[Development of a respiratory monitoring device for truncal stereotactic radiotherapy using an abdominal pressure-detecting system with Stereotactic Body Frame].

The Stereotactic Body Frame, which was devised as a fastening unit for the irradiation of various truncal lesions, has obtained a good reputation for its high-precision reproductivity. This device is accessorized with 'Diaphragm Control', which can reduce the respiratory movement of intra-thoracic organs. In this study, to investigate the possibility of a respiratory monitor using our device, we try to clarify the relationship between the pressure against the abdominal board of 'Diaphragm Control' and each constrained tidal respiratory movement. Our original software was programmed to detect and analyze these data with our personal computer from some ready-made highly sensitive pressure detectors. In any fundamental performance of this system, response time is less than 1 msec at 115,200 bps, minimum detectable weight is 420 g, linearity correlation between loading weight and pressure index value is seen from 1000 g to 6000 g loading, and reproducibility of measurement is evaluated by coefficient of variation (CV=0.95% at 3000 g loading). It has sufficient capability to be used as a respiratory monitoring device during radiation therapy. In an experiment with three volunteers, the results revealed a positive correlation between pressure index value and ventilation air volume by spirometer. The decision coefficients (R(2)) were 0.7717, 0.7995, and, 0.8684, respectively. Our original respiratory monitoring device can be used for quantitative respiratory suppression and unexpected breathing detection without loading additional stress on the patient.

[Technical considerations on the usage of a general-purpose flatbed image scanner when making a dose-density table].

The DD-System is a dose-distribution system for analyzing the film method with a general-purpose flatbed image scanner. By analyzing the analogue digital conversion(ADC)value of each pixel acquired by the DD-system, we examined the technical problems of measurement with the scanner when making a dose-density table. When film of uniform density was measured, the ADC values distributed normally. Deviation of the values at the same pixel point on another time was about one-ten thousandth of the average. Deviation of the values from the time the scanner was turned on was in the same range. Although it may be negligible, the values measured at a peripheral area on the flatbed deviated about 2SD from the average measured at the central area. Further, deviation of the value obtained with a shade covering the outside of the irradiation field from that taken without the shade was about one thousandth. These deviations are not negligible. In the case of making a dose-density table with a DD-System and a general-purpose flatbed image scanner, the film should be set in the center of the flatbed, and the sampling area should be selected from those areas where the ADC values are distributed normally. Then proper data can be obtained and more accurate tables can be made.