While patients are irradiated by a proton beam for the cancer therapy, high energy protons unavoidably traverse the air of the treatment room. This makes the air getting radioactive due to nuclear reactions such as the p-alpha reaction in nitrogen nuclei. Thus, the measurement of the radioactive concentration of the air is important from the view point of radiation protection. The response of a gas monitor depends not only on the energy spectrum of emitted beta-rays but also on the wall material as well as the geometry of its ionization chamber. Consequently, it is necessary to calibrate the detector. Since samples having some standard conentration of radioactivity are not available for those nuclei of short half lives, such as carbon-11, nitrogen-13, etc., an EGS-4 simulation code was utilized to evaluate the detector response. The result shows the detector used in this facility (Tritium Room Monitor MGR-120X, Aloka) is about ten times less sensitive to beta-rays of tritium than to those of carbon-11 and nitrogen-13. With this consequence the radioactive air contamination of the treatment room is estimated to be 0.6 Bq/cc at a maximum, where the energy and the fluence rate of the proton beam are 160 MeV and 6.4 x 106cm-2 sec-1, respectively.
We have proposed the scatter correction method which considered energy spectra of scattered photons using four energy windows, i. e., three abutted energy windows (a left, a right, and a middle window) and a reference window. These three windows were located in the photopeak and the reference window was set in the lower energy region than the photopeak. In the method the count of scattered photons within the three abutted windows was estimated by using a regression relation between the following two ratios. One was the ratio of the estimated count of the scattered photons included in the left window to the total count within the reference window. The other was the ratio of the count of the scattered photons within the three abutted windows to the total count within the reference window. In this paper, we showed the optimal width and position of each energy window and improvement of image contrast from the results of phantom experiments.
No modality for selective heating of bone seems to have been reported in journal. Selective heating of bone by 332 kHz ultrasound wave was experimentally verified using bovine bone slice of 10mm thick covered by muscle layer of 10 mm thick and fat layer of 10 mm thick in the degassed water. The temperature rise, after 200 s of irradiation, at the center of the bone was 29.5°C that of muscle and fat was 9.0°C and 15.0°C respectively. The intensity of emitted ultrasound wave was approximately 100 W. Experiments were conducted using living rabbits resulting selective heating of the thighbone. Selective heating of bone may be of future clinical importance for treatment of bone cancer, rheumatism, bone fracture, and/or osteoporosis.