Output calibration in solid water for high energy photon beams

Area of Science:

• Medical Physics
• Radiation Dosimetry

Background:

• The AAPM Protocol recommends water, polystyrene, or acrylic for high-energy photon beam output measurements.
• Conversion of dose measurements from these media to water requires specific coefficients.

Purpose of the Study:

• To investigate the accuracy of calculating restricted mass stopping powers and mass energy absorption coefficients for a water-equivalent solid.
• To validate the AAPM Protocol's methodology for determining dose to water from various measurement media.

Main Methods:

• Output measurements were performed using a Farmer type chamber.
• Measurements were conducted in four materials for Co-60 and 4-24 MV photon beams, adhering to the AAPM Protocol.
• Calculated restricted mass stopping powers and mass energy absorption coefficients were utilized.

Main Results:

• Scaled dose to water measurements across different media agreed within 1%.
• The analysis confirmed the accuracy of the published coefficients for the water-equivalent solid.
• The findings support the AAPM Protocol's approach for dose-to-water determination.

Conclusions:

• The AAPM Protocol's methodology is accurate for determining dose to water from polystyrene, acrylic, and a water-equivalent solid.
• The validated coefficients enhance the precision of radiation dosimetry in high-energy photon beams.