Anatomically shaped cranial collimation (ACC) for lateral cephalometric radiography: a technical report

Abstract

Lateral cephalograms in orthodontic practice display an area cranial of the base of the skull that is not required for diagnostic evaluation. Attempts have been made to reduce the radiation dose to the patient using collimators combining the shielding of the areas above the base of the skull and below the mandible. These so-called “wedge-shaped” collimators have not become standard equipment in orthodontic offices, possibly because these collimators were not designed for today's combination panoramic–cephalometric imaging systems. It also may be that the anatomical variability of the area below the mandible makes this area unsuitable for standardized collimation. In addition, a wedge-shaped collimator shields the cervical vertebrae; therefore, assessment of skeletal maturation, which is based on the stage of development of the cervical vertebrae, cannot be performed. In this report, we describe our investigations into constructing a collimator to be attached to the cephalostat and shield the cranial area of the skull, while allowing the visualization of diagnostically relevant structures and markedly reducing the size of the irradiated area. The shape of the area shielded by this “anatomically shaped cranial collimator” (ACC) was based on mean measurements of cephalometric landmarks of 100 orthodontic patients. It appeared that this collimator reduced the area of irradiation by almost one-third without interfering with the imaging system or affecting the quality of the image. Further research is needed to validate the clinical efficacy of the collimator.

Validation of anatomically shaped cranial collimation (ACC) in orthodontic lateral cephalography

“…This anatomical variability is of the order of five times greater than the differences found by a different geometry with different X-ray systems. 9 Therefore, it is not expected that hindrance in landmark identification would be significantly different with a different X-ray system.…”

“…9 This design was based on the average anatomy of a group of Dutch orthodontic patients and the geometry of a panoramiccephalometric X-ray unit. It was designed to be mounted on the ear rod of the cephalostat.…”

Dose reduction in orthodontic lateral cephalography: dosimetric evaluation of a novel cephalographic thyroid protector (CTP) and anatomical cranial collimation (ACC)

“…Recently, the anatomical cranial collimator (ACC) was introduced to shield the area cranial of the skull base from radiation. 2 This cranial area is without diagnostic information to the orthodontist. Another area that is in the field of view of lateral cephalograms without diagnostic information is the thyroid region.…”