患者被曝線量に対する回転パノラマX線撮影時の1次、2次スリットの軸合せ不良が及ぼす影響

抄録

The ICRP Publication in 1982 recommended that “When using panoramic equipment, the alignment of tube (with slit beam-limiting device) and film shield (again with its slit) is critical, and this shall be checked at suitable intervals.” However there was no simple method for estimating the increased radiation dose of a patient from incomplete slit alignment in rotational panoramic radiography.
The purpose of this investigation was to obtain the data on the integral absorbed dose (energy imparted) received by the patient when using rotational panoramic radiography at several different incomplete slit alignments. The integral absorbed doses were calculated by the energy fluence method. The alignment of the first slit and the second slit were checked using dental film and a fine wire. The dental films were placed on the second slit either on the side nearest to the X-ray source or on the side behind the slit, and a fine wire was positioned on the film surface. The densitometric traces were measured by means of a microdensitometer in a direction perpendicular to the slit image. The X-ray intensity distribution of the first slit and second slit was obtained by determining the film density when the film was place in front of and behind the second slit, and applying H-D curves.
The results were as follows:
1) Using rotational panoramic radiography with incomplete slit alignments, the patient exposure dose should be increased from 1. 2 to 2 compared with complete alignment.
2) The increased radiation dose can be estimated by the following expression
In the second slit position, X₁ is an area of X-ray intensity distribution from the first slit and X₂ is a similar value of the second slit when slit alignment is complete, similary X'₁ and X'₂ are the values obtained with an incomplete slit alignment. The value of k is a valiable factor of beam quality dependent on the kVp.