Meetings » 1st CTUG Meeting » Should Diagnostic Reference Levels (DRLs) be adopted for dental CT scans?

Should Diagnostic Reference Levels (DRLs) be adopted for dental CT scans?

R. Anthony Reynolds

Image Diagnostic Technology Ltd, 110 Harley Street, London W1N 1AF


Permanent dental implants offer a stable, comfortable and enduring alternative to removable dentures, but the surgical procedure demands considerable skill and detailed planning. Pre-operative imaging informs the quantitative assessment of jaw bone thickness and density at potential implant sites, and helps the surgeon avoid sensitive structures such as nerves. Reformatted computed tomography (CT) scans have become the imaging modality of choice for pre-implant assessment, because the non-distorted images are suitable for direct measurement, and the bone density can be estimated directly from the CT numbers. Over a thousand CT scans are carried out in the UK annually for pre-surgical planning prior to the placement of dental implants.

For many years the main disadvantage of CT was considered to be a relatively high radiation dose to the patient. One reason for this perception was that the earliest dosimetry studies were based on outdated equipment (by today's standards) whereas significant improvements in CT Scanner design, beam collimation, and detector efficiency have recently taken place. Another reason is that doses from dental CT scanning can vary by a factor of 10 or more from one hospital to another. This is in part because the lower dose limits at which images become clinically unacceptable are not well understood.

Image Diagnostic Technology Ltd (IDT) provides a commercial service to dental implantologists by arranging for patients to be CT scanned at participating hospitals, retrieving the computer data, and generating reformatted images and 3-D views. To manage the variability in patient doses IDT establishes strict scanning protocols to which participating hospitals adhere. To optimise these protocols IDT obtains Effective Doses (EDs) for each scanner model, following methodologies developed by the ImPACT group.

The ED is calculated from measured CT Dose Index (CTDI) values using the CTDOSE software and the NRPB SR250 datasets, with matching of new scanners to the existing datasets done by ImPACT. Results obtained to date show that adequate image quality for surgical planning can be achieved for EDs of 0.1 - 0.3 mSv for a typical maxilla and 0.2 - 0.6 mSv for a typical mandible, for a range of scanner models. These numbers could form the basis for DRLs for dental CT scanning.

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