Variation in output with a fixed dose setting on a 4-MV linear accelerator.

Abstract

Variations in the output with a fixed monitor unit setting as a function of magnetron power of a 4-MV linear accelerator has been studied. The relationship between radiation output and monitor units was found to vary by as much as 10%. The central-axis depth dose was found to remain constant within experimental error. Field flatness measurements indicated that for lower power outputs, the radiation field was less flat than for higher power outputs. A mechanism for the change in calibration is suggested based upon field flatness measurements.