Objectives: To compare the reproducibility of three-dimensional cephalometric landmarks on three-dimensional computed tomography (3D-CT) surface rendering using clinical protocols based on low-dose (35 mA s) spiral CT and cone-beam CT (I-CAT). The absorbed dose levels for radiosensitive organs in the maxillofacial region during exposure in both 3D-CT protocols were also assessed.

Materials and methods: The study population consisted of 10 human dry skulls examined with low-dose CT and cone-beam CT. Two independent observers identified 24 cephalometric anatomic landmarks at 13 sites on the 3D-CT surface renderings using both protocols, with each observer repeating the identification one month later. A total of 1920 imaging measurements were performed. Thermoluminescent dosimeters (TLDs) were placed at six sites around the thyroid gland, the submandibular glands and the eyes in an Alderson phantom to measure the absorbed dose levels.

Results: When comparing low-dose CT and cone-beam CT protocols, the cone-beam CT protocol proved to be significantly more reproducible for 4 of the 13 anatomical sites. There was no significant difference between the protocols for the other 9 of 13 anatomical sites. Both low-dose and cone-beam CT protocols were equivalent in dose reduction for the eyes and submandibular glands. However, thyroid glands were irradiated four times more with low-dose CT.

Conclusions: Cone-beam CT should be preferred over low-dose CT for three-dimensional bony cephalometry.

Conflict of interest: None declared.