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Oasis Podcasts Oral Radiology

What radiation dose does CBCT impart?

DM PicturePodcast Icon SmallThis series of posts is based on Dr. John O’Keefe’s conversation with  Dr. David MacDonald about cone beam computed tomography (CBCT)

 

 

 

 

 

 

 

Listen to the Audio Interview

 

Interview Highlights

  • First, we need to determine what we mean by radiation dose. We are referring to effective dose which represents the risk of ionizing radiation causing cancer and other genetic damage in those tissues and organs irradiated. 
  • Effective dose is tissue-weighted for the X-ray dose deposited in specified tissues and organs of the body. Important structures such as the salivary glands now have their own tissue weighting.
  • There is no known safe radiation dose; therefore, we need to continue to observe the principle of “as low as reasonably achievable” (ALARA) especially for our most vulnerable patients: children.
  • A recent Australian report in the British Medical Journal, published a follow-up on medical CT on individuals in their childhood is relevant to CBCT use. CBCT imparts a significantly greater radiation dose to the patient’s head than conventional radiography and it is more than just one or two panoramic radiographs, more like at least 10. The increased incidence of cancer after CT scan exposure in this cohort was 24%.
  • Because the cancer excess was still continuing at the end of follow-up, the eventual lifetime risk from CT scans cannot yet be determined.  

Related Posts

 Dr. David MacDonald

After winning his dental fellowship in Glasgow, In London Dr. MacDonald acquired his MSc in Oral Pathology, his Diploma in Dental Radiology of the Royal College of Radiologists and his law degree. His first specialist appointment was as Head of Radiology in Hong Kong, then Edinburgh, then Bergen and finally UBC in late 2003. His research interests are the radiology of the most frequent & important lesions affecting jaws and the application of systematic review to radiology. In 2008 he successfully defended his doctoral dissertation in Edinburgh and passed his fellowship examination of the Royal College of Dentists of Canada. His Wiley-Blackwell textbook was published in 2011; it has so far received 3 outstanding reviews. This evidence-based textbook also uniquely covered the advanced radiology not only of the face & jaws, but also the neck and the base of the skull. The dentist’s understanding of the last areas is essential in our now cone-beam CT-dominated climate.

5 Comments

  1. Tomasz Pater May 21, 2014

    This increased risk of head and neck cancer borders on the unacceptable. CBCT risks should be explained and documented in the patient chart prior to sending the patient for screening. Cases for screening require prudent reasons for diagnostics. Tom

    Reply
    1. David MacDonald May 27, 2014

      Dear Tom,
      I agree! Although technological developments have and will reduce the radiation dose for each exposure, the overwhelming increased availability and wider use of CBCT has and will negate these reductions. Clear clinical indications, ideally evidenced-based, for the prescription for a CBCT and proper informed consent, which includes the potential risks (particularly to children and young adults), are essential to the proper and safer use of CBCT in dentistry. Your suggestion of an appropriate entry in the patient’s chart re the need for a radiographic (including CBCT) referral and just as importantly, the report of the image (including the CBCT database) is already a requirement expressed or implied by law in many jurisdictions across Canada. Many Canadian dental regulatory bodies already mandate these activities.
      Furthermore, certainly in BC, medical radiological facilities will soon be required to enter into the patient’s record the radiation dose received by each patient for each radiological investigation. This information will be collected centrally by the provincial government. The advantage to the clinicians and patients will be that the collective radiation dose to each patient can be inspected and the risk of that patient developing radiation-induced disease determined.
      Dentistry with its preoccupation with low-dose conventional radiography has hitherto largely avoided the intense interest of radiation regulators. This is now about to change with dentistry’s wide-spread use of CBCT.
      Kind regards,
      David

  2. John May 29, 2014

    CBCT is being used for marketing purposes by some specialists. I know first hand some endodontists in Vancouver do a scan on almost every patient that walks in. Most of these scans have no diagnostic value compared to a PA. They’re taken to recoup the cost of the machine and to add it to the reports making them look fancy. Mail outs are sent to dentists with cool CBCT images to advertise the office suggesting they provide better care. Dentists are being told CBCT is standard of care in Endodontics. It’s not; PA is the standard of care and CBCT should only be used for specific cases when benefits outweigh the risks. Since there is no regulation, market pressures rather than evidence will make CBCT standard of care! The sad thing is that patients think they’re getting better treatment. There is no mention of added radiation. They’re being told it’s a cool new machine that takes 3D images!!! Worst kind of false advertising. Dentists who rely on specialists to learn are getting false information and patients pay a price both in $ and health.

    Reply
  3. Dr. Brian Kucey June 2, 2014

    John:
    This brief opinion piece does little to address the topic of the article. There is a wide range of CBCT machines out there and an even wider lack of understanding. To state that “there is no value of a micro CBCT for an endodontic suspected concern is ridiculous”. The smaller FOVs and newer machines have reduced the radiation dosage to that of a digital PA, never mind the conventional film radiograph.

    Reply
    1. JCDA Oasis June 6, 2014

      This reply is posted on behalf of Dr. David MacDonald, author of the present post:

      1. As the writer stated “There is a wide range of CBCT machines out there and an even wider lack of understanding.” The 5 Oasis topics on CBCT are intended to be brief and to serve as pointers, particularly to those who may be thinking about acquiring a CBCT or referring their patients to a CBCT image provider. It is also expected that these topics would provoke a discussion to address such areas of where there is a lack of understanding.

      2. I never said that or intended the message this writer picked-up to be implied. I fully endorse the use for the assessment of endodontic cases, where these are indicated. Indeed in the UBC Endodontics Specialty Program CBCT is required in about a third of all cases referred to it. Such a high level of prescription is indicated because most cases are referred for re-treatment of failed endodontic cases or cases which are too difficult or complex to undertake elsewhere. On the other hand an endodontist colleague told me that in his/her specialty practice very few cases required CBCT.

      3. The writer is not correct with regards to a CBCT unit imparting a similar radiation dose of a digital periapical. This statement emphasizes the “even wider lack of understanding” that exists with regards to this modality. The author is aware of the extent of this misunderstand and I thank him/her for raising this point. Although CBCT units made today impart a lower radiation dose for a comparable investigation than formerly, it is not yet that low. There is no doubt in my mind that the manufacturers will continue to develop units with better and better dose reduction, spatial resolution (image detail) and software. Nevertheless, like the already lower dose conventional imaging, clear clinical indications for the making of ANY exposure is still required. The responsibility for the justification of ANY exposure rests wholly upon the clinician who has prescribed it. Since the advent of CBCT over a decade ago, CBCT use has penetrated almost every aspect of dental practice. Nevertheless, the reader should understand that there is a world of difference between using CBCT to assist the clinician to formulate the treatment plan and using it primarily to sell the treatment plan to the patient or parent. The first is acceptable use if it follows established guidelines (already available for implantology and endodontics), but the latter is not.

      4. My final comment to clarify another possible misunderstanding. Conventional imaging is still superior with regards to spatial resolution and radiation dose (and cost, availability etc.). Conventional imaging remains the supreme imaging system in dental practice. CBCT should be used when cross-sectional imaging is essential for proper management of that particular patient’s problem.

      Although we cannot do much about the” wide range of CBCT machines out there” but by engaging in a discussion we can begin to do something about the “even wider lack of understanding.”

      My heartfelt thanks to the author for beginning this discussion.

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