PubMed Health⌕ Search

Biomedical subjects

K Tabushi

Publications and source records attributed to K Tabushi.

At least 19 recordsLinked to original sources
PubMed1995

[Determination of source position for four radiography systems with orthogonal projections in brachytherapy].

Four configurations of two X-ray tube positions are available for determining the position of a point using two orthogonal films. For each configuration, there are many formulas for calculating the coordinate of a point: the least squares methods with and without physical meaning, such as six sets of geometrical solutions, an approximation method with constant magnifications and so on. It is troublesome for a person in charge of treatment planning to directly derive a formula or select an appropriate formula from numerous ones for the four configurations. Thus, a method to easily apply the published formula for a configuration to the other three configurations is described in simulations and a clinical case using rotation matrixes of the right-handed coordinate system. Each diagonal element of the rotation matrixes is 1 or -1, and the other elements are 0.

Brachytherapy↗
PubMed1995

[Techniques for determining position from more than two radiographs intersecting at arbitrary angles in brachytherapy].

The least squares method and geometrical solution for calculating position were used in the two-projection method. Five coordinate systems were defined as a normal system, image system on film intersecting the beam central axes at an arbitrary angle and the projection, virtual coordinate and virtual image coordinate systems with beam central axis as one of the three coordinate axes to determine the geometrical relationship between a point and image on the film. Normal coordinates of the point were calculated by six geometrical solution sets and two forms of the least squares method using the rotation matrixes of the coordinate systems. One least squares method solves simultaneous nonlinear equations, and the other derives a strict solution from simultaneous linear equations. The latter least squares method has little physical meaning and is not as useful as the former. Although the former has physical meaning, the iterative approximation method should be used to determine position since a strict solution cannot be obtained directly. By these least squares methods, position is determined with less error using the projections at more than two focal spots.

Brachytherapy↗
PubMed1993

[Determination of the point position for brachytherapy from the shift-projection method using the least squares method and geometrical solutions].

We have derived formulas by the least squares method and six sets of geometrical solutions for calculating the position for brachytherapy from shift-projection images on one or two films. There are four types of expression for each coordinate in both methods, the shift-film technique with double exposures on a film and the stereo-shift technique with two films. Some geometrical solutions for the shift-film technique are equal to well-known conventional formulas. In the case of the stereo-shift technique, each conventional formula for the two coordinates is equal to the mean of the two geometrical solutions of each coordinate, and the one for the other coordinate is equal to one of the geometrical solutions. Formulas for the shift-film technique can be easily reduced to those for the stereo-shift technique. The error of the position calculated by the least squares method was the smallest among all the formulas for the shift-film technique in simulation.

Brachytherapy↗
PubMed1990

[Determination of the point position from two orthogonal X-ray photographs using least squares method and geometrical solutions].

Six sets of solutions for calculating the position of an interest point were obtained geometrically using four measured image coordinates on two X-ray photographs orthogonally projected. When the image coordinates had no error, all the solutions gave the same position without error. When an error occurred, the calculated positions differed from each other due to the propagation of error. Some solutions could not be used for this determination owing to a large propagation of error. Under conditions similar to those of clinical practice, the ratio of maximum error of position calculated by the six geometrical solutions to minimum error was about 426. The least squares method that we proposed gave results with less error. When one of the image coordinates could not be measured for some reason, the least squares method became automatically equivalent to one of the six geometrical solutions.

Image Processing, Computer-Assisted↗
PubMed1989

[Experiences in clinical application of an automated calculation system that determines the optimum intracavitary irradiation condition in the treatment of carcinomas of the uterine cervix].

An automated calculation system that determines the optimum intracavitary irradiation condition for treating carcinomas of the uterine cervix has been developed on the basis of the Manchester system. Using Vax-11 computer, the system has been successfully applied in treating 105 patients since December, 1984. Trouble with the system almost occurred during its use in the first year of its clinical application. One problem related to the method of calculation, which was quickly settled, and the other was mainly a human error. The calculation system has proven especially useful for radiotherapists.

Brachytherapy↗
PubMed1988

A method for calculating the optimum irradiation condition for intracavitary radiotherapy using quadratic programming.

A method of calculating optimum irradiation conditions for intracavitary radiotherapy using quadratic programming has been formulated and then modified for practical application. The allowable range of obtained dose, which is usually fixed in advance, is automatically computed to be as small as possible. The variance of the product of the activity and the irradiation time of the tandem source is also minimised to avoid the occurrence of cold and/or hot spots. Optimum irradiation conditions for conventional intracavitary radiotherapy of carcinoma of the uterine cervix were obtained on the basis of isodose curves passed through the points A of the Manchester system. Those for carcinoma of the other organs and special cases of carcinoma of the uterine cervix can be determined after consideration of the tumour state.

Brachytherapy↗
PubMed1985

[An analysis of tumor status of stage 3 carcinoma of the uterine cervix according to Cox's theory].

Four hundred and eighty three cases of primary stage 3 carcinoma of the uterine cervix which were treated at the National Institute of Radiological Sciences were analyzed with reference to the tumor status at the first examination, using Cox's proportional hazard model. Five prognostic factors, i.e. growth type of tumor, size of tumor at portio, size of uterus (including cervix and body), degree of tumor infiltration of parametrium and degree of tumor infiltration of vaginal wall, were considered. A coefficient of correlation, parameters of a hazard model, relative risk and survival functions were calculated with a program developed by us. The coefficient of correlation between the size of the uterus and the size of the tumor at the portio or the parametrial infiltration was about -0.5. Other combinations of prognostic factors indicated only a small correlation. When five prognostic factors were analyzed independently, the size of the uterus was found to have the greatest influence on the patient's prognosis and infiltration of the vaginal wall had the least. A combination of prognostic factors was selected according to the criterion of small correlation with each other. And then, the combination was evaluated for prognosis and to find the level of parameters under the asymtotic normal distribution. The best combination consisted of a growth type of tumor, a size of tumor at portio and tumor infiltration into the parametrium. Parameters of each prognostic factor which were calculated simultaneously from marginal likelihood were 0.236, 0.534 and 0.151, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1982

[RCT image study by angular interval of sampling].

A multi-purpose gamma camera system which had 2 detectors of opposed position and was capable of radionuclide computed tomography (RCT) imaging was installed in Division of Nuclear Medicine, Chiba Cancer Center Hospital. In this study, the variance of RCT image due to the angular interval of sampling was analyzed. The full width at half maximum (FWHM) and full width at tenth maximum (FWTM) of point source were almost same for all sampling intervals investigated. The distortion of RCT images with uniform activity source could not be detected even for larger intervals. When the RCT images were obtained using a phantom contained 3 line sources and a bar phantom for RCT which were located at right angle with the plane of reconstruction, the images did not change between 1 degrees and 6 degrees of sampling interval, but for 9 degrees or more the distortion of images occurred explicity. For our system, sampling interval of 2 degrees was predicted from the theorectical calculation considering both resolution and statistical noise. But, results from the phantom studies of present work showed that sampling interval of 6 degrees was sufficient to reconstruct RCT images without distortion, and could be applicable to dynamic RCT images.

Models, Structural↗
PubMed1981

[An evaluation of characteristics of motion corrector attached to a gamma-camera (author's transl)].

The characteristics of the motion corrector system attached to LFOV gamma-camera (Searle) was evaluated using a T-shaped plane source and point sources. The random movement without rotation of a T-shaped plane source was successfully corrected. However, rotating motion of the plane source was not corrected. When a point source placed on a rotating table, ring images were obtained. When motion corrector was used, the radius of ring images was increased with the increase of rotating speed and it was decreased with the increase of radioactivity of the source. Line images were obtained when point sources were placed on a shaker, which caused linear periodic motion of the sources. The use of the motion corrector reduced the length of line images.

Humans↗
PubMed1981

[Utilization of minicomputer for the quality control of radioimmunoassay (author's transl)].

In our nuclear medicine laboratory the quality control (QC) of radioimmunoassay (RIA) has been performed along the line of WHO program for standardization and quality control of RIA. The QC procedure was automated using a minicomputer in order to avoid tedious and time-consuming hand processing. The program was written with BASIC language. The counts of radioactivity measured in autowell counters are regarded in PTR, through which the data are read into a minicomputer (Scintipac 200). After informations on the concentrations of standards are registered through keyboard of CRT, the data processing is performed including curve fitting, dose calculation and quality control. As the indicators for QC response error relationship (RER), standard curve, precision profile and QC chart are displayed on CRT. On the basis of rejection criteria using these indicators, bad assays are identified to be omitted from reporting. The subroutine installed in the minicomputer system is used for the storage of data on QC samples in each assay, which are used for construction of QC charts. The use of a minicomputer enables implementation of QC of RIA on routine basis with ease and speed.

Computers↗