Answer to Question #13809 Submitted to "Ask the Experts"

My 14-year-old son had panoramic x ray done at the orthodontic office. He had a lot of radiation in the past and I am concerned. I read the radiation exposure from a panoramic x ray is about 0.02 mSv. The machine used was labeled as a Soredex Cranex and it looks like a cone beam computed tomography (CBCT) machine, which I understand results in a higher radiation dose. Can you please tell me the radiation dose my son received from this study?

I understand your concern over radiation dosages for your son. All extraoral dental radiology units do look very similar and most units are dual units, meaning that they can perform either a basic 2D panoramic image or a 3D cone beam CT volume. I would not be concerned with the appearance of the unit if they only took a panoramic image. It does not mean that a cone beam CT was taken. In addition, the extensive research on panoramic units reveals that it utilizes a very low amount of ionizing radiation.

Identifying dosages on a per-patient bases can be problematic because there are many factors that must be taken into account including the exact location of the patient in the machine, the size of the patient, and the exact region that was ionized. One of the parameters we will use to evaluate dosimetry is known as the "effective dose" which does take into account the average volume and sensitivity of the tissues to ionizing radiation utilizing the latest International Commission on Radiological Protection (ICRP) methods of determining how sensitive certain tissues are to ionizing radiation known as "tissue weights." The most current method for determining tissue weights was conducted in 2007 and used a more conservative method than the one employed at the previous evaluation in 1990. Effective doses are reported in microsieverts (uSv) or millisieverts (mSv). In dentistry the doses are quite low, so you will see uSv used in dental dosimetry research.

Panoramic imaging dosimetry research will reveal a variety of doses based on the panoramic unit employed as well as whether the older tissue weights (1990) or newer tissues weights (2007) were utilized. It also appears that the Soredex company has since been bought by Kavo and those units do not appear to be actively distributed by Kavo, so the dosimetry information is not readily available from the manufacturer. A 2005 article in Dentomaxillofacial Radiology notes that Cranex units produce an average effective dose of approximately 4.5 uSv using the older tissue weights (1990). According to an article in the Journal of the American Dental Association, that dose roughly translates to approximately 14.2 uSv when updated to include the latest and most conservative tissue weights (2007). For comparison, the amount of radiation one receives every day just being alive on the Earth, known as ubiquitous background radiation, equals approximately 8.5 uSv. This means that your son received a dose equivalent of approximately 1.7 days of background radiation.

I hope this helps you to better understand the low amount of radiation that your son received and helps to put your mind at ease.

Heidi Kohltfarber, DDS, MS, PhD