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Biomedical subjects

R F Moyer

Publications and source records attributed to R F Moyer.

7 recordsLinked to original sources
PubMed1983

A surface bolus material for high-energy photon and electron therapy.

The authors describe a useful bolus material for therapy with high-energy photons and electrons (greater than 1 MeV). Qualities evaluated included flexibility, transparency, tissue equivalence (re radiation interactions), stability at high doses, durability, lack of toxicity, ease in cleaning, low flammability, and cost. Using a parallel-plate ionization chamber and 60Co, 4-, and 10-MV photons as well as 6- and 18-MeV electrons, maximum deviation from water-equivalent values was approximately 2 mm for 6-MeV electrons. The material comes in large sheets of precise thickness (+/- 0.5 mm) which can be cut and layered to form more complex shapes.

Elastomers↗
PubMed1981

Quality assurance of electron-beam energy using an aluminum wedge.

An aluminum wedge was designed to facilitate evaluation of the constancy of high-energy electron teletherapy beams (6-18 MeV). Ready-packed film was exposed with the wedge on top, and optical density distribution was recorded with a scanning densitometer. Energy-dependent statistics were obtained using the practical-range extrapolation method. The procedure takes approximately 15 minutes and requires less than one minute of therapy machine time. Repeated daily measurements on a medical linear accelerator at 12 MeV showed a variation of +/- 0.37 MeV (3 sigma). This technique has proved useful for prompt machine evaluation following malfunctions and has been incorporated into routine quality assurance testing.

Aluminum↗
PubMed1978

Systematic patient-dose errors for 4- and 10-MeV microwave linear accelerators associated with rectangular collimator settings.

Systematic patient-dose errors relating to standard equivalent-square approximations and movable collimator-exchange effect were evaluated for rectangular fields of photon beams from 4- and 10-MeV microwave electron accelerators (Varian Clinac 4 and Clinac 18). Errors approached 2.5% at nominal treatment depths for highly elongated rectangular fields. The collimator-exchange effect should be considered when (a) evaluating ionization-chamber stem effect, (b) specifying relative output factors for rectangular fields, and (c) evaluating equivalent-square-field algorithms.

Humans↗
PubMedDate not supplied

Lead as surface bolus for high-energy photon and electron therapy.

Dose distributions were evaluated under thin sheet lead used as surface bolus for 4- and 10-MV photons and 6- and 9-MeV electrons using a parallel-plate ion chamber and film. A narrow, significantly low dose region (-17%) was noted for 4-MV photons, whereas a 6% increase in dose was present for 10-MV photons. The dose was elevated 15%-22% near the surface of electron fields with lead bolus, but depth dose relationships were similar to soft-tissue-equivalent (STE) bolus. Investigation of partial-field bolus (2-cm-diam circle) documented reduced doses due to lack of lateral electron equilibrium for 10-MV photons, which was less evident using lead, and large edge effects (up to 30%) for electrons using either lead or STE bolus. Dose distributions on sloped surfaces with electron fields were similar for lead and STE; both require thickness adjustment to achieve a desired effective thickness normal to the surface. Lead bolus has been used successfully in clinical practice for photons.

Electrons↗
PubMedDate not supplied

The mysterious wall around exposure.

The quantity, exposure, and its associated unit, the roentgen, have been employed for approximately 50 years for the practical measurement of x- and gamma-ray source "output." Practical exposure-measuring devices must be provided with a wall of critical thickness and composition. Confusion arises since the wall is not mentioned in the definition of "exposure." This mystery can be dispelled by the fact that exposure never is measured in the manner in which it is defined.

Cobalt Radioisotopes↗