The three-dimentional therapeutic program method using a pass-through image, target volume and radiation information based on Beam's eye view on a CT image has often been used recently. However, when carrying out the therapy planning, it is indispensable to evaluate in advance its geometrical repeatability, and positioning error accuracy as well. There has been no phamtom complying with such a purpose in the past. This information describes the accuracy used to evaluate the phantom for carrying out geometrical repeatability, positioning accuracy and verification by radiation. With this phantom, we were able to make an accuracy evaluation (such as laser projector and RT/CT simulator), other daily operating checks and quality control as well as the accuracy control of the radiation information by Beam's eye view.
The new type orthochromatic film contains more of a bluish color than regular film does. The difference of the film base color has been estimated as the difference in the photographic density. Each film maker has its own color and the quantitative analysis of various types of film has not fully studied yet. In this paper, the color coordinates and color differences of three types of film were studied were evaluated using CIE (Commission International de l'eclairage) 1931 standard colorimetric system. The cause of color differences cannot be explained by photographic density or luminosity. Therefore, color differences were estimated using CIE (1976) L^*a^*b^* △Eab. The color differences shown by this method were paralleled with the degree of the visual evaluation. △Eab=1.63 was the lowest threshold in human visual sensation. △Eab=2.88 was a threshold of color differences which most people could realize. To indicate film color, CIE (1976) L^*a^*b^* uniform color space, which can show color differences by the distance between two points, was more useful than the CIE (x, y) chromaticity diagram.
Current practices for patiant safety control in radiological diagnosis involve may problems. For solving of these problems, we have to bear in mind that the mental and physical capacity of patients tend to be limted during radiological testing. When radiography is performed using a general X-ray device at a source table distance (STD) of 100cm, the patient's head can touch the X-ray tube housing during position adjustment on the stand (up and down adjustment) or the patient is made to take an unnatural posture during body positioning. With this in mind, we carried out a questionnaire survey about SID. This survery disclosed that more than 92% of the institutions have adaped 100cm STD. We then conducted a three-dimensional analysis of a patient's posture and motion by video taping patients during positioning on an roentgenographic table. This analysis revealed that the adoption of the 120cm STD resulted in less contact between the patient's head and X-ray tube housing, less of a unnatural body position and less time required for positioning adjustment when compared to those at 100cm STD. These results indicate that the current STD (100cm) is not suitable for safe and smooth adjustment of the positioning of a patient's body of an roentgenographic table. We examined the optimum STD, taking into consideration the dimensions of patient's movement and posture during an X-ray examination.
The effect of radiation treatment depends upon doses delivered to the region of both the tumor and healthy tissue. Therefore, the most important factors for successful of the radiation treatment is not only the accuracy of the dose in the target volume but also the dose in the tissues surrounding the tumor. ICRU Report 24 recommends that the dose accuracy at the target volume should be within 5% of uncertainty. However, the radiation treatment process contains several steps such as clinical examinations, patient data acquisition, treatment planning, etc. Each of these steps may introduce a significant uncertainty in the delivered dose. This paper discusses those factors that can cause dose uncertainty and suggests how to reduce the uncertainty to within 5%. The uncertainty in the radiation theapy process are : 1) Dose measurement at the reference point of waterphantom. This is about 5%. 2) Dose calculation due to an algorithm error. This error, without consideration of patient heterogeneity, is 6% for inhomogeneity correction. 3) Patient setup variations in daily treatment. These errors are estimated to be about 4.2%. According to our research at Aichi Cancer Center Hospital, based on the analysis of all these factors, the overall uncertainty has been estimated over 9%. To improve the above uncertainties, it would be important (or essential) : 1) to calibrate the dose monitor of the linear acceralator frequently, 2) to reduce the errors during the process of acquiring patient information, 3) to develop a treatment planning system which performs more accurate and faster dose computation with any sophisticated inhomogeneity correction, 4) to introduce special treatment techniques such as dose radiation with synchronized patient aspiration so as to insure reproducability of patient orientation, and 5) to stabilize the radiation energy of the source. By implementing the above, the overall uncertainty is estimated to be 6%.
Since three dimensional surface reconstruction (3DCT) and multi planar reconstruction (MPR) have become commonly applied to X-ray computed tomography examinations, it is clinically required to obtain multiple CT cross-sections in a short period of time. For this purpose, we have developed a helical scan method using a continuous dynamic scan, with table movement and continuous revolution high speed X-ray CT equipment that gives multiple CT cross-sections along the Z-axis. We will report the development, features, clinical use and application technique of the helical scan. We will also report other techniques using the continuous revolition high speed X-ray CT equipment, such as dynamic subtraction cine CT angiography (DSC-CTA), dynamic respiratry scan (DRS), extra ocular muscle movement scan (EOM scan) and temporal mandible joint movement scan (TMJ scan), including the video reporting system which we have developed to display and record the results.
Imatron C-100 ultrafast CT scanner (UFCT) using electron beam scanning system has been possible millisecond level scanning. The UFCT decreased motion artifacts by body motion and breathing. We indicated reduction of motion artifact by clinical experiment and test with phantoms. We know the result it is suitable for scanning of moving organs, such as the heart. The accuracy of blood flow estimation has improved significantly because high accuracy measurement was possible with high-speed scanning and increasing the sampling/scanning rates. Volume measurement for all cardiac chambers has also become more accurate because whole heart can be scanned by scanning time of 50 msec and malti-slice mode system. On other hand, it seems to improve for complexity of maintenance and operaition of it. Then, we desired to improve for automatic warm-up, simple operation, stability of out put beams, fllnness of software application. We have conducted technical evaluation of the UFCT for its benefits and problems in clinical application.
The usefulness of ultrafast computed tomography with the electron beam scanning system (UFCT) was assessed on the basis of 2 years of clinical experience. A scan time of 100 or 200 ms sufficiently eliminated motion artifacts and motion blur on organs. The UFCT scanner produced high quality images with smaller x-ray dose than conventional CT scanner. Short interscan time were also helpful to not only cardiovacular study, but also lung, abdominal and pediatric scanning. The Diagnostic usefulness of ultrafast CT scanning for acute aortic dissection, myocardial infarction, hypertrohpic cardiomyopathy, intracardiac small thrombus, coronary calcification, postoperative pulmonary complication, functional cardiac study is discussed. The results indicate that the conventional CT scanner should be improved for better quality imaging in the least possible scanning time.
Imaging time of the X-ray computed tomography has been shortened dramatically since the first generation of EMI MARK-I was invented. However, recent CT scanner still has the imaging time of order of 1 second, which is not suitable for obtaining stop-motion cross-section of the heart. In order to construct a CT with ultrafast speed, two attempts were made : One is the multi-souce and multi-detector system which is represented by Dynamic Spatial Reconstructor of Mayo Clinic and the second employs the scanning electron beam system. The latter system has been developed in Japan by Tateno and Iinuma et. al. as the X-ray microbeam scanning system called "Dynamic Scanner" and then the proposal for ultrafast computed tomography has been made in 1977 by them. Boyd of UCSF has published a paper on cardiovascular computed tomography (CVCT) using the same principle of scanning electron beam in 1979 and produced a commercial machine of Imatron C-100 ultrafast CT. There are several problems with the present C-100 scanner which is costly and large in space, but these will be solved in the future. Spatial resolution is expected to increase by a factor of two, soon. In my view, the ultrafast CT will start a new era of CT diagnosis of real-time 3-dimensional X-ray anatomy that is not possible with the present CT scanner, and will contribute siginificantly to the non-invasive detection of heart diseases, cancer and brain disorders.