ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1980.tb36142.x

出版商:Wiley    

年代:1998

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1980.tb36143.x

出版商:Wiley    

年代:1998

数据来源: WILEY

摘要:

This review is concerned with the use of video‐fluoroscopic images in diagnostic radiology. It particularly emphasizes the potential of such images for performing quantitative procedures such as used in pulmonary and cardiac assessment, evaluation of contrast differentials, and tomographic (including CT) applications. This article also attempts to determine limitations, capabilities, and required developments for both the present and future hardware systems. Most importantly this review attempts to assess the present state of the art and to analyze the reasons for the limited application of such techniques in current radiology operations.

ISSN:0269-3127    

DOI:10.1118/1.594747

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A conceptual design is presented showing that, by judiciously choosing the beryllium target thickness and the backstop material, improvements can be achieved in dose–rate, skin sparing, and penetration of neutron beams generated by the same proton accelerator.

ISSN:0269-3127    

DOI:10.1118/1.594748

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Results are presented of measurements of skin sparing, penetration and total dose per unit of incident charge for various target thicknesses and filtrations for a neutron beam generated by 42 MeV protons on beryllium. These results are contrasted to predictions outlined in a previous paper. The differences from these predictions are attributed to the contribution of low‐energy neutrons produced by the residual proton beam in the thick copper target backstop.

ISSN:0269-3127    

DOI:10.1118/1.594749

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Neutron beams for therapy always contain some γ ray contamination that varies with depth and with distance from the beam axis. The problem therefore arises how the varying γ ray contribution should be accounted for in dose specification. Not infrequently a “total effective dose”DEis quoted that is equal to the neutron dose plus the γ ray dose divided by a constant weight factor τ. On general biophysical considerations this appears to be not a valid approach since it must be assumed that τ decreases with increasing dose. The nature and the magnitude of this dose dependence is derived in the present article. Application of the results to actual doses per fraction and to factual γ ray to neutron ratios demonstrates that the dose dependence of τ has, in fact, very minor influence on the numerical values ofDE. Utilization of a constant value τ is therefore satisfactory in practice.

ISSN:0269-3127    

DOI:10.1118/1.594743

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Neutron and photon energy spectra were measured in different depths and lateral positions in tissue‐equivalent phantoms exposed to a therapeutical 14.1 MeV neutron beam. Intensity weighted mass energy absorption coefficients were derived for application in ionization chamber dosimetry in mixed neutron‐gamma fields. The resulting relative depth doses show that on the beam axis for depths in excess of 20 cm, gamma radiation contributes with more than 10% to the total dose; off the axis outside the direct beam neutron and gamma doses are comparable. The differences between these doses and those neglecting the spectra distribution increase with depth and with the distance from the beam axis.

ISSN:0269-3127    

DOI:10.1118/1.594744

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Although electron backscatter has been a subject of investigation for many years, both theory and experimental data are sparse. This article examines the available data and shows that a large percentage of both the theoretical and experimental values fit an empirical relationship for a large range of electron energies. This relationship appears to be valid both for β‐ray spectra and monoenergetic electrons. The empirical relation describing the intensity of electron backscatter is also valid over the entire range of atomic elements. The relationship proposed is that the backscatter of electrons is proportional to the log (Z+1). Effective atomic numbers of compound and mixtures arrived at using this relationship can be used to predict backscatter coefficients for these.

ISSN:0269-3127    

DOI:10.1118/1.594750

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Causes for the discrepancy noted by Grantet al. between the in‐water and in‐air calibration of60Co are discussed. Data are presented from measurements with a set of ionization chambers with thimbles of 0.5, 1.0, and 1.5 cm outside radii. These data include measurements of percentage depth dose, backscatter factors, and displacement factors. The results show that the discrepancy noted by Grantet al. is caused by a combination of small errors both in depth dose data and in the displacement factor incorporated intoCλ.

ISSN:0269-3127    

DOI:10.1118/1.594751

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The performance characteristics of prototype grids constructed with 0.1‐mm‐thick Ta strips were investigated. Significant improvement in scatter cleanup was noted in comparison to commercially manufactured grids, which are constructed with 0.04–0.05‐mm‐thick Pb strips. Highly efficient scatter rejection, approaching that of slit radiography techniques, may be possible using crossed grids constructed with 0.1‐mm Ta strips. By constructing a grid from a crossed pair of linear grids and moving these grids at right angles to each other, grid lines can be eliminated from crossed grid images.

ISSN:0269-3127    

DOI:10.1118/1.594752

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY