Recently, the radioactive source Jr-192 has been replacing Co-60 as a high dose rate (HDR)remote afterloading system (RALS) brachytherapy source. Two-dimensional relative dose distributions have been measured around HDR Jr-192 source in a water phantom within a plane through the source axis. Measurement has been made for distances between 1 and 10 cm and for angles 0to 90 degree from the source center. Data have been corrected for background and finite detector volume. Two physical parameters, radial dose function and anisotropy function, have been calculated from measured data. The results indicate that the anisotropy increases as the angle decreases. This effect resulted from increasing of attenuation of the source encapsulation wall at small angles.
Recently, some new ortho screen-film systems (Konica EX system, Fuji AD system and Kodak IEF system) are being developed. The granualities of these systems have been greatly improved and gross fogs are lower than those of traditional ortho screen-film systems. Even if the radiographs with the new ortho screen -film are pr o cessed at higher temperature than with the old ortho system such as Lanex Medium /TMC-RA (Eastman Kodak), the deterioration in the image quality is negligible. Furthermore, the speed of the screen-film systems increases as the developing temperature rises. Therefore, there may be the potential to reduce patients' radiation exposure without greatly decreasing the image quality. At that time, the problem arises how to determine the appropriate developing temperature. The limit of developing temperature for the new ortho system was determined as the temperature for getting the same gross fog in old ortho-system. In this report, phantom radiographs were made at various de veloping temperatures and the comments about the higher limit of the developing temperature were solicited from medical doctors who evaluated them. Consequently, it has been confirmed there are sufficient image qualitiy in the radiographs which were developed at the higher developing temperature than at the temperature used in many faculities now.
Phase-contrast X-ray computed tomography (CT) enabling the observation of biological soft tissues without contrast enhancement has been developed. The X-ray phase shift caused by an object is measured and input to a standard CT reconstruction algorithm. A thousand times increase in the image sensitivity to soft tissues is achieved compared with the conventional CT using absorption contrast. This is because the X-ray phase shift cross section of light elements is about a thousand times larger than the absorption cross section. The phase shift is detected using an X-ray interferometer and computer analyses of interference patterns. Experiments were performed using a synchrotron X-ray source. Excellent image sensitivity is demonstrated in the observation of cancerous rabbit liver. The CT images distinguish cancer lesion from normal liver tissue and, moreover, visualize the pathological condition in the lesion. Although the X-ray energy employed and the present observation area size are not suitable for medical applications as they are, phase-contrast X-ray CT is promising for investigating the internal structure of soft tissue which is almost transparent for X-rays. The high sensitivity also provides the advantage of reducing X-ray doses.
Conceptual design of a proton rotating gantry for cancer therapy has been made taking in mind the installation in the new proton cancer therapy facility. Since beam delivery system affects the gantry design, several methods of forming the uniform irradiation field have been compared and their merit and points to be noticed have been clarified. Based on the review of the technical aspects of the present proton rotating gantry, an isocentric gantry with a single bending plane was proposed to decrease the magnet weight and power and to secure the free space allowing the table carrying the patient couch to rotate around a vertical axis and translate. Although the double scattering system will be installed in the gantry at the early stage, there remains room for installing more efficient and elaborate method like the beam optical method.
Dosimetry of small radiation fields for 6 MV or 18 MV x-rays have been studied with four kinds of ionization chambers (0.6,0.075,0.0094 and 0.006 cm). Special consideration in this study was given to i) the central axis percentage depth dose curves for square fields, ii) the variation of dose with field size and of profile on penumbral region, and iii) the normalized peak scatter factor. It is advisable to use the ionization chambers with small measuring volume for small field. But as its volume decreases, the variation of response due to stem and cable leakage for irradiation increases.
We have developed CAI (computer aided instruction) coursewares for nursing education and have learned advantages of CAI, which are as follows; 1) one can have an indivisual self-teaching,2)one can select the courseware suitable for each understandings. These results indicate that CAI is effective tool for nursing education. Further, in these work we have developed a new courseware, focused on geriatrics nursing. We will report the needs and background of CAI for effective education in geriatrics nursing. We will also report the assesment and outcome of this system based on the results of trial use in the nursing college.
There is considerable evidence that substantial reduction in medical exposures are possible without detriment to patient care. Control of medical exposures should be essential component of quality control (QC) for diagnostic radiology. Although many investigators reported patient doses measured with various methods, standardized method for patient dose measurement is necessary for QC and QA. The present paper reports reviews and discussions on following subjects necessary to make a protocol for a standardized method in Japan; (1) Purpose of patient dose measurements, (2) Surface dose to be measured for monitoring patient doses, (3) Protocols in UK and USA for example, (4) Three kinds of surface dose, (5) Six dose units used in surface dose, (6) Calibration of dosimeters for diagnostic X-rays, (7) Permissible accuracy of measured patient doses. A protocol should be nationally agreed methods for monitoring patient doses in diagnostic radiology, that should be able to easily carried out by radiological technologists.
In ICRP Publication 60 (The Recommendations of the Commission-1990), the Commission has recommended that, once pregnancy has been declared, the equivalent dose limit to the pregnant worker should be 2 mSv for the surface of her abdomen during the remainder of the pregnancy. In addition, the Commission has recommended that the fetus should be afforded the same broad level of protection as required for members of the public. The verifications of whether the Commission's recommendations on the occupational exposure of pregnant women can be ensured under their working conditions are carried out. From the results, it seems to be unsuitable to accept the recommendations. It is proposed that external exposure for pregnant workers estimates ambient dose equivalent, H (10) on the surfaces of their abdomens and the dose limit to the pregnant women should be 1 mSv during the remainder of the pregnancy.
This paper is a review of the present status of medical radioactive waste management. The primary sources of radioactive waste arise from medical utilization involving in in vivo tests, in-- vivo treatments, in vitro tests, and activated materials. Radioactive wastes contaminated by 19clinically applied radioisotopes (RI) are classified as " Medical" by The Japanese Radioisotope Association (JRA). Medical solid and liquid wastes are routinely collected and disposed of by The JRA at their Takizawa Institute. Medical radioactive wastes amount to about 44% of all collected radioactive refuse in Japan with the exception of power plants. The half-lives of these RI are relatively short. Pos i tron emitters, for example, used for PET tests have very short half-lives ranging from about a few minutes to an hour. Materials contaminated by these RI are legally disposed of as radioactive wastes. In contrast, radioactive contamination found in the underware of 131 I in -vivo treated patients is not legally controlled. Activated parts of cyclotrons; target foils, electrodes etc., are also not legally controlled and are voluntarily isolated at each facility.
Several topics related to the radiation protection in medical use of ionizing radiation are discussed. The occurrence of the acute effect of ionizing radiation among the patientes who are exposed in endvascular surgery may show the negligence of medical physicists working in the field of radiation protection. Publication of the "Basic Safety Standards" of Internatiol Atomic Energy Agency will accelerate the movement of changing the regulatory system as to fit with 1990 recommendation of ICRP, which may cause several exhausting problems for medical physicists. Necessity of the discussion on the quantity used in diagnostic exposure is also pointed out.