Validation of a prototype DiodeAir for small field dosimetry

Area of Science:

• Medical Physics
• Radiation Detection and Measurement

Background:

• Standard diode detectors exhibit over-response in small radiation fields due to silicon's high mass-density.
• Monte Carlo simulations suggest mass-density compensation, like incorporating an air-gap, can optimize dosimeter performance.

Purpose of the Study:

• To determine the ideal air-gap thickness for a PTW 60017 unshielded diode detector using Monte Carlo simulations.
• To experimentally validate the performance of a modified diode detector with an integrated air-gap in small radiation fields.

Main Methods:

• Utilized egs_chamber Monte Carlo simulations to predict optimal air-gap thickness.
• Developed and tested prototype diode detectors with varying air-gap thicknesses.
• Conducted experimental validation using a 6 MV linear accelerator and EBT3 film for comparison.

Main Results:

• A 1 mm air-gap in the PTW 60017 diode (DiodeAir) resulted in on-axis correction factors near unity for a 10x10 cm² field.
• Lateral performance, including Full Width at Half Maximum (FWHM) and penumbra, was consistent with EBT3 film measurements.
• The DiodeAir's performance in Percentage Depth Dose (PDD) measurements matched the original diode, and simulations showed robustness up to 15 MV.

Conclusions:

• Mass-density compensation via an air-gap is an effective strategy to improve diode detector accuracy in small radiation fields.
• The DiodeAir prototype demonstrates reliable performance across various field sizes and beam energies.
• Further application of this method to other detectors like diamond detectors could enhance small-field dosimetry.