Proton dosimetry comparison involving ionometry and calorimetry

Area of Science:

• Medical Physics
• Radiation Dosimetry
• Particle Therapy

Background:

• Accurate absorbed dose determination is critical for effective proton therapy.
• Intercomparison studies are essential to ensure consistency in dosimetry protocols across different centers.

Purpose of the Study:

• To compare absorbed dose measurements using ionization chambers and a calorimeter in a 200 MeV proton beam.
• To evaluate the impact of different stopping power data and dosimetry protocols on measurement agreement.

Main Methods:

• Four European proton therapy centers participated in the study.
• Measurements were performed using various ionization chambers and an A-150 plastic calorimeter.
• Absorbed dose calculations were based on different codes of practice, including Janni's tables and ICRU Report no. 49.

Main Results:

• Ionization chamber measurements of absorbed dose to A-150 plastic agreed within 1%.
• The calorimeter to chamber dose ratio improved from 0.952 (using Janni's tables) to 0.985 (using ICRU Report no. 49 data).
• Using the AAPM protocol with new stopping power tables yielded a ratio of 1.002, indicating excellent agreement.

Conclusions:

• Updated proton stopping power data significantly improves agreement between calorimeter and ionization chamber dosimetry.
• The study highlights the importance of standardized protocols and up-to-date data for accurate proton therapy dosimetry.
• Faraday cup measurements showed good charge agreement but significant dose underestimation, indicating sensitivity to experimental conditions.