摘要:

A three‐dimensional irradiation system using scatterers for lateral spreading is proposed. This system, which is applicable to proton beams, is easily achieved by ordinary techniques using a movable multileaf collimator, a variable thickness water column, and a computer for their control. Target volumes of convex shape can be irradiated in a three‐dimensional way by this method.

ISSN:0269-3127    

DOI:10.1118/1.595254

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A Clinac‐4 therapy accelerator has been modified to function also as a computed tomography (CT) scanner. We report on measurements made to calibrate the beam. 104 Bismuth‐germanate silicon‐photodiode detectors were placed in a circular arc of radius 180 cm, centered on the source, in the arrangement of a third‐generation CT scanner. With the beam collimated to a fan section and just filling the detectors, the signalS(x), obtained with thicknessxof plastic phantom, closely followed the relationshipS(x)/S(0)=exp [−(αx+βx2)], where coefficients α and β varied systematically over the extent of the beam. This result agrees with results of similar work by others. It may be explained in terms of the spectral changes that are known to be an inherent property of such beams. Expressions relating α and β to the source spectral density are derived; also estimates of the source spectral density are calculated using the method of Laplace inversion. It is shown that scattered radiation arising from the fan beam within the scattering medium does not contribute significantly to the values of α and β.

ISSN:0269-3127    

DOI:10.1118/1.595280

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Product representations are frequently used for teletherapy dose distributions. For example, the dose in a central plane is often written as the product of two factors, one dependent on the depth and the other on the transverse variable. We have answered the following question: given a (two‐dimensional) set of data, how closely is it possible to represent these data by a product of two such factors, and what factors would give a best‐fit representation? We thus have developed a quantitative test with which to judge any proposed product representation, for a given set of data. As an example, we have applied our method in analyzing the accuracy of a model proposed by van de Geijn for representing central‐plane Cobalt‐60 dose data through a product representation on decrement lines intersecting the source.

ISSN:0269-3127    

DOI:10.1118/1.595281

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Both small and irregular fields are frequently the treatment of choice in many clinical applications of electron therapy. The fields are often shaped by lead or low melting point alloy placed at the end of the cone or on the patient's surface. The dosimetry for electrons of energies of 4, 6, 8, and 10 MeV is examined with particular emphasis on very small fields for treatment such as the lip, nose, and eye and irregular fields of various area/perimeter ratios. The paper discusses the dosimetry correction due to field shaping as a function of the location of the shield.

ISSN:0269-3127    

DOI:10.1118/1.595282

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

An experimental procedure using edge response functions (ERF) has been devised to rapidly provide modulation transfer function (MTF) values for gamma camera imaging. Both camera intrinsic and system MTFs are generated. This procedure uses a simple test tool to generate the ERF which is then processed by a computer program using a cubic splines differentiation technique and a discrete Fourier transform algorithm to produce the MTF values. An analytic test of the computer algorithms as well as an experimental test using collimator data from the Bureau of Radiological Health is presented to confirm the accuracy of the procedure.

ISSN:0269-3127    

DOI:10.1118/1.595283

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

The precision and accuracy achieved in the measurement of characteristic curves for radiographic screen/film systems is quantitatively investigated for three techniques: inverse square, kVp bootstrap, and step‐wedge bootstrap. Precision of all techniques is generally better than ±1.5% while the agreement among all intensity‐scale techniques is better than 2% over the useful exposure latitude. However, the accuracy of the sensitometry will depend on several factors, including linearity and energy dependence of the calibration instrument, that may introduce larger errors. Comparisons of time‐scale and intensity‐scale methods are made and a means of measuring reciprocity law failure is demonstrated.

ISSN:0269-3127    

DOI:10.1118/1.595285

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A method for locating radioactive seeds in interstitial implants has been developed that requires three radiographic views. Spatial coordinates for the seeds are computed from the randomly digitized seed images on each of three radiographs, and information about the tube and film placement for each of the radiographs. Further, the ability to accurately (greater than 98% of the seeds within ±2.5 mm) locate the seeds does not require the use of a specialized radiographic technique; the radiographs need only represent three different views of the implant. Also discussed is the seed image matching technique that enables ambiguous seed matches to be resolved.

ISSN:0269-3127    

DOI:10.1118/1.595275

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1983.tb36187.x

出版商:Wiley    

年代:1998

数据来源: WILEY

摘要:

Isodose measurements of 4‐MV beams obtained with a Therados radiation field analyzer were found to vary significantly with the types of detector used, viz., a Physikalisch–Technische Werkstatten (PTW) ion chamber with positive and negative collecting potentials and a Therados diode detector. Suitable means of minimizing the ion chamber polarity effect are described.

ISSN:0269-3127    

DOI:10.1118/1.595276

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Data which agree with those of Falloneet al. are presented. The issue of translatinginvitroresults to theinvivosituation is also discussed.

ISSN:0269-3127    

DOI:10.1118/1.595286

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY