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PubMed2002

Measurements of effective doses of natural background level of neutrons with etched-track detectors.

An etched-track method was applied for a measurement of the effective dose of natural background neutrons. Ten assemblies of polycarbonate film and 10B were placed at the center of a rem-counter type moderator. The assemblies were put in an air-tight container in order to avoid a continuous contribution from radon. Electrochemical etching was adopted. The sensitivity of the detector was 0.21 +/- 0.02 microSv pit(-1) cm2. After a period of storage of 4.3 y, the number of recorded artifact pits in the films corresponded to an effective dose rate of 0.8 +/- 0.2 microSv y(-1). The effective dose rate of natural background neutrons was 18.1 +/- 3.6 microSv year(-1) for the same period, with an artifact dose being subtracted. The total net number of etched-track pits of the present detector was 75 +/- 15 when used for measuring an effective dose of natural background level neutrons for 1 mo, which gives enough counting statistics. The method can thus be applied for monitoring the effective dose of neutrons around nuclear sites and high-energy accelerator facilities.

Calibration↗
PubMed2002

A personal-computer-based method to obtain "star-shots" of mechanical and optical isocenters for gantry rotation of linear accelerators.

This work describes a method to obtain "star-shots" of the mechanical and optical isocenters of linear accelerators, similar to the star-shots of radiation isocenters normally obtained using films. In this method a digital camera is connected to a personal computer so that multiply exposed images can be taken at a fixed camera position. A mechanical pointer or a wire aligned along the optical axis can then be imaged by the camera. Multiple exposures at varying gantry angles are then superimposed on a digital image which can be analyzed by the computer to give a high-resolution star-shot. The method provides a convenient way for a linear accelerator quality assurance procedure.

Computer Simulation↗
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↗
PubMed2003

[Determination of head scatter factors released from a scanning-type therapeutic accelerator].

The MM50 is a racetrack microtron capable of taking out photon beams and electron beams with energies of up to 50 MeV. It flattens the beam by the beam-scanning method, while the microtron MM22 utilizes a flattening filter. The head-scatter factors (hereafter called S(h)), which are important for evaluating the output of the photon beam of the MM50 and MM22, were measured using a mini-phantom and build-up cap. S(h) measured with the build-up cap showed the influence of contaminated electrons, whereas S(h) measured with the mini-phantom showed less influence, even for 50 MV photon beams. Compared with the MM22, the MM50 showed less change in S(h) according to field size and energy. The reason for this seemed to be that the MM50 has a smaller extra-focal region than other accelerators equipped with flattening filters and, therefore, can essentially be considered a point source by using the beam-scanning method without a flattening filter. This study demonstrated that photons scattered by the flattening filter used for beam flattening in typical medical accelerators mainly contribute to S(h).

Filtration↗
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↗
PubMed2002

Relativistic E x B acceleration.

The relativistic motion of charged particles is analyzed theoretically in electric and magnetic fields that are constant, uniform, and mutually perpendicular. In the relativistic regime where the magnitude of the electric field E is equal to or greater than that of the magnetic field B, i.e., |E| > or =|B|, the particle is effectively accelerated and gains energy indefinitely. This is quite different from the E x B drift motion in the nonrelativistic regime.

Journal Article↗