines if I was not certain about the information that I obtained from 2D imaging. It is nice to hear from you.

  8. There are several aligner providers and their KOL, advocating planning aligner treatment in conjunction to a low dose CBCT, with a view of ensuring teeth are not expanded out of the buccal plate. Unsure if the expansion negates the need for extractions but, wonder with the latest research whether this can be justified. How was ortho planned and executed before the dawn ofCBCT’s. We’re many cases expanded out of bone and the consequences thereof. Would be interested in your thoughts Kevin. Best wishes

    • Thanks and this is a good point. However, you are correct as we did manage without CBCTs before they were invented. I still feel that you can get nearly all of the information that we need to plan treatment by doing a thorough and skilled examination of the patient. Perhaps, this is becoming a lost art?

  9. Excellent post as always Kevin, you are quite right to challenge the need for CT scanning for orthodontic patients and I agree that in the vast majority of cases, these images, however incredible they look, cannot be justified.
    I have watched with dismay as lecturers from around the world have illustrated their presentations of the treatment of relatively simple malocclusions, with reconstructed CBCT images.
    If in doubt I would apply the “daughter test” and ask yourself whether you would press the button if it was your own child in the CT machine? I wouldn’t want to risk it.

    • Thanks and yes I would agree with you. I have also seen the “show”involving CBCT images and I cannot help wondering if this is also part of the marketing used by some orthodontists who tell their patients that they have special scans that other practices do not have access to?

  10. The predominant value of a low dose CBCT, in my opinion, relates to evaluating the periodontal – alveolar bone – availability, especially in the crowded dentition. A major reason for tooth crowding relates to ‘bigger teeth’ in ‘smaller, thinner, alveolar bone’
    The issue of additing biology (anatomty/morphology) of the periodontium can only be assessed in a 3d evaluation, ideally a limited field of view, low dose CBCT, which I believe has the same amount of radiation potential as a typical panoramic radiograph, or an FMX. I am still seeking a reference for this statement.
    This analysis will then bring us to the need for incorporating hard and soft tissue augmentation and corticotomies (SFOT) as a viable need for treating the crowded orthodontic dentition for long term success, especially mitigating recession and relapse.
    Much literature is available relative to these two latter issues.
    I am happy to provide additional information upon request
    Colin RIchman DMD
    Periodontics (Focussed on SFOT).

  11. Hello, is it possible to put an implant without having a 3D scan by cbct?

    • I don’t really know as this is not my field. Perhaps someone who does implants can answer this question for us?

    • An implant can be placed without the use of CBCT.
      An excellent clinical evaluation, including bone sounding, can provide much clinically relevant information.
      Just because it can does not mean it should.
      It is not the standard of care.
      Applying the “daughter test” and the “me test,” I would never place an implant without having a volumetric image of the planned implant site.

      Richard Rapoport
      Diplomate Amererican Board of Oral Implantology

      • Hello again,

        Because I am looking to see if there is a 3D scanning method that is non-invasive, that is, without using x-rays. I wonder, is it possible to do a 3D study with magnetic resonance imaging to place implants or another type of scanner?

  12. “There is little evidence to support routine CBCT use for orthodontic patients”

    This is an easy statement to make – I hope – in so far as I doubt many people would routinely use CBCT for ortho patients – though I certainly have been at a lecture by a guy that does seem to do this and the audience was incredulous.

    There might be more people that would want to use CBCT for routine orthodontics (as opposed to routinely use it). But wouldn’t it be better to have a proactive guideline where you could say XYZ circumstances are an indication for CBCT instead of simply 2D views?

    Stephen Murray
    Swords Orthodontics

    • Thanks and yes I have seen the CBCT on everyone presentations and I fear that this sets the standard for people particularly in the USA. The BOS guidelines are clear on the use of CBCT, but do you think that they need to more prescriptive?

  13. Thank you Dr O’Brien for another great post.
    I would like to hear your opinion regarding a few issues related to radiation exposure.
    I there a need for a Ceph X ray for every ortho case? I honestly feel a in good number of cases, a skilled orthodontist can, and does treatment plan cases without the information gained from the Ceph. The main reason the Ceph is taken is those cases, in my opinion, is because of medico-legal purposes.
    The same can be said for taking post-treatment Pan and Ceph. How many cases have been retreated because of findings in a post treatment X ray?
    In my practice, in general, I try to take PA’s of the upper anteriors about 9-12 months into treatment, to check for root resorption, as some studies have found resorption can be spotted around that time, and a Pan a few months prior to the end of treatment to check for any adjustments/corrections that are needed. No post treatment X rays. This just makes sense to me but I don’t have much science to back it up.
    Also, many orthodontists take a Pan about 6 months after initial bonding to check for the need to reposition brackets. How does do we rationalize that with the ALARA principle?
    Thank you

    • Thanks for the comments. When I was clinically active, I followed the BOS guidelines as they are very sensible. In these guidelines they suggest that there is not a need for a ceph in every case. These are only indicated for skeletal problems and if I wanted to obtain additional information on incisal angulation that I could not determine from the clinical examination. I agree with you that a good clinical exam in essential and reduces the need to take radiographs.

      The guidelines suggest that there is no need to take post treatment ceph and pan. If the appliances are not in place what can we do with the information from the radiographs.

      The in treatment pan for root positioning is something that has always been a mystery to me and I think that this is practice in the USA. I and others feel that if the clinical appearance suggests that the roots are parallel there is no need to take radiographs. Again this decision is down to clinical experience and assessment. Thanks for the comments

  14. Why? For posterity – let’s apply the same bar for evidence in this argument to what many do today: Is there convincing evidence that 2D images provide clinical benefits commensurate with the dose, (even if done with a proper examination)? Just because many do it, does this make it right? Thanks in advance…

    • Thanks, and I am not quite sure what you mean. There are some research projects that show decisions do not change with CBCT imaging. There are also many that show the addition of a ceph after clinical examination does not change decisions. I think that this takes us back to carrying out a good clinical examination, then taking views that will give information at the lowest possible dose. At present this is still 2D imaging. There is certainly no indication for “routine” CBCT imaging and this is supported by most guidelines. I hope that I have explained this OK?

      • Thanks Kevin – I don’t want to beat this to death, but I’m asking if there is evidence supporting even 2D imaging given the radiation involved. It sounds crazy, but if a patient asked you to defend taking a progress pan, is there Cochrane-style evidence to point to? Agree with you on the value of the final ceph – have heard this discussed as well.

        • Thanks the only evidence that we can work to is the guidelines produced by the dental associations and radiologists. These are very clear and vary from country to country.

  15. You can now do ultra low dose with CBCT which less than 200 μSv. Why no mention of that in the article?

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