Abstract
Objectives： A limited cone-beam X-ray CT (3DX multi-image micro CT；3DX-FPD) is widely used in dentistry because it provides a lower cost, smaller size, and higher spatial resolution than a CT for medicine. Our recent research suggested that the patient dose of 3DX-FPD was less than 7/10 of that of CT, and it was several to 10 times more than that of dental or panoramic radiography.
The purpose of this study was to evaluate the spatial dose distribution from 3DX-FPD and to estimate the influence of dose by positioning of the region of interest.
Methods： Dosimetry of the organs and the tissues was performed using an anthropomorphic Alderson Rando phantom and X-ray films for measurement of radiotherapeutic dose. Measurements of dose distribution were performed using a cylinder-type tank of water made of acrylic resin imitating the head and X-ray films.
Results： The results are summarized as follows：
1. The dose was higher as the ratio of the air region included in the region of interest increased.
2. The dose distribution was not homogeneous and the dose was highest in the skin region.
3. The dose was higher for several seconds after the beginning of exposure.
Conclusions： It was concluded that patient positioning, as well as exposure conditions including the size of the exposure field and tube current, could greatly influence the patient dose in 3DX-FPD. In addition, it is necessary to consider the influence of image quality for the treatment of dental implants.
