External beam irradiation angle measurement using a hybrid Cerenkov-scintillation detector

Area of Science:

• Medical Physics
• Radiation Detection
• Radiotherapy Technology

Background:

• Accurate measurement of external beam irradiation angles is crucial for radiotherapy quality assurance.
• Existing methods may have limitations in direct angle measurement.
• Cerenkov light's angular dependency offers a potential avenue for novel detection methods.

Purpose of the Study:

• To develop and validate a novel Cerenkov probe for direct measurement of external beam irradiation angles.
• To investigate the influence of electron energy spectrum on Cerenkov emission.
• To assess the detector's accuracy and potential for radiotherapy quality assurance.

Main Methods:

• A Cerenkov probe utilizing a filtered PMMA optical fiber was constructed.
• Simultaneous dose measurements were performed using a plastic scintillation detector.
• Angular calibration curves were generated using electron and photon beams.
• The impact of numerical aperture on angular dependency was analyzed.

Main Results:

• The Cerenkov probe demonstrated accurate irradiation angle measurements with low mean errors (e.g., 1.02° at 18 MV).
• Beam energy significantly impacted angular calibration curves due to Cerenkov emission cone properties.
• Reducing numerical aperture improved angular dependency at lower energies.
• The detector showed promising accuracy across various electron and photon beam energies.

Conclusions:

• The developed Cerenkov probe provides a direct and accurate method for measuring external beam irradiation angles.
• The detector's performance is influenced by beam energy and probe design parameters.
• This technology holds significant potential for quality assurance in advanced radiotherapy techniques like SRS and MRgRT.