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At least 127 records · Page 7Linked to original sources
PubMedDate not supplied

Bremsstrahlung review: an analysis of the Schiff spectrum.

A concise approximate formula computed by Schiff for the intensity spectrum of bremsstrahlung photons has been a valuable starting point for many medical physics applications, including the Task Group 21 protocols. This paper provides a brief review of the literature related to determination of the bremsstrahlung spectrum and to the Schiff formula in particular. It describes the approximations Schiff made to obtain this formula, including the Born approximation, and the exponential nuclear screening potential, the infinite-mass nucleus approximation, and the "extreme relativistic" approximation. A derivation of a more exact formula that avoids the last of these approximations is presented. This provides a check on the accuracy of the Schiff spectrum for linear accelerator energies used clinically. Comparisons with the Schiff thin-target result are presented. A thick-target bremsstrahlung spectrum is calculated and compared with the forward spectrum obtained from Monte Carlo simulations of the x-ray production in two linear accelerator treatment heads.

Particle Accelerators↗
PubMed1980

A simple electron cone interlock system for the clinac-18.

A simple electron cone-collimator interlock system has been developed for the Clinac-18. Each cone is assigned a special slot in the storage cabinet and, upon being taken for treatment setup, sends out a binary coded decimal (BCD) signal to the control console. The voltage from the collimator setting must match the BCD signal or a comparator logic will drive the fault matrix to prevent the accelerator from energizing.

Electrons↗
PubMed1983

[Tissue activation by bremsstrahlung from medical accelerators].

If a continuous radiation with a maximum energy of more than 10.55 MeV is used in radiotherapy, there is an activation of tissue. A radiation exposure of the staff may be connected with this activity induced by the nuclear photon effect. The consequences for routine radiotherapy are demonstrated by the examples of a betatron 42 MeV and a linear accelerator Clinac 20.

Humans↗
PubMed1992

Asymmetric field calculations.

A simple method for performing manual dose calculations in asymmetric fields is proposed. The method is based on a generalized central-axis dose calculation equation for which open- and wedged-field off-axis provisions have been made. A calculation form designed to document the calculation and simplify the calculation process is presented. Lastly, the required off-axis dosimetry data obtained from a dual-energy accelerator are shown.

Humans↗
PubMed1983

Electron depth-dose dependence on energy spectral quality.

Electron depth-dose curves and spectra have been measured from an experimental accelerator on which both energy and spectral shape could be varied independently. The measurements were made at nominal energies of 6 and 12 MeV, with the energy spread (FWHM) varied from 1.7% to over 10% of average energy. Changes in depth-dose fall-off characteristics correlated only weakly with the width of the accelerator's spectrum. The use of a single accelerator and experiment set-up eliminated the differences that have complicated previous comparisons of beams of different spectral quality, which have been based upon data from different accelerator designs.

Particle Accelerators↗
PubMedDate not supplied

Off-axis beam quality change in linear accelerator x-ray beams.

The effective energy of the x-ray beam from linear accelerators changes as a function of the position in the beam due to nonuniform filtration by the flattening filter. In this work, the transmittance through a water column was measured in good geometry and the beam quality characterized in units of HVL in water. Measurements were made on a variety of linear accelerators from 4 to 10 MV. The beam energy decreased with increasing distance from the central ray for all accelerators measured.

Particle Accelerators↗
PubMedDate not supplied

Electron beam simulation applicators.

A system for simulating electron beam treatment portals using low-temperature melting point alloy is described. Special frames having the same physical dimensions as the electron beam applicators used on the Varian Clinac 20 linear accelerator were designed and constructed.

Electrons↗
PubMedDate not supplied

Determination of the source position for the electron beams from a high-energy linear accelerator.

We have investigated the energy and field-size dependence of the source position of the electron beams from a Varian Clinac-2,500 accelerator. Three independent experimental methods were used: (1) multipinhole camera (MPC), (2) back projection of the full width at half maximum (FWHM), and (3) the inverse square law (ISL). The positions of the virtual and effective sources were calculated using the multiple Coulomb scattering (MCS) formalism. The results obtained from the MPC agree, within the experimental uncertainties, with the calculated values for the virtual source position. Similarly, the results from the FWHM method agree with the calculations with the exception of those for small field sizes at the lower energies. This is consistent with the fact that both kinds of measurements are not very sensitive to scattering in the photon and electron collimators. In contrast, the source position determined by the ISL method shows strong dependence on field size and energy, and does not agree with the values predicted by the MCS formalism. This is due to contamination from electrons scattered in the x ray and electron collimation system. The techniques and results reported here should be generally applicable to other scatter foil linear accelerators.

Electrons↗
PubMed1988

[Radioactivity in dismantling a betatron].

The authors report on the specific radioactivity of construction components of a 42 MeV betatron measured 28 days after the last run by means of a Ge spectrometer (ultra-pure germanium detector employed in a semiconductor spectroscopic method) recording the gamma spectra of various components of the betatron. This examination served to find out which components would have to be considered as radioactive waste requiring special treatment in accordance with Federal German legislation on radioactive waste disposal (section 47 of the Radiation Protection Ordinance). The examination showed that such special treatment would be required only for the target (main material: platinum) and the Platness-filter (chief constituent: lead) of the decommissioned electron accelerator.

Humans↗