Numerical data of several quantities related bremsstrahlung were required in the development of a Monte Carlo code simulating electron-photon showers. The cross section formula used here are those recommended by Koch and Motz as giving the best representation of theoretical considerations and experimental data. Calculational procedures for the spectra for both thin and thick targets, the probability of photon generation and the radiative stopping power are described in detail. Evaluated results for typical media, such as water and tungsten, are illustrated and compared.

  Development of Various flash x-ray generators and their applications to high-speed biomedical radiography are described. Six types of high-voltage pulsers are as follows : 1. a single-pulse generator having a gas gap used for the diode tube, 2. a single-pulse generator utilizing a gas gap used for the triode tube, 3. a repetitive pulser for the diode tube with a repetitive frequency of less than 50 Hz, 4. a repetitive pulser for the triode tube with a frequency of less than 100Hz, 5. a triple-shot type having a single diode, and 6. a triple-shot type utilizing three diodes. These pulsers, in conjunction with the x-ray tubes, may be used for output voltages of less than 150kV (tube voltage), and peak currents of less than 40 kA. The flash x-ray intensity was primarily determined by controlling the condenser charging voltage and the anode-cathode (A-C) space and was reduced by insertion of metal filters. The x-ray quality became hard according to increase m the charging voltage, insertion of metal filters, and other factors. The effective focal spot sizes were determined by the diameters of anode rods, and their sizes were less than 3.0mm in diameter. These generators in conjunction with various types of timing switches for producing the starting pulses for the delayed pulse generator have many future possibilities for performing biomedical radiography utilizing their high-speed capabilities.

  A review is made of the performance of the Digital Subtraction Angiography (DSA) system.

  The temporal subtraction method is utilized to the imaging of diluted contrast material in the organ injected intravenously. However, the coronary angiography obtained through the temporal subtraction method is not feasible for clinical applications because of the motion blur of the heart.

  In order to avoid the risks of the present method of coronary artery angiography, a K edge energy subtraction method using Synchrotron Radiation is under development. Conceptual aspects of several subtraction techniques are discussed.

  Medical physics in radiation therapy (oncology) was briefly reviewed. A review of topics of interest to radiation oncology physicists was described. Topics inclued are : a brief review of oncology capital equipment -the accelerators, the simulators and the treatment planning computer ; a review of quality assurance ; absolute dose calibration ; topics in treatment planning ; and non-standard modes of therapy-particle therapy, intraoperative therapy, conformation therapy and hyperthermia.

  A new design of negative ion cyclotron for radioisotope production is described. The magnetic structure can be seen as a synthesis of solid-pole and separated sector cyclotrons. The beam is produced by an external multicusp ion source and injected axially into the cyclotron. Extraction is made by stripping on thin carbon foils, with essentially 100% efficiency. The R.F. system uses vertical, half-wavelength mode resonators of high mechanical stability, located in the valleys. The cyclotron is entirely controlled by an high level automated programmable logic controller (P.L.C.). During tests on the prototype, up to 577 μA of beam have been extracted successfully. The prototype has now demonstrated stable and reliable operation for more than two years. The new model of cyclotron is now in commercial production, with five cyclotrons already ordered.

  Nihon Medi-Physics Co., Ltd. has been producing ¹²³I with its cyclotrons since 1975. During the years, we have tried several production methods by ¹²²Te (d,n), ¹²⁴Te (p, 2n), ¹²⁷I (p, 5n) and ¹²⁴Xe (p, 2n) reaction. As a result, we have reached a conclusion that the indirect production method using ¹²³Xe-¹²³I precursor system enables the supply of high purity ¹²³I, which is essential for the nuclear medicine studies with low radiation exposure as well as clear image, and high ¹²³I yield for the supply of Na ¹²³I capsule and ¹²³I compounds (such as Perfusamine, an imaging agent for cerebral blood flow study).

  The amount of ¹²³I used annually in Japan exceeded that of ¹³¹I in 1987. If the cyclotron with high external beam current is used, the production capability of ¹²³I will be high enough for the existing ¹²³I radiopharmaceuticals as well as for new ones.

  The scattered radiation is generated by an object in medical X-ray diagnosis. It degrades the quality of an X-ray image. For a quantitative estimation of this effect, it is necessary to determine X-ray spectra including scatter as fundamental data. We have carried out the Monte Carlo simulation for a 70kV tube voltage, an object of 20-cm acrylic resin and fields of 2, 4, 8, 15 and 30 cmφ. The maximum incident angle was varied as 5°, 13°, 20° and 90° to investigate the grid effect. The object-detector distance was varied from 1 to 60 cm to investigate the Groedel effect. The results showed that scatter fractions decreased noticeably by the Groedel effect for the 2to 8-cmφ fields, but they did not decrease prominently for the 15- and 30-cmφ fields. The effect of the higher grid ratio appeared for the smaller angle of the collimator. For the 15- and 30-cmφ fields we have obtained angular dependence relations of scatter spectra, mean energies, and exposures. As a result , the larger scatter angle yielded the lower mean energy and the lower exposure. These phenomena were caused by the Compton effect. The results obtained by experiments using a plannar Ge detector, conic Pb collimators and beam stoppers coincided with the above results.

  CT images have been transferred to a radiotherapy planning system from a CT image computer by an on-line remote operation. The radiotherapy planning system and CT image analyzer, which is linked to a CT scanner with a dual-access disk, are connected by an optical link. The computer of the CT image analyzer is operated remotely by an operator console in the radiotherapy facility and CT images are transferred from a CT disk to the radiotherapy planning system on request of the radiotherapy planning physicist. The CT images are archived onto a radiotherapy computer disk without the necessity of carrying the magtape by hand. Experimental results indicate that transfer time for a 256 x 256 16-bit image was 143 sec at 9600 baud. The function of the radiotherapy planning system is improved by this on-line image transfer and has the advantage of allowing computer networking in imaging for planning and other radiotherapy procedures.