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.

Who moved my DICOM?

by Juan Martin Palomo DDS, MSD

Most orthodontists associate the term “DICOM” with Cone Beam Computed Tomography (CBCT).  DICOM however represents much more than that.  DICOM, which stands for “Digital Imaging and Communications in Medicine,” is the international standard for all medical images and related information.  Any radiograph, 2D or 3D, as well as photographs and even text documents can be stored as DICOM files.  DICOM represents is a non-proprietary file format that can be accessed by any software regardless of the hardware and software used in the capture stage.  Think of it as the equivalent to a .jpg, .tif, or .pdf, with many extras. Most importantly, it replaces company-specific file formats making data accessible by anyone in the healthcare field.

Many of us have had to at some point in time change management software systems, or send information to referring or transfer offices.  This would be very simple if everybody involved used the same software or if all software read the same formats. When this is not the case complications may occur.  Software programs use their own proprietary file formats because 1) they have invested a lot of time and resources to make the files efficient, and 2) they want to protect their intellectual property.  This can be a shortcoming to the user if there is no option for exporting the data in a format that can be opened with other programs.  It is important for anybody buying clinical software (regardless if it comes with x-ray equipment or not) to make sure that not only can it read DICOM files, but that it is able to export data into that format too.

A DICOM file has multiple layers of information embedded within it.  A DICOM file contains the patient’s name, demographics, information about the capture system, the date, etc. So a DICOM file located on a computer hard drive is much better than an unlabeled radiograph or picture laying on the desk. It has all the identifying information embedded within it.  This is obvious when a DICOM file is opened and the patient’s personal information is quickly displayed.  Additionally, most DICOM viewers also use the data embedded within the file to assign the patient’s identity, helping avoid the mismanagement of images (i.e. placing the wrong image into a patient’s file).  If your current software does not read DICOM files, don’t worry.  There are plenty of DICOM readers free of charge that can be easily downloaded that will perform most necessary tasks.

Lastly, when archiving images, make sure to do so in the DICOM format because there is no guarantee that your specific software will be available forever.  I would further recommend that you go back to your previously archived files and see if they are in the DICOM format. Don’t be surprised if they are not!  Luckily most, if not all, dental and medical capture devices now provide a “save as DICOM” option. Just be aware that DICOM is not usually the default.