Reduction of the Bremsstrahlung component of clinical electron beams: implications for electron arc therapy and total skin electron irradiation.

The dose due to Bremsstrahlung in stationary electron beams of nominal energies in the range 6-20 MeV is typically between 1-7% of the maximum dose and is usually not clinically significant. However, in treatments using rotational or multiple electron beams where the x-ray dose from several beams is added the x-ray dose will reach much higher proportions and will be of clinical significance. Moreover, this dose often is located in normal tissue beyond the target volume. Reduction of this x-ray dose is therefore desirable. In the present study a reduction of the x-ray component of electron beams produced by a Clinac 2100C accelerator by a change of the transmission ion chamber and scattering foils is reported. A reduction in Bremsstrahlung of up to 50% can be achieved.