Cone-Beam CT Dosimetry: Making Sense of it All

By Aaron Molen

There continues to be controversy inside and outside our profession on how much radiation exposure is justified in the pursuit of diagnostic information.  In the end there is no golden answer that will address every situation and ultimately I cannot tell you what’s appropriate in your office.  However, I can arm you with information that will enable you to make an educated decision regarding what’s best for your patients.

Effective Doses
There are many publications and websites that try to accurately compare effective radiation doses, but it’s not that simple.  For example, there are two ways to quantify effective radiation, the ICRP 1990 recommendations and the ICRP 2007 recommendations.  The 2007 recommendations give more weight to the salivary glands, skin, and other organs than before which results in effective doses being higher when measured using the 2007 recommendations. Most publications, though, use the 1990 recommendations which were written before the release of the 2007 recommendations.  Comparing 1990 to 2007 based doses is like comparing apples to oranges so you should double-check which method is being used.

Secondly, the absorbed dose of a CBCT system varies widely within the system itself based on the FOV, scan time, kVp, and mA settings used in the scan.  Recognizing this is important because sometimes CBCT manufacturers will report their scans with the lowest radiation dose and the scans of their competition with the largest radiation doses.  It’s paramount when comparing effective doses between different systems to standardize the previously mentioned settings as much as possible to create a fair comparison.

Finally, the radiation dose measurement depends on the phantom used by the company, or researcher, to measure the dose.  There are a number of different phantoms available that can have a varied number of sensors placed in them to measure the dose.

It’s for the above reasons that I will not be discussing specific radiation doses in this blog post since I believe with all these variables it can be like comparing apples to oranges.  Instead when the time comes to make your decision as to which machine to buy or use I would encourage you to use the information we’ve thus far discussed to filter through the always changing information available in peer-reviewed journals or in the published material from the manufacturers themselves.

Using Cone-Beam in Your Office
Each orthodontic practice has its own unique set of patients and each doctor uses their own personalized treatment approaches to delivering the best care possible to their patients.  Since each practice is unique, each practice will also use cone-beam differently.

In keeping with the ALARA principle I believe orthodontists should answer the following questions before taking a CBCT scan: (1) How does the dosage of this specific scan compare to my normal 2D radiographic series; (2) Does the additional 3D information have the potential to change my treatment plan; and (3) Does the additional 3D information have the potential to create a better treatment outcome for my patient?  How you answer these questions will determine for each patient whether taking a CBCT scan is warranted in their unique case.  Since each office has their own unique set of patients and uses their own unique treatment modalities, some orthodontic offices will take less scans than others.  In the end the goals of protecting our patients, while delivering the best treatment outcomes possible must be balanced by each orthodontist.  Hopefully with the information I’ve provided orthodontists can find that balance with more confidence.

5 thoughts on “Cone-Beam CT Dosimetry: Making Sense of it All

  1. These are the absolute wrong questions we should be asking ourselves. Obviously, it’s impossible to know, in ADVANCE, which patient will benefit from a CDCT scan as none of has X-ray vision. CBCT is an awesome technology. It enables clinicians to VIEW patients in high resolution, undistorted, true-to-size, 3-D. With such a powerful tool, you can’t avoid being a better diagnostician and clinician. AND, since 3-D images are so much easier to interpret, you have an easier time educating parents/patients, thereby coming closer to true informed consent. The question should be, “Why isn’t CBCT the gold standard of care?” We are way too hard on ourselves. Our medical brethren obtain CT scans, which are 1,000 times more radiation, without any regard to ALARA.

  2. At UCSF we have found that a 2D pano is inadequate in many patients, and you often cannot make a determination of the best choice between 3D or 2D with just a clinical examination. By adjusting Field of View and Ma, our radiologic image set is well under 100 microsieverts, while pano/hf/FMXR are well over that. So…for most adults we choose a 3D pano using the CBCT (~50 microsievers) and a 2D ceph (6 microsieverts). For mixed dentition, we are more selective, since they are more sensitive to radiation absorption.
    Jerry Nelson, Acting Chair, UCSF Orthdontics.

  3. I think the 1st question is a good one. the 2nd and 3rd questions are almost the same! Actually, I believe that NOT taking any x-ray will seldom change the treatment plan or effect the treatment outcome. A better question, which should be added is:
    “Is it possible that available 2D images will not reveal what a 3D image usually reveals?”. I have seen cases where nothing abnormal is detected in a 2D image while these abnormal things are detected in a 3D scan.

  4. Thanks for both of these great comments. As an advocate and user of CBCT I actually agree with your points. The idea behind the ‘questions’ is simply to give each practitioner a framework in which to evaluate each patient. We are legally and ethically bound to evaluate each case before prescribing diagnostic records. In some offices, given the practice’s unique demographics and the doctor’s individual treatment philosophy, more CBCT scans may be taken versus another office, or vice-a-versa. One approach is not better than another since each doctor has received training that helps them determine their individual treatment approach. As with all technologies CBCT can be under-utilized or over-utilized. The objective of the blog article is not to support one viewpoint over another, but to simply educate those seeking to learn more about the technology. The goal of our profession should be to advocate for ‘choice’ and ‘trust’. In other words, the goal should not be to push the profession one direction or another, but instead the goal should be to protect each practitioner’s right to exercise their discretion, based on their training, to determine what is in the best interest of each patient. I hope this clarifies any confusion regarding the intent of the original blog post. (Aaron Molen)

  5. The new CBCT information might provide additional details that were not as obvious using conventional x-ray scans. We’re referring our CBCT scans to Marcilan (www.marcilan.com). They have a team of expert oral and maxillofacial radiologists who can eliminate any pathology or diagnose TMJ and sinuses…etc. Their radiology reports are done within 24 hours usually.

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