Calculation of air-kerma rate of diagnostic X-ray generators.

As one type of basic physical data related to the calculation of the construction of X-ray examination room shielding, we investigated the air-kerma rate 1 m from the source of the useful beam focus per unit current time product. Compared to the X-ray energy penetration values obtained in prior research, we obtained higher values. We found three causes for this discrepancy: (1) the X-ray tube total filtration (increasing total filtration reduces air kerma), (2) the tube voltage ripple percentage (increased voltage ripple reduces air kerma, and (3) the target angle (increasing the target angle increases the air kerma). On standardizing (1)-(3), we confirmed that our values mostly matched those obtained in past research. Consequently, when one employs the air-kerma rate that results from the consideration of (1)-(3), without pursuing a path of excessive safety, calculation of shielding under clinical conditions is possible.

[Shielding evaluation of lead-free board for diagnostic X-rays].

For physical foundation data used in the shielding calculation of structural facilities such as a radiation room, there are air kerma transmissions concerning the thickness of shielding objects, and half value layers and tenth value layers concerning a greatly attenuated wide X-ray beam. Accordingly, we evaluated the above-mentioned items with a lead-free board, which is mixed sulfuric acid calcium and barium sulfate with equiponderance for the amount of sulfuric acid calcium included in the usual plasterboard. Permeability in NCRP Report 147 is expressed by 3 parameters, α, ß and γ, and shielding objects x. It showed that it corresponds to the measurement point and permeability curve with parameters, α, ß and γ obtained by nonlinear regression analysis. Furthermore, we calculated the half value layer and tenth value layer concerning the greatly attenuated wide X-ray beam. The evaluated lead-free board, used in this examination, is useful as the shielding material for the diagnosis X-ray and, moreover, the partition wall materials are hard enough, with a board that is even heavier than the usual plaster board. Besides, the use of lead-free materials is friendly to the general environment.

Radiosurgical treatment planning for intracranial AVM based on images generated by principal component analysis--a simulation study.

BACKGROUND: One of the most important factors in stereotactic radiosurgery (SRS) for intracranial arteriovenous malformation (AVM) is to determine accurate target delineation of the nidus. However, since intracranial AVMs are complicated in structure, it is often difficult to clearly determine the target delineation. PURPOSE: To investigate the usefulness of principal component analysis (PCA) on intra-arterial contrast enhanced dynamic CT (IADCT) images as a tool for delineating accurate target volumes for stereotactic radiosurgery of AVMs. MATERIALS AND METHODS: IADCT and intravenous contrast-enhanced CT (IVCT) were used to examine 4 randomly selected cases of AVM. PCA images were generated from the IADCT data. The first component images were considered feeding artery predominant, the second component images were considered draining vein predominant, and the third component images were considered background. Target delineations were first carried out from IVCT, and then again while referring to the first and second components of the PCA images. Dose calculation simulations for radiosurgical treatment plans with IVCT and PCA images were performed. Dose volume histograms of the vein areas as well as the target volumes were compared. RESULTS: In all cases, the calculated target volumes based on IVCT images were larger than those based on PCA images, and the irradiation doses for the vein areas were reduced. CONCLUSION: In this study, we simulated radiosurgical treatment planning for intracranial AVM based on PCA images. By using PCA images, the irradiation doses for the vein areas were substantially reduced.

[Evaluation of non-lead board as X-ray protective material].

For security, boards containing lead are commonly used to partition off rooms adjacent to radiation facilities. From the viewpoints of environmental safety and of material recycling during the process of remodeling or repair, however, the trend is toward avoiding the use of lead-containing radiation-protection board. Consequently, we developed a lead-free board(W 910xH 1820xD 12.5 mm)composed of a mixed material incorporating calcium sulfate and barium sulfate to be used as a partition at a diagnostic X-ray institution. The mass attenuation coefficients of the lead-free board were lower by about 12% and 60% for energy ranges of 25 approximately 37 keV and 38 approximately 41 keV, respectively, as compared with those of lead. Lead equivalents for the newly developed board(12.5 mm thickness)were 0.87+/-0.01 mmPb at 100 kV tube voltage, 0.60+/-0.01 at 125 kV, and 0.47+/-0.01 at 150 kV. A double-layer lead-free board proved to have enough shielding ability even at usual photographic frequencies.

Obtaining location of I-125 seed sources for the prostate brachytherapy.

Treatment planning for ultrasound-guided transperitoneal I-125 permanent prostatic implants is a time consuming task, because this treatment uses many seeds (e.g. 50-80) and there are many solutions (seed positions) for optimizing the dose distribution. In conventional treatment planning for brachytherapy the locations of sources are usually input into a computer manually with reference to two X-ray films. We use so many sources in this treatment that we can hardly obtain accurate location of each source. That is, the identification of each seed with two X-ray films is very difficult. Even though we can use X-ray CT images for deciding on the source position, there are artifacts due to the high attenuation material. This paper proposes a method for obtaining accurate locations of radioactive sources from some projection data (e.g. RPO 60, 40, 20, LPO 60, 40, 20 and 0 deg.) with a reconstruction method. In our method for obtaining actual source positions we use an iterative image reconstruction technique. The results obtained by experiments with a simple prostate phantom and the RANDO phantom showed that the locations of dummy seeds were accurately decided with a reconstructed image by six or seven projection data.

[Visualization of intracranial arteriovenous malformation using multivariate analysis].

Intracranial arteriovenous malformations(AVMs) are composed of native deformed vessels where arteries and veins are directly connected in the absence of capillary vessels, and have a complicated three-dimensional(3D) shape. The purpose of this study was to define precisely the location of AVM areas for stereotactic irradiation. The proposed method used a sequence of dynamic X-ray CT images with contrast and opaque media. We analyzed these images by a principal component analysis(PCA) method and extracted component images: artery, vein, and background images. Then we made a fusion image with these three images and displayed the AVM areas. Results showed that the proposed method could identify the physiological location of these AVMs areas. Furthermore, we reconstructed 3D fusion images using two-dimensional component images extracted by the PCA method.