Japanese Journal of Medical Physics (Igakubutsuri)
Online ISSN : 2186-9634
Print ISSN : 1345-5354
ISSN-L : 1345-5354
Volume 27, Issue 4
Displaying 1-3 of 3 articles from this issue
  • Kanae NISHIZAWA, Shin-ichiro MORI, Mari OHNO, Keiichi AKAHANE, Susumu ...
    2008 Volume 27 Issue 4 Pages 153-162
    Published: March 31, 2008
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    Many multi detector-row CT scanners a re used clinically in Japan. Care must be taken because of the higher exposure of MDCT than single-slice CT due to the narrow slice separation of the former.
    Various organ or tissue doses in the abdomen examination for an adult and abdomen-pelvis examination for a child were measured using anthropometric phantoms and TLDs, and their effective doses were evaluated according to ICRP60. For the adult abdomen scan, doses of organs located in the abdomen were around 20-30 mGy. The effective doses ranged from 7-13 mSv and averaged 8.4 mSv. The difference of effective doses between MDCT and single-slice CT was not substantial. For the child abdomen-pelvis scan, organ doses for organs located in the abdomen were around 10-20 mGy. The effective doses were 5-14 mSv. The child abdomen-pelvis scan doses varied greatly between facilities and devices.
    It is necessary to search for the optim a l dose in relation to the image quality when using MDCT.
    Download PDF (1899K)
  • Eiichi SATO, Haruo OBARA, Toshiyuki ENOMOTO, Etsuro TANAKA, Hidezo MOR ...
    2008 Volume 27 Issue 4 Pages 163-171
    Published: March 31, 2008
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    In this paper, we describe a recentlyd e v elopedt able-top plasma x-ray generator utilizing a brass-target triode, which we used in preliminary experiments for the superposition of K-series characteristic x-rays in weakly ionized plasma and for producing their higher harmonics. In the plasma flash x-ray generator, a 200 nF condenser was charged, and flash x-rays were produced by discharging. The x-ray tube was a demountable triode with a brass target containing 65% copper and 35% zinc by weight, and a turbomolecular pump evacuated air from the tube with a pressure of 1 mPa. Target evaporation led to the formation of weakly ionized linear plasma, consisting of metal ions and electrons, around the rod target, and intense characteristic x-rays were produced. At a charging voltage of 50 kV, the maximum tube voltage was almost equal to the charging voltage of the main condenser, and the peak current was 15 kA. When the charging voltage was increased, the linear plasma formed, and the K-series characteristic x-ray intensities of zinc Ka, copper K,8, and copper K/3 lines increased substantially. On the other hand, hardly any zinc KP lines were detected. In particular, we confirmed the irradiation of the second unsharp harmonics of the fundamental Ka lines of copper and zinc. The x-ray pulse widths were 700 ns, and the time-integrated x-ray intensity was 1.2 mGy at 1.0 m per pulse with a charging voltage of 50 kV.
    Download PDF (2299K)
  • Tetsunori SHIMONO, Kichiro KOSHIDA, Hidekazu NAMBU, Yuzo KIKUCHI
    2008 Volume 27 Issue 4 Pages 173-182
    Published: March 31, 2008
    Released on J-STAGE: September 24, 2012
    JOURNAL FREE ACCESS
    There are a number of questions rega r d ing reliability of stereotactic radiosurgery (SRS), stereotactic radiotherapy (SRT), and small-field dosimetry with radiation detectors used for clinical practice due to the lack of lateral electron equilibrium and uncertainty in beam energy. This paper presents a numerical investigation on the effective point of measurement of thimble ionization chambers in megavoltage photon beams with small fields. A dosimetry study was performed for a Microtron that generated 4 MV,6 MV,10 MV, and 14 MV photon beams. To verify the effective point of measurement, measurements were done with detectors commonly used in SRS, such as small-volume ionization chambers with the chamber axis parallel to the beam axis. The effective point of measurement for relative photon beam dosimetry depends on the details of the chamber design, including the cavity length and cavity radius. Moreover, the effective point of measurement also depends on the beam quality and field size. Once the effective point of measurement with the chamber axis parallel to the beam axis is selected appropriately, measured depth-ionization curves can be equated to measured percent depth dose curves for all depths within ±0.5%.
    Download PDF (1702K)
feedback
Top