Interference of 433 MHz microwaves with a megavoltage linear accelerator

Most radiotherapy departments currently applying local hypothermia use radiofrequency or microwave equipment, frequently in rooms within a short distance of linear accelerators. In this study, it has been shown that microwave intensities of about 0.4 mW cm-2 in the control room of the Sagittaire accelerator can interfere with the functioning of the accelerator and result in a higher beam energy. Increases in beam energy of up to 14% were measured. This was the results of direct interference with the beam bending system. However, the increase in beam bending current indirectly influences the acceleration of the electrons (and thus the electron energy) via feedback circuits for gun-emission and RF-power. No significant influence of microwaves upon the dosimetry system of this accelerator was found. (U.K.)