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PubMedDate not supplied

Argon/propane ionization-chamber dosimetry for mixed x-ray/neutron fields.

The photoneutrons produced by high-energy x-ray machines can diffuse through the mazes usually employed at the treatment-room entrance and readily penetrate the lead-lined doors used for x-ray shielding. The measurement of these neutrons in the presence of x-rays and the determination of dose equivalent poses a problem for which there is currently no standard method of solution. In order to separate x-ray dose from neutron dose, the author employed an ionization chamber alternately filled with argon or propane. The response characteristics of this chamber to x-ray and neutrons are described. Quality factors were determined from a calculated neutron spectrum. As a result of these measurements, a 10-in. polyethylene door was added to the entranceway of a 25-MV linear accelerator.

Argon↗
PubMed1992

Wedge filter effects on dosimetric parameters of a linear accelerator.

The open-field and wedged-field output factors as a function of field size for two linear accelerators were measured. Wedge factors were determined by taking the ratio of the outputs with and without the wedge filter. For one linear accelerator, the difference in the output factors between the wedged field and open field can be as large as 5%. The wedge factor for this linear accelerator also varies with the field size. On the other hand, the other linear accelerator shows smaller variation of output factors between wedge field and open field. The variation of wedge factor is less than 1% for a 60 degree wedge. In addition to modifying the isodose distributions, the wedge filter also changes the percent depth dose curves, the output factor, and the wedge factor. The degree of wedge effects on these dosimetric parameters is different for different linear accelerator.

Filtration↗
PubMedDate not supplied

Measurements of backscattered radiation from Therac-20 collimator and trimmer jaws into beam monitor chamber.

The field size dependent photon output is known to be influenced by the existence of backscattered radiation (BSR) generated in the collimator or trimmer jaws of a linear accelerator. This paper describes the results of measurements made to study the existence of such backscatter by simulating the geometry of the treatment head of a Therac-20 linear accelerator. The machine's monitor chamber, flattening filter, and collimator jaws were simulated by another real monitor chamber, a 1-cm thick lead sheet and 2.5-cm thick low-melting-point alloy divergent blocks, respectively. BSR from the simulated collimator jaws (SCJ) was measured with the simulated monitor chamber (SMC) as a function of the openings of the SCJ and as a function of distance between SMC and SCJ. The present results demonstrate the presence of BSR in an 18-MV photon beam from a Therac-20 linear accelerator.

Humans↗
PubMed1983

The cost of radiotherapy treatments on a linear accelerator.

The cost of delivering a radiotherapy treatment on a linear accelerator is calculated. Items included in the cost are: cost of the accelerator itself, a simulator, a treatment planning computer, the treatment room, and the salaries of the radiographers and physicists concerned, as well as machine operating costs and interest charges. The cost of a beam direction shell is also calculated. The different costs are reduced to statements of cost per year (see Table IV for summary), and from these the cost of a course of treatment for a patient is arrived at on the basis of 800 patients treated per year. The cost comes out at pounds 137, plus pounds 70 for a beam direction shell, if one is used. Because the capital costs of radiotherapy treatment equipment are very substantial, it is often assumed that radiotherapy is a very expensive form of treatment. An analysis of treatment cost is presented, initially in terms of cost per year for equipment, special buildings, and staff at 1981 prices. Reduction of these figures to mean treatment cost per patient is based on the DHSS guideline for provision of radiotherapy services (HC(78)32), which suggests a figure of 800 patients to be treated per year as the number justifying the provision of a linear accelerator.

Costs and Cost Analysis↗
PubMed1978

Absorbed dose distributions for X-ray beams and beams of electrons from the Therac 20 Saturne linear accelerator.

After a brief description of the Therac 20 Saturne linear accelerator a complete set of absorbed-dose distribution values is given. These values define the depths on the axis as a function of the depth dose and define the penumbra (as characterized by the positions of the intersections of the isodose curves with planes parallel to the phantom surface) for beams of X-rays and for beams of electrons. Tissue-maximum ratios are given for beams of X-rays. Analytical values for the electron depth dose curve are compared with the values obtained on the Sagittaire linear accelerator.

Electrons↗
PubMed1983

Recent muon fluence measurements at Fermilab.

Muon fields at Fermilab were measured during 1980-81 using a Mobile Environmental Radiation Laboratory (MERL). During the spring of 1980, measurements were made with the accelerator operating at 350 GeV; in the spring of 1981, measurements were made at 400 GeV. The measurements were used to obtain an understanding of muon dose-equivalent rates at various locations both on and off the Fermilab site. These were found to be less than 1 mrem/yr at any given location. The data indicate that more severe problems may be encountered during operations of the 1000 GeV accelerator presently being installed.

Elementary Particles↗