The characteristic curve of widely used X-ray cinefilm is thought not to be represented precisely when routinely measured by a sensitometer. The main reasons are as follows; the exposure time of the sensitometer is longer than that of the actual exposure time of X-ray cineradiography, and the secondary emitted fluorescent spectrum from the image intensifier (I.I.) does not correspond to the green-filter which is used for simulation. The purpose of this investigation was undertaken to solve these problems using a photo electronic flash (strobe) as the light source which can obtain a shorter flash exposure time than a routinely used sensitometer for X-ray cineradiography. We also investigated the changes of the spectral transmission rate of the green-filter which influenced the characteristic curve when exposed under various kinds of green-filters. The following conclusions were obtained. 1. The flash time of strobe was noted as 2 msec, and it emitted enough light quantity to draw up the characteristic curve. 2. The high voltage direct current was found to be an adequate power supply for strobe flash. 3. The higher reproducibility of the light flash was obtained using constant charging time of the strobe. Also, it could measure average photographic density of the film under multiple exposures. 4. The spectrum distribution of the green-filter must coincident with the fluoresence wave-length of which is a secondary emission of I.I. 5. The characteristic curve which is drawn by our method is closely like that of the X-ray ND method.
Several approximation methods for photon beam dose calculations have been developed by many researchers. Although the currently used methods of radiation dose calculation are practical, it is recognized that these methods are not accurate enough when 3-dimensional anatomic information of shape and atomic content have to be considered. In this paper, we will briefly review the most commonly used dose calculation algomithms and report the results that evaluated the accuracy of does computations using these algorithms. The accuracy is compared with both calculations and measurements on beam central axis for cobalt-60 gamma-rays and 10MV photon beams for various geometries and field sizes. The equivalent TAR method gives good agreement between measured and calculated dose for heterogeneous three layered phantom configurations irradiated by 10MV photon beams. The power law TAR method is also good for cobalt-60 gamma-rays when the extent of the lung-equivalent material heterogeneity is larger than the area of the beamn. The ratio TAR method which doesn't take into account the scattered radiation is inadequate in heterogeneous medium.
This paper, summarizes experiences in the use of the mammograph for the mass screening of breast cancer. The exposure dose per experience was only 1/8.4 (0.21mSv) that of conventional mammography. Application to 243 persons resulted in 95.6% (43/45 patients) of TPR, 57.1% (113/198 patients) of TNR and 1.7% (2/115 patients) of false negative. Although the authors consider that the mammograph has a bright future, a few points for improvement follow herein. It was also confirmed that, in order to promote the accuracy of mass screening of breast cancer, the most important points are to promote photography techniques and decipherment of X-rays.
When improving the accuracy of the radiation dosimetry for the radiation therapy, it is required to understand correctly the characteristics of a variety of dosimetric methods and their accuracy. The followings describe the importance of the traceability of the therapy level dosimeter, and the accuracy and characteristics of radiation dosimetry of the JARP level dosimeter, Micro-chamber, Film, Diode and TLD together with precautions to be taken for actual dosimetry. Furthermore, the analysis pertaining to the physical characteristics of the tough water (WE-211) specially developed by Hiraoka and the group was also carried out.
The X-Ray measurement in diagnosis reasion consists of the following two parts. 1. Measurement of Exposure 2. Measurement of X-ray Quality 1. Exposure measurement The diagnosis X-ray, though its accumulated exposure in Radiography is rather small, is characterized by its instantanously high exposure rate and its comparatively low energy. These facts present the problems of ion recombination loss correction in an ionization chamber and of energy dependency of correction by a chamber wall thickness. Recently the X-ray out-put is very high and we must pay enough attentions to the ion recombination loss in an ionization chamber. 2. Quality Measurement We usualy measure X-ray quality by the method of the Al atenuation curve or by the energy spectrum by pure Ge-semiconductor detector. Recently the new concept of the Dose-Equivalent has bean introdused in the field of Radiation Control. The X-ray energy spectrum measurement is necessary for the Dose-Equivarent. Then X-ray quality measurement has become very important.
It is essential to measure the dose of radiation fields and the conditions of contamination with radioactive materials for a suitable radiation control. Some people often emphasize the importance of the measurement in radiation control by the word "No measurement, no control". It is quite questionable, however, whether adequate technique and knowledge in measurement is employed for radiation control in medical facilities, for most people following the radiation control in these facilities are working as a side job. Appropriate techniques to guarantee the reliability of measurement as well as suitable low-cost easy-handling equipment should be developed for the measurement in medical radiation facilities. At the same time, we must ponder on the purpose of measurement in radiation control; what kind of quantities should be measured with what extent of reliability for the purpose.
ETL exposure standards for X-rays and it's beam qualities for calibration of measuring instruments are described. Several problems concerned to X-ray spectra are discussed. National standards for high energy X-ray, neutron measurement, beta-ray measurements and radioactivity measurements are introduced briefly. ETL services relevant to establishing traceability to the national standards for ionizing radiation are described.
In recent years, computer technology has been introduced to control meny units of radiotherapy, and each of the units frequentry has a close relationship with the other units. Consequently, the radiotherapy system is now considered to be a totalsystem including all over the units and the apparatus that is concerned with radiotherapy. However there is no dout that the radiotherapy system still has meny probrems concerning precise dosimetry, working sufficiency, system capability, economy, security etc. At this point in 1990, it is intresting to discuss on radiotherapy systems from three different stadingpoint of view, namely, as a radiotherapist, a radiotechnologist and an engineer the opinion of these three authorities in their field will provide usefule suggestions on our works.
In these days, technical inovations of medical accelerators including especially linear accelerators have much improved accuracy and repeatability of radiation delivery systems. On the other hands, a PACS which deals with storing and archivs of advanced medical diagnostic images by electronic comunication systems has been remarkablly improved and entered its routine use. These technologies are studied and become made good use of for the purpose of three dimensional radiation treatment planning systems and high energy X-ray real time imaging and its image prossecing veryfication systems. When we discuss radiotherapy systems, not only technical and academic issues but also economic, safety and confortable system development for patients should be taken into account. As the results, the improvements of reliability and safety should be primary discussed. Accordingly computer and three dimensional imaging applications and IEC standards become to play important role. These improvements affect the radiation oncology and the interdisciplinary and multimodal radiotherapy becomes realistic and ecconomical. In addition, recent characteristic technical issues are sumerized and tried to give appropliate solutions including a three dimensional radiation delivery system.