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.

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.

Loss of field flatness in AECL teletherapy units form misadjustment of the collimator.

Atomic Energy of Canada Limited 60Co teletherapy units have adjustable collimator hinges to adapt to source diameters from 0.75 to 2.50 cm. Adjustment of the collimator hinge to the manfacturer's settings can cause a loss of radiation field flatness as high as 20% for large fields. The recommended settings appear to clip the top corners of tall source capsules. Opening the hinge adjustment restores field flatness, without changing penumbra or the inverse square law behavior of the teletherapy unit.