Beam quality, surface doses, depths of maximum dose, peak dose rates, beam profiles, and central axis percentage depth doses of a medical microtron's 21 MV photon beam were measured. The half-value layer of lead was 1.35 cm, the half-value layer of water was 23 cm, and the nominal acceleration potential was 17.7 MV. For a 10 X 10 cm2 field at 100 cm SSD, the maximum dose occurred at a depth of 3 g X cm-2 and the surface dose was 18% of the maximum. The highest dose rate at isocenter was approximately 800 cGy X min-1. The worst horns on beam profiles occurred at a depth of 5 cm for the 35 X 35 cm2 field where the dose rate 4 cm from the edge of the beam was 3% higher than that on the central ray. No horns were apparent for fields 25 X 25 cm2 or smaller.
Humans Radiotherapy, High-Energy