小照射野歯科用CT 装置での患者被曝線量の検討

抄録

A limited cone-beam X-ray CT, known as Ortho-CT, was developed based on multi-functional panoramic apparatus and was improved as a "3DX multi-image micro CT (3DX)" for practical use. Recently, a new type of 3DX (3DX-FPD) having a flat panel detector instead of an image intensifier has been released. 3DX-FPD adopts two kinds of columnar radiation field, 40×40 mm (diameter×height) and 60×60 mm. Some investigations of the limited cone-beam CT apparatus including 3DX demonstrated high spatial resolution, however, different values were measured in a few surveys on dosimetry of 3DX. In addition, there has been no report on the dose of 3DX-FPD. Therefore, this study set out to estimate the dose difference among 3DX-FPD and other conventional radiographies (dental radiography, panoramic radiography and computed radiography (CT) and between two radiation fields in 3DX-FPD. Dosimetry of the organs and the tissues was performed using an anthropomorphic Alderson Rando phantom and a thermoluminescence dosimeter.
The results are summarized as follows:
1. The dose of 3DX-FPD was less than 7/10 of that of CT, however, it was more than 10 times that of dental radiography or several times that of panoramic radiography, respectively.
2. The absorbed dose in a field of 60×60 mm for the contralateral mandibular molar, eye, parotid gland and skin regions was almost 2 times higher than that in 40×40 mm with 3DX-FPD.