Time filter

Source Type

Yokohama-shi, Japan

Fujibuchi T.,Kyushu University | Yonai S.,Japan National Institute of Radiological Sciences | Yoshida M.,Nuclear Safety Technology Center | Sakae T.,University of Tsukuba | And 3 more authors.
Health Physics

Photonuclear reactions generate neutrons in the head of the linear accelerator. Therefore, some parts of the linear accelerator can become activated. Such activated materials must be handled as radioactive waste. The authors attempted to investigate the distribution of induced radioactivity using photostimulable phosphor imaging plates. Autoradiographs were produced from some parts of the linear accelerator (the target, upper jaw, multileaf collimator and shielding). The levels of induced radioactivity were confirmed to be non-uniform within each part from the autoradiographs. The method was a simple and highly sensitive approach to evaluating the relative degree of activation of the linear accelerators, so that appropriate materials management procedures can be carried out. © 2014 Health Physics Society. Source

Hirata G.,Yokohama Rousai Hospital
Clinical calcium

Measurement of the bone mineral density have shown that lactating women had 1 to 3% decrease in bone mineral density. Post pregnancy osteoporosis is rare condition that causes fragile fracture mostly in vertebrae. The bone loss in lactating women is caused by calcium loss, decrease in estrogen level, and increase in PTHrP (parathyroid hormone related protein) level. Some data have shown that extended lactation and amenorrhea had an association with the degree of bone loss. Mostly, the bone loss of the lactating women recovers to the baseline level, soon after the weaning, and there is no long term effect. Post pregnancy osteoporosis should be concerned, when we see a lactating woman with fragile fracture of the vertebrae. Source

Fujibuchi T.,Ibaraki Prefectural University of Health Sciences | Fujibuchi T.,University of Tsukuba | Obara S.,Ibaraki Prefectural University of Health Sciences | Yamaguchi I.,Japan National Institute of Public Health | And 4 more authors.
Radiation Protection Dosimetry

The radioactivation of linear accelerator components for radiation therapy is interest for radiation protection in general, and particularly, when decommissioning these structures. The energy spectra of gamma rays emitted from the heads of two accelerator models, EXL-15SP and Clinac iX, after 10-MeV X-ray irradiation, were measured using a high-purity germanium semiconductor survey meter. After spectrum analyses, activities of 24Na, 28Al, 54Mn, 56Mn, 57Ni, 58Co, 60Co, 64Cu, 65Zn, 122Sb, 124Sb, 181W, 187W, 196Au, and 198Au were detected. One centimetre deep dose-equivalent rate of the heads of the linear accelerator was measured using the survey meter. The dose rate decreased to ~10 % of its initial rate after 1 week. Long-term activations were few, the radioactivity level was low, and a cooling time of several days was effective for reducing dose rate to an acceptable level for decommissioning. © The Author 2011. Published by Oxford University Press. All rights reserved. Source

Horitsugi G.,MI Clinic | Fujibuchi T.,Ibaraki Prefectural University of Health Sciences | Yamaguchi I.,Japan National Institute of Public Health | Eto A.,MI Clinic | And 6 more authors.
Radiological Physics and Technology

The cyclotron at our hospital has a self-shield of boron-containing water. The amount of induced radioactivity in the boron-containing water shield of a compact medical cyclotron has not yet been reported. In this study, we measured the photon and neutron dose rates outside the self-shield during cyclotron operation. We estimated the induced radioactivities of the boron-containing water used for the self-shield and then measured them. We estimated the activation of concrete outside the self-shield in the cyclotron laboratory. The thermal neutron flux during cyclotron operation was estimated to be 4.72 × 10 2 cm -2 s -1, and the activation of concrete in a cyclotron laboratory was about three orders of magnitude lower than the clearance level of RS-G-1.7 (IAEA). The activity concentration of the boron-containing water did not exceed the concentration limit for radioactive isotopes in drainage in Japan and the exemption level for Basic Safety Standards. Consequently, the boron-containing water is treatable as non-radioactive waste. Neutrons were effectively shielded by the self-shield during cyclotron operation. © 2012 The Author(s). Source

Fujibuchi T.,Ibaraki Prefectural University of Health Sciences | Horitsugi G.,MI Clinic | Yamguchi I.,Japan National Institute of Public Health | Eto A.,MI Clinic | And 6 more authors.
Radiological Physics and Technology

Some medical compact cyclotrons have selfshielding to reduce neutron fluxes. Thermal neutron fluxes in an 18-MeV unshielded cyclotron room and in a 16.5- MeV self-shielded cyclotron room were evaluated. In addition, the radioactivities in concrete and metals due to thermal neutrons in the cyclotron rooms for 30 years were calculated of operation such that the sum of the ratio of the nuclide concentration to the nuclide clearance level was equal to 1. The thermal neutron flux from the unshielded cyclotron was approximately 10 2 cm-2 s-1, whereas that from the self-shielded cyclotron was approximately 102 cm-2 s-1. The thermal neutron fluxes for concrete, stainless steel, vessel steel, and aluminum that reached their clearance levels were 9.80 × 104, 2.17 × 103, 1.87 × 104, and 2.41 × 10 5 cm-2 s-1, respectively. The specific activities in the cyclotron room were found to be sufficiently below the clearance level when the self-shield was employed. © Japanese Society of Radiological Technology and Japan Society of Medical Physics 2012. Source

Discover hidden collaborations