摘要:

The effects caused by bone present in phantoms irradiated by negatively charged pions on absorbed dose, cell survival, oxygen enhancement ratio, and relative biological effectiveness have been estimated using Monte Carlo methods. The influence of bone along the pion path and also the influence of a bone–tissue interface parallel to the direction of motion of the pions have been considered. Calculated results, as a function of spatial coordinates in a 30‐g/cm2‐thick tissue phantom with bone both included and excluded, are presented. All of the biological data reported here are for T‐1 human kidney cells. The extent to which the effects of bone in the path of the pion beam can be approximated by using results for tissue and measuring depth in the phantom in g/cm2is considered and discussed.

ISSN:0269-3127    

DOI:10.1118/1.1637312

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

The results from the literature on acoustics in suspensions, excluding the phenomena of relaxation, have been applied to study the effects of red‐cell and plasma densities, compressibilities, viscosities, thermal conductivities, and surface tension on the propagation of sound in blood. For the calculations of the viscous and the thermal absorptions and of the velocity of sound in blood, the red cell may be treated as a rigid spherical particle containing the same volume. For the calculation of the thermal absorption, the erythrocyte may be treated as a spherical particle of finite thermal conductivity at all frequencies; but for the calculation of the velocity of sound, the effect of heat conduction can be ignored above 1 MHz and Wood's sound velocity formula may be used. The calculated sound absorption due to shear viscosity and thermal conduction in whole blood constitutes a significant portion (about 60% or more) of the measured value of the total absorption toward the lower‐frequency range (1 MHz or less) and a negligible portion (about 15% or less) of the total absorption toward the higher‐frequency range (10 MHz or more).

ISSN:0269-3127    

DOI:10.1118/1.1637313

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

Fast neutron beams produced by 17.3‐MeV deuterons incident on a totally stopping beryllium target, a totally stopping deuterium gas target, and a 5.8‐MeV‐thick deuterium‐gas target are compared. It is shown that the deuterium‐gas target yields a significantly higher average energy and dose rate and may offer other advantages as well.

ISSN:0269-3127    

DOI:10.1118/1.1637314

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

Cobalt‐60 teletherapy dose calculations utilizing a standard correction factor for thorax inhomogeneities can result in dose error due to patient variability. Individual intracavitary measurements avoid this error but are impractical for routine clinical use. A graph has been constructed relating the ratio of measurements made with and without the patient in the beam to an equivalent water depth. With an ordinary ion chamber secured to the beamstopper, the dose was integrated during a 1‐min rotation. A known water depth was used to derive apparent linear attenuation coefficients which, with the equationD0 / Dt = eμt, enabled construction of the graph. To verify the method, tubes with dosimeters were positioned at the axis of rotation during the first treatment of patients with esophageal tumors. Agreement of corrected dose with measured dose is within 3% for 360 deg rotational treatment; uncorrected dose calculations would have resulted in errors of 5%–21%.

ISSN:0269-3127    

DOI:10.1118/1.1637315

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

Radioactive potassium‐38 has been produced by the photonuclear reactions39K(γ,n)38Kand40Ca(γ,n p)38K, using the bremsstrahlung field developed by an electron linear accelerator. Non‐carrier‐free38K was produced by irradiating potassium hydroxide pellets for 30 min using 10 kW of 40 MeV electrons passing through a thick tantalum converter. Yields of 25–35 mCi38K per gram irradiated KOH were obtained. Carrier‐free38K was produced by similarly irradiating shredded calcium metal, obtaining 2–6 mCi per gram of calcium. In both cases, the target material was dissolved in HCl, neutralized, and prepared as sterile solutions of KCl for injection.

ISSN:0269-3127    

DOI:10.1118/1.1637316

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

摘要:

The addition of a current limiting resistor to the high‐voltage polarizing batteries of an ionization chamber is described to reduce accidental shock to personnel and possible equipment damage.

ISSN:0269-3127    

DOI:10.1118/1.1637317

出版商:American Association of Physicists in Medicine    

年代:2003

数据来源: WILEY

ISSN:0269-3127    

DOI:10.1002/j.2473-4209.1974.tb36052.x

出版商:Wiley    

年代:2003

数据来源: WILEY