An improved technique for aligning the light field with the radiation fields on radiotherapy accelerators.

An improved scheme has been developed for measuring the coincidence of the light field and radiation fields of a radiotherapy accelerator. Scans of the light and radiation fields are made sequentially using a photodiode on standard field plotting apparatus. By superimposing the two plots, differences between the two fields' boundaries can be accurately determined. The technique is simple and avoids uncertainties inherent in common techniques employing film.

Using ion chambers with wedge-shaped absorbers for electron energy measurements.

A parallel-plate ionization chamber placed behind a wedge-shaped absorber and exposed to a radiotherapeutic electron beam exhibits an energy-dependent response. Such a device designed to produce a linear energy dependence has been built and tested. The device yields results during exposure, and the difficulties of film handling, associated with similar procedures, have been eliminated. The precision of the device makes it suitable for use as a routine means of monitoring energy for quality assurance purposes.

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.

Dosimetry measurements of 26, 35 and 45 MeV p-Be and p-Li neutron beams.

Dosimetric properties of neutron beams produced by stopping 26, 35 and 45 MeV protons in beryllium and lithium have been measured. The effects of filtering the p-Be beam with 6 cm of polyethylene have been investigated. The tissue kerma rate in air exhibited an energy dependence of approximately E3 and the rate for p-Be beams was approximately one-fifth of the rate for d-Be beams. The penetrability of the neutrons was significnatly enhanced by the use of the filter, but with a 50% attentuation in tissue kerma rate. The tissue kerma rate for the p-Li beam was nearly the same as that for the p-Be beam.

Physical characterization of neutron beams produced by protons and deuterons of various energies bombarding beryllium and lithium targets of several thicknesses.

Protons of 35 and 65 MeV and deuterons of 35 MeV were used to bombard beryllium and lithium targets of various thicknesses. Four types of experiments were conducted in order to characterize the neutron fields. They were (1) central axis depth-dose measurements in a water phantom, (2) dose buildup at small depths in tissue-equivalent plastic, (3) microdosimetric measurements and LET distributions, and (4) neutron yields and energy spectra at an angle of 0 deg. The results generally show that (a) the central axis depth doses for the 35 and 65 MeV particles roughly approximate those of 60Co and 4-MeV bremsstrahlung photons, respectively, (B) the neutron dose buildups are more rapid than those of the above-mentioned photon sources, (C) the microdosimetric spectra show differences which are consistent with the measured neutron energy spectra, and (D) P-Li compared to p-Be neutron spectra have larger high-energy particle flux for similar target and beam configurations.

Neutron energy spectra and dose-distribution spectra of cyclotron-produced neutron beams.

Neutron energy spectra and spectra of dose deposition in tissue-equivalent material have been measured for neutron sources produced by 16-, 22-, 35-, and 45.5-MeV deuterons and 22.5-, 35-, 45-, and 65.5-MeV protons incident upon a thick beryllium target. Neutron spectra were measured using time-of-flight techniques and the dose distribution was measured using a 1/2 in. spherical "tissue-equivalent" proportional counter filled with "tissue-equivalent" gas.

Proton-beryllium neutron production at 25-55 MeV.

The production of neutrons by stopping 25-, 35-, 45-, and 55-MeV protons in beryllium has been studied. The yield of neutrons in the forward direction can be approximated by the relation: yield = -0.032X10(16).E+0.0027X10(16).E2 neutrons/C sr. The neutron spectra are characterized by a low-energy evaporation component which has small angular dependence and a high-energy component which is peaked in the forward direction. Neutrons produced in the forward direction have an average energy approximately 40% of the incident proton energy.