Cerebral magnification angiography with a intensifying screen system of the specific rare earths, has lately been introduced and been requested to discriminate more minute vascular structures. Routine vertebral magnification angiography (VMG) with the screen system provides half-axial and lateral views or sometimes antero-posterior and lateral views. However, in the half-axial and lateral views, accurate X-ray reading of the vascular system in posterior cranial fossa is in trouble. In 1973 a mento-occipital open mouth view in the vertebral angiography started at our department and since 1975 the view has been provided with a magnification and the intensifying screen system. The mento-occipital-open mouth view in the VMG, X-ray vertically projected to basilar artery and decreased overshadow of the facial bones. The demonstration of the vertebro-basilar system, especially the junction point or beginning portion of arteria cerebelli inferior posterior (PICA) was more excellent than in the routine views. The reduction in the length of the vessels was reasonablly decreased. The half-axial view longitudinally reduces the vertebro-basilar vasculo-system and the lateral view blurs the vascular portion from the stem of basilar A. to vertebral branching of the PICA because of overshadows of bilateral petrous temporalis. Clinically the author's view was effective to analise the vascular arrangement in the VMG.
In recent years, it has been an important theme for the diagnosis of pulmonary hilar cancer to evaluate whether the lesion in hilar lymph nodes and the vicinity of the hilar bronchus exists or does not. It is shown that pulmonary hilar region is from main bronchus to segmental bronchus which is separating subsegmental bronchus. It is difficult to make the optimal density for all area of the pulmonary hilar region on a same film, because there is too much difference of density between medial region under the veil of thoracic vertebra, sternum, heart and great vessels, and lateral region in conventional tomography. Therefor, a compensating filter was constructed to equalize the uneven density of pulmonary hilar region on a X-ray film. As a result, trachea, main bronchus, upper lobal and segmental bronchus were observed simultaneously and serially on a same film by using this filter. In addition, we could study the condition in the inside and outside of bronchial wall in detail, and have many informations compared with conventional tomogram. Particularly, this is an useful method to determine the range of lesion in the pulmonary hilar cancer.
In the study of possible reduction in irradiation dose to patients during medical treatments, the following two methods can be considered : (1) To obtain absorbed doses for each part of a body in diagnostic X-ray examinations. (2) To obtain data on factors such as the tube voltage which may affect patient dose. There are a number of reports both at home and abroad concerning the above (1), but very few reports are available concerning the above (2). Moreover, most of them are on fragmentary aspects of each factor and no systematic reports have been made. For this reason, we have taken up, as factors affecting the patient dose, the field size, the tube voltage, and by checking them again, we wanted to obtain some systematic data. Our aim has been fully attained by conducting an experiment. In the ICRP's Publ. 26 issued last year, the idea of the critical organ which had not been fully elucidated in the Publ. 9 was abandoned. As a result, assessment of the irradiation doses has become more rational and the total risk for an individual was obtained. In Japan, the idea proposed in the Publ. 9 is adopted. Therefore, in this paper, we will raise some questions regarding the assessment of the irradiation doses, pointing out at the same time the rationality of the idea put forward in Publ. 26.
Comparisons of exposure dose to the patient of three types of oral x-ray apparatus (Dental, Panoramix, Orthopantomograph) were made. The exposure doses to the regions of incior, molar, eye (lens), thyroid gland, cervical spine and gonad were measured using Radocon II type dosimeter, T.L.D. and head phantom. Differences of exposure dose were found in three types of oral x-ray apparatus. After then improvement of aparture and investigation of sensitive materials and filter were made. Selection of the oral x-ray apparatus should not be done by exposure dose but by need of diagnosis.
The NaI (Tl) scintillater detector of a head CT scanner (Hitachi CT-250) in our hospital has recently been replaced by BGO sintillater. The reason for the replacement was to exclude the size dependence of a CT scanner. An Alderson Catphan has been used to evaluate the performance of the two different detectors. Half value layers were measured under usual scanning condition of 120Kv, 30mA tube voltage with additional filter of 0.1mm Cu+0.5mm Al. The results were as follows : 7.5mm H.V.L.Al for NaI (Tl) scintillater, and 7.1mm H.V.L.Al for BGO sintillater. Half value layer for NaI (Tl) detector was, therefore, significantly thicker than that for BGO detector. In addition, CT numbers of water were measured for both detectors. The results showed that the CT numbers of water were decreased as the tube voltage increased in NaI (Tl) scintillater. The results were opposite in BGO scintillater. In conclusion, the size independence and linearity has been improved in BGO scintillater detector.
In the Screen-Film system, it is inevitable problem that deterioration of granularity with rise of relative sensitivity. The purpose of this study is phenomenon. For this purpose chose the MTF, RMS, Relative Sensitivity, Fog, γ, and Sensory Evaluation, as parameters for evaluate the Character of each element which composed the image, and calculate the correlation between physical specific quality and sensory evaluation, or the correlation between each Physical specific quality.
Artifacts and image degradation in CT ofen occures when materials of extremely high or low radiographic density and smaller lesions than a slice thickness exist. In this paper, to reduce artifacts caused by mechanical and technical problems we tried to obtain the best slice thickness by making experiments upon the relationship between attenuation values and slice thickness which were changed by narrowing the width of collimators of both a x-ray tube and a detector sides of EMI scanner CT-1010. As a result of these experiments, CT images of good quality almost free from artifacts were obtained experimentally and clinically when scans were performed with a slice 5mm thickness.
The most important factor needed for a routine service in radiotherapy is high order reliability of radiotherapy units. The failure analysis based on detailed maintenance records and provision of emergency repairs were required to minimized accidental trouble of machines. In this report, the factors in relation to machine reliability such as failure rate, mean time between failure, etc were described. The data used were eleven years maintenance records of betatron and linac in our hospital. Furthermore, the results of survey for 7 linacs and 5 betatrons in 11 hospitals were reported. The expected average life time of main parts such as magnetron, electron gun and doughnut were estimated. The results of failure analysis revealed that average falure rate were 1/1.5 months in linacs, 1/5 months in betatrons respectively. For high order reliability of radiotherapy machine, it is reasonable to minimize the tracing time for trouble points which were large proportion of emergency repair, and for this, the flow diagram would be useful agent. The precise and large amount of data concerned with maintenance will be desirable for the accurate estimation of machine reliability in user's side, and for the preventive maintenance. Furthermore, a fixed form of maintenance record would be better.
1. For dosimetry in radiotherapy, it is important to check the stability of the dosimeter and calibrate it. A standard source is indispensable for the former and substandard dosimeter is necessary for the latter. 2. The monitor dosimeter should be frequently calibrated by the reference dosimeter. The consistency check value of the monitor sensitivity was measured, that of the Betatron of Kyushu university hospital was within ±15% 3. Modulation transfer functions (MTFs) of the global and the cylindrical ionization chamber of the same diameter was calculated. The former is superior to the latter. 4. The dose distribution of the telecobalt unit depend on the size of the source and source-diagram- distance (SDD). The dose distribution of the varying SDD was calculated from the optical transfer function of the cobalt-60 source using inverse Fourier transform. 5. The MTF of the cobalt-60 source measured by the so-called Segment Method is almost equal to that obtained from the calculation.
In order to perform safety operation of the radiotherapy apparatus and to secure accuracy in positioning patients and in setting up of the radiation beam, a proper checking and maintenance schedule is necessary. Such a schedule is described here briefly, and also mechanical or electrical structures designed for securing the safety and accuracy or eliminating inadequate operation are commented especially on the treatment table and accessories, such as a wedge filter, a pointer, and a device for observing patients.