摘要:

Microdosimetric measurements were made for the neutron therapy beams at the University of Chicago and at the Cleveland Clinic with the same geometry and phantom material using the same tissue‐equivalent spherical proportional counter and standard techniques. The energy deposition spectra (dose distributions in lineal energy) are compared for these beams and for their scattered components (direct beam blocked). The model of dual radiation action (DRA) of Kellerer and Rossi is employed to interpret these data in terms of biological effectiveness over this limited range of radiation qualities. The site‐diameter parameter of the DRA theory is determined for the Cleveland beam by setting the biological effectiveness (relative to60Co gamma radiation) equal to the relative biological effectiveness value deduced from radiobiology experiments and clinical experience. The resulting value of this site‐diameter parameter is then used to predict the biological effectiveness of the Chicago beam. The prediction agrees with the value deduced from radiobiology and clinical experience. The biological effectiveness of the scattered components of both beams is also estimated using the model.

ISSN:0269-3127    

DOI:10.1118/1.595897

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

To select the optimum therapeutic neutron beam available from a CS30 medical cyclotron (manufactured by the Cyclotron Corporation, Berkeley, California), central axis depth dose data and output dose rates were compared for the bombardment of beryllium with either the proton or deuteron beams available from the machine. The effect on these parameters of filtering the beams with either pure polyethylene, polyethylene loaded with 5% boron, or polyethylene loaded with 10% lithium was studied. A 4‐cm, 10% lithiated filter used with a 26‐MeV proton beam was selected for therapeutic use. Buildup curves, beam profiles at several transverse planes for different field sizes, and comparison of beam profiles with60Co are given.

ISSN:0269-3127    

DOI:10.1118/1.595898

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

An epithermal neutron beam has been designed and tested at the Georgia Insitute of Technology's 5‐MW Research Reactor. The prototype facility consists of aluminum and sulfur disks in a tangential beam port for fast neutron filtration. A cadmium sheet at the port exit removes the thermal neutrons from the transmitted beam, leaving an intensely epithermal neutron beam spanning five energy decades, each contributing to the flux demanded by boron neutron capture therapy. The thermal neutron flux generated by the incident epithermal neutrons in a polyethylene head phantom peaks at a depth of 3 cm and remains above the incident thermal flux to a 7‐cm depth. The beam thus provides the penetration required for treating deep‐seated gliomas. Photon contamination in the prototype facility is high, and a number of basic modifications are proposed for reducing it to safer levels.

ISSN:0269-3127    

DOI:10.1118/1.595899

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

We describe calculations of the energy loss, range, stopping power, multiple scattering, and other related properties of a high‐energy heavy‐ion beam at any one of a set of beam line elements. A beam line element (e.g., any beam modification, detection, or control device) is characterized by its thickness, areal density, aperture, and function. The loss of multiply scattered particles to any finite‐aperture detector is calculated in the small‐angle approximation, and the position of the Bragg peak, as given by particles stopping in the second of two ionization chambers used for Bragg curve measurements, is estimated. A general purpose computer program,propagate, has been written to allow addition, deletion, and modification of the beam line elements used in the calculation and to provide a convenient means of repeating such calculations for arbitrary beam lines. Calculations and experimental measurements are compared and found to be in satisfactory agreement.

ISSN:0269-3127    

DOI:10.1118/1.595900

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Regional blood flow measurements were analyzed using a two‐compartment model. The distribution of injected tracer between blood and tissue was assumed to be in equilibrium only at the beginning of the experiment. Equations for the determination of the partition coefficient of injected radionuclides fromin vivomeasurements were derived. These equations can also be used for estimation of the relative blood content of a tumor or an organ. The results were applied to experiments, where three diffusible radionuclides were injected simultaneously into patients with diagnosed tumors.

ISSN:0269-3127    

DOI:10.1118/1.595901

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A discussion of the thermodynamic aspects of a relatively new treatment method for giant cell tumors of the bone is presented in this paper. The advantages of implanting methylmethacrylate acrylic bone cement into a curetted tumor site are briefly discussed and placed in perspective relative to more prevalent surgical treatments. As the bone cement self‐heats while curing, the possibility of heat necrosis in the bone exists. However, the damage due to heat may be beneficial in reducing the rate of tumor recurrence. A thermodynamic consideration of the treatment situation appears to be warranted. After a general introduction and a brief literature review, the theoretical thermodynamic equations are developed. Once the basic equations for the heat transfer from the cement or the bone are derived, there is then a discussion of the various characteristics of bone and methylmethacrylate crucial to the analysis, such as, thermal conductivity, specific heat, density, and heat generation parameters. Finally, in order to reduce the theory to a form which may be used practically, the equations derived are written in terms of finite‐difference equations, which approximate them numerically. Different equations are written for each type of heat transfer condition encountered in the cement–bone system as spacial variances in material and geometry occur. The equations derived may be used to model the system allowing one to predict the time‐dependent temperature distribution in bone during the curing of acrylic cement. Using computer techniques to reduce the equations obtained from this analysis, and knowing the temperature at which adjacent cells die, a zone of necrosis may be mapped surrounding the acrylic impact.

ISSN:0269-3127    

DOI:10.1118/1.595902

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

Computational studies requiring the generation of pseudorandom numbers are becoming increasingly common. These include Monte Carlo methodologies and studies which require the addition of “random” noise to more structured data. Although well‐established random number generators exist, many of these are not suitable for implementation on micro‐ or minicomputer systems. An algorithm for an additive generator that can be used on any computer system is described. The performance of this algorithm as implemented on a microcomputer system is discussed. Extensive testing of the statistical behavior of the resulting number sequence was performed. The algorithm appears to be an appropriate one for a variety of applications.

ISSN:0269-3127    

DOI:10.1118/1.595903

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A theoretical analysis is made of the conventional calorimeter approach utilizing a two‐thermistor Wheatstone bridge—an approach which requires balancing the bridge by adjusting variable resistances. However, with the current availability of computers and digital precision measuring instruments, the conventional calorimeter approach can now be readily replaced by an automated, nonmechanical, electrical systems approach called differential calorimetry. The analytical theory outlining such an approach is also presented.

ISSN:0269-3127    

DOI:10.1118/1.595904

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A new method for fast magnetic resonance imaging is presented. It provides a more rapid data acquisition than two‐dimensional Fourier imaging (2DFI) by a factor which may be chosen depending on the required signal‐to‐noise ratio of the image. In addition to the readout gradient of 2DFI, the present method employs an oscillating modulation gradient. In this way, a curved alternating trajectory inkspace is sampled after each spin excitation. For ap‐times accelerated data acquisition, the trajectory consists ofpperiods, wherepis of the order of 2 to 8 for low‐frequency gradient modulation but can be chosen higher if certain hardware requirements are met. Adequate sampling density inkspace is obtained by scanning shifted trajectories after subsequent spin excitations. The method can be combined with volume imaging (3DFI) and multiple slice 2DFI. It was implemented on a standard Philips Gyroscan system without any hardware modifications. Results obtained for an acceleration factorp=4 are shown.

ISSN:0269-3127    

DOI:10.1118/1.595905

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY

摘要:

A digital radiographic system was used to measure the distribution of scattered x radiation from uniform slabs of Lucite at various thicknesses. Using collimation and air gap techniques, [primary+scatter] images and primary images were digitally acquired, and subtracted to obtain scatter images. The scatter distributions measured using small circular apertures were computer fit to an analytical function, representing the circular aperture function convolved with a modified Gaussian point spread function (PSF). On the basis of goodness of fit criterion, the proposed Gaussian function is a very good model for the scatter PSF. The measured scatter PSF's are reported for various Lucite thicknesses. Using the PSF's, the modulation transfer functions are calculated, and this spatial frequency information may have value in analytical scatter removal techniques, grid design, and air gap optimization.

ISSN:0269-3127    

DOI:10.1118/1.595906

出版商:American Association of Physicists in Medicine    

年代:1998

数据来源: WILEY