日本放射線技術学会雑誌

The effect of the aperture angle of a fluorescence meter on the scatter-to-primary ratio (SPR) was examined. The Monte Carlo program was developed and implemented to simulate an x-ray photon transport. We simulated a situation with divergent beam and x-ray spectra between 40 kV and 150 kV incident on water stabs. The dependence of SPR on tube potential, scatter thickness, and aperture angle was reported as energy-deposition in the phosphor layer. In addition, the average exit angle of scattered photons reaching the phosphor plane was scrutinized. Results indicated that the aperture angle of a fluorescence meter had an effect on SPR. Further, SPR was found to depend on the type of screen phosphor, whereas aperture angle made less difference.

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We studied the evaluation of patient set-up error by verification image using electronic portal imaging devices (EPID). We analyzed which cleared 3 mm in our hospital for visual by using a distance measurement function. The body parts examined included the head and neck, thorax, pelvis and abdomen. The items that were evaluated included shell, Pb block, multi-leaf collimator and landmark. Patient set-up error was 10.4%, with that for the pelvis especially poor. The visual false rate was 17.9%. The result for the abdomen was poor because of the absence of landmark. We showed a decrease in patient set-up error by using EPID and improvement of radiotherapy.

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We measured the radioactivity on patient's upper and lower garments, towels, broad sashes for the bust, and electrodes contaminated by sweat due to exercise ^<201>Tl myocardial perfusion scintigraphy. In measuring activity, a scintillation survey meter adjusted to the energy of ^<201>Tl was used. In measuring the radioactivity of clothing, more than 4 Bq/cm^2 was considered to be a significant level of contamination. We detected contamination in 30% of upper garments and towels, 19% of broad sashes, 8% of lower garments and 4% of electrodes. Among these materials, several items of clothing and other items showed contamination exceeding 40 Bq/cm^2. Towels were remarkably contaminated, with one towel showing a maximum contamination level of 420 Bq/cm^2. Examinations done by exercise ^<201>Tl myocardial perfusion scintigraphy often result in the contamination of clothing and other items through sweating. This contamination is especially common in summer, particularly in upper garments and towels. The contamination ratio for towels was over 50%. The contamination ratio increased as the level of exercise became more difficult. When the exercise load was more than 100W, the contamination ratio was 50%. In cases of extreme contamination, images of contaminated upper garments could be obtained by the scintigraphy camera. The areas of high activity on the images seemed to correspond to areas of the body where sweating was profuse. Based on these results, we should pay close attention to the handling of clothing and other items used in exercise testing by ^<201>Tl myocardial perfusion scintigraphy and the points used in measuring contaminated clothing and other items after testing.

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Prior to coronary angioplasty, the size of the device to be used needs to be measured by quantitative coronary artery analysis. We published the first report on the benefits of the IVR-shot calibration method using a triple rotational axis arm with an on-line system, compared with the calibration method of using catheter size, in a vessel phantom and 11 clinical cases. In this report, by using the same IVR-shot method with an off-line system, we found that the result was closer to the actual value. From the measurement of clinical cases, we obtained a 0.3±0.2mm error by both the catheter method and IVR-shot method. To examine precision, we measured the size of a 40 mm lead ball image by both the catheter method and IVR-shot method. The error of the catheter method was 1.1±0.5mm, while that of IVR-shot was 0.5±0.3mm, indicating that IVR-shot was significantly more precise (p<0.01). More precise results were obtained by off-line calibration with a triple rotational axis.

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