[Difference of orbit by rotation direction at automatic contouring SPECT using electrostatic capacitance sensor: effect of updating the software].

Automatic contouring system using electrostatic capacitance sensor can sense electrostatic capacitance between a detector and patients' side space. So the system can be set it at an arbitrary distance. On the other hand, this system is so complicated that it is difficult to forecast the detector motion. We studied the difference of the distance according to the rotation direction and verified the system accuracy. In addition, we studied it again after software updating. We compared the set distance with the distance between phantom and detector surface at the closest point. Next, we scanned the phantom with relative 90 degree detector position in a clockwise direction (CW) and a counterclockwise direction (CCW). We took a video of the detector trajectories and compared them. Finally, we compared the results before and after updating the software. At the set distance of 10 mm, the distance between phantom and detector surface distance was 12.00 mm. And at the set distance of 50 mm, it was 52.00 mm. Thus we confirmed the accuracy and repeatability of this system. For the rotation orbit, the CCW rotation kept the distance near the set distance. But the CW rotation rotated over a bigger distance than the set distance at the center position over the phantom. After software updating, this difference became small. Using this system, the rotation orbits differed by their rotation direction. However, after updating software, results indicated that selecting an adequate set distance for every patient and examination makes the image optimum.