Water calorimeter dosimetry for 160 MeV protons

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Proton Therapy

Background:

• Accurate absorbed dose determination is critical for effective proton beam therapy.
• Water calorimeters offer a direct method for measuring absorbed dose, independent of radiation-dependent parameters.
• Ionization chambers, calibrated using established protocols like AAPM Report 16, are widely used but require validation for proton beams.

Purpose of the Study:

• To compare absorbed dose measurements from a water calorimeter with those from ionization chambers for a 160 MeV proton beam.
• To assess the reliability of the water calorimeter as an absorbed dose standard.
• To validate the use of AAPM Report 16-compliant ionization chambers for proton beam dosimetry.

Main Methods:

• A flexible, temperature-regulated, sealed glass core water calorimeter was employed.
• Absorbed dose to water was measured using the water calorimeter.
• Measurements were compared against ionization chambers calibrated according to AAPM Report 16.

Main Results:

• Two independent experiments yielded dose ratios of 0.992 +/- 0.004 and 0.990 +/- 0.004 between the water calorimeter and ionization chambers.
• The close agreement between the two methods indicates consistent absorbed dose determination.
• The absence of radiation-dependent parameters in the calorimeter's operation enhances its reliability.

Conclusions:

• The water calorimeter demonstrates high reliability as an absorbed dose standard for proton beams.
• The findings support the continued use of 60Co-calibrated ionization chambers, following AAPM Report 16, for proton beam dosimetry.
• This study contributes to the evidence base for advanced dosimetry techniques in proton therapy.