January 21, 2014

Careful with that radiation..Eugene

Careful with that radiation….

I know that I have said this before, but occasionally a paper comes along that really makes me think and this is one.  I came across this in the EJO advanced section of the website.  This study was carried out by a good team based in Leuven and they investigated the diagnostic utility of CBCT radiographs and essentially persuaded me to be careful of that radiation. It also allowed me to part name this blog on a very old Pink Floyd track that reminds me of my teenage years…Careful with that axe..Eugene

I have been using these for several years on a limited number of my patients and I have always been surprised at the quality of the images that are produced.  However, I remember the first time that we used a CBCT for a patient when a colleague of mine showed me a great image of a palatally placed canine resorbing a lateral incisor.  We were all impressed.  We then asked to see the DPT that had been taken as the “first line” radiograph. This showed extensive resorption of the lateral incisor!  We were just more confident in what we had seen.  This is the concept that has been investigated in this paper.

 Orthodontic treatment planning for impacted maxillary canines using conventional records versus 3D CBCT

Ali Alquerban et al

European Journal of Orthodontics Advance access publication 2014

Doi: 10.1093/ejo/cjt100

In this study they attempted to answer a simple question  “to compare orthodontic treatment plans in maxillary canine cases using conventional records and Cone Beam CT”.

They took 40 sets of records of patients who had two dimensional radiographs and CBCTs taken.   They were then viewed, along with study casts, by panel of experience orthodontists.   They recorded diagnostic information, planned the treatment and noted their level of confidence in their treatment decision.

 What did they find?

They found that the use of cone beam CT resulted in significant differences in the accuracy of diagnosis of canine position, canine development and detection of root resorption of lateral incisors.   At this point things look good for CBCT.

However when they evaluated the treatment decisions there were no differences in the planning decisions based on conventional views versus the CBCT dataset. Nevertheless, the level of their confidence in their decisions was higher with CBCT.

 So what does this mean?

They discuss the many implications of their findings in great detail in a lengthy discussion section. I will not go into all of this. However my interpretation is that the new technology helps us visualize problems well.  In other words, it can increase our perception and we feel more confident in our decisions

However, when we consider our judgements we can still produce clinical decisions using less sophisticated methods. This may be because the orthodontists who took part in the study were very experienced and they probably used a combination of their clinical experience from viewing conventional radiographs. I’m not so sure that this would be the case less experienced operators. There is a danger that less experienced orthodontists may prefer to use CBCT views.

This does bring me to considering radiation dose. ALARA and Sedentext EU guidelines state that CBCT should only be used in selected cases in which conventional radiographs cannot provide sufficient information. We should always bear in mind the harmful effects of radiation and remember this dose is accumulative

They also point out that there is a long term risk in radiation induced carcinogenesis and this risk may increase younger patients.


Will this paper influence practice?

I certainly hope so, and I will aim to reduce my use of CBCT to only those patients who I feel would benefit from more diagnostic accuracy.  At present, the risks are still too high when we can use conventional methods with equal effectiveness.


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Have your say!

  1. Just came from a meeting where iCat was present. Their latest generation scanner produces full head scans that expose the patient to less than half the amount of radiation (11µS) of a digital panoramic view… or so they claim.

    • Hi Kevin, thanks, I have discussed this with my radiologist colleague and he is going to get back to me on this one, as he is not sure that this is 100% correct

  2. I just received another comment from Kevin Walde by email, I have pasted this and my reply below.

    Hi Kevin

    I’m a Pink Floyd fan but I’m not familiar with the track you referenced in you latest Blog?


    [email protected]

    Hi Kevin, thanks for the message. I think that I was a little obtuse in the blog. The track was Careful with that Axe, Eugene. It was never released as an album track apart from a live version on Ummagumma. I think that this was released in 1969, which is clearly a long time ago. This was well before they lost their way in the post Wall days. Here is a you tube link to a live performance in Brighton in 1972. It is a classic but hard going! http://www.youtube.com/watch?v=2_KGxo2W9A0

    Comments like this are great, because it takes the blog away from ortho, to other areas that may be interesting (or not)..


  3. Guys, when you’re done setting the controls for the heart of the sun, would you venture an opinion on CBCTs being more often cited by US speakers than European ones, and whether there is any obligation to declare commercial interests here or there?

    I ask this because I have done my core CPD on radiology every so often, and no one seems to be in a rush to promote more CBCTs on these courses, but they do seem to spring up frequently in talks by US ortho speakers.

    But if my OPT machine broke down tomorrow, I would be interested to find out how a modern CBCT set up compares to an old OPT machine in terms of dose.

    • You have made interesting points. While it is easy for people to be cynical and suggest that commercial interests are behind some of the recommendations, there is also a clear possibility that some people genuinely believe that the adoption of new technology is always going to be better than the “old”. In this respect it is worth the increased radiation dosage. There are also plenty of stories about disease being detected by using a CBCT and this was missed by using conventional methods. It appears that the dosage from CBCT machines is being reduced but my radiology colleagues at Manchester say that this is not always the case when the claims are made and you need to check very carefully with the manufacturers to be totally sure.

  4. iCat radiation level comparisons
    I-CAT Volumetric CT Radiation Dosage Comparison
    I-CAT 20 second scan: 68 uSv
    Exposure is in “Pulsed” mode, actual exposure time is about 3.5 seconds for a 20 second scan
    I-CAT 10 second scan: 34 uSv
    Daily background: 8 uSv
    Panoramic (Average): 10-15 uSv
    Digital Panoramic 4.7 – 14.9 uSv
    Highest Film Pan 26 uSv
    Full mouth series: 150 uSv
    Medical CT 1200-3300 uSv*
    The above courtesy of:
    Dr. Sharon Brooks, Dept. of Radiology, University of Michigan
    *Dr. Stuart White, Dept. of Radiology, UCLA

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