Photon contamination in 8-20-MeV electron beams from a linear accelerator

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Electron beams in radiation therapy can carry photon contamination.
• Conventional methods may underestimate the dose contribution of this contamination to superficial tissues.

Purpose of the Study:

• To directly measure X-ray contamination near the surface of a phantom irradiated with electron beams.
• To determine if photon contamination contributes a higher superficial dose than conventionally indicated.

Main Methods:

• Used a magnetic field to deflect electron beams from a linear accelerator.
• Studied electron energies ranging from 8 to 20 MeV.
• Measured photon contamination characteristics directly in a water tank.

Main Results:

• Significant photon contamination was detected in all tested electron beam energies.
• Measured photon contamination qualities matched theoretical bremsstrahlung spectra.
• This suggests a potential for increased superficial dose not accounted for by standard dosimetry.

Conclusions:

• Direct measurement confirms substantial X-ray contamination in clinical electron beams.
• This contamination may lead to an overestimation of superficial dose in radiation therapy.
• Findings necessitate re-evaluation of dosimetry protocols for electron beam treatments.