Dual ring multilayer ionization chamber and theory-based correction technique for scanning proton therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Particle Therapy

Background:

• Accurate depth dose measurements are crucial for effective pencil beam scanning proton therapy.
• Existing methods can be time-consuming and may exhibit discrepancies with water phantom measurements.

Purpose of the Study:

• To develop a multilayer ionization chamber (MLIC) and a correction technique for fast and accurate depth dose measurements in proton therapy.
• To minimize differences between MLIC and water phantom measurements.

Main Methods:

• Developed a dual ring multilayer ionization chamber (DRMLIC) capable of independent electron collection for Percentage Depth Dose (PDD) and Integrated Depth Dose (IDD) measurements.
• Implemented a semi-empirical correction model, tuned with water phantom measurements, to account for nuclear interaction cross-section differences.
• Applied a correction factor dependent on incident energy to raw DRMLIC data before integration.

Main Results:

• DRMLIC measurements, using the correction technique, showed good agreement with water phantom data for IDDs and PDDs across various energies (71.6-221.4 MeV).
• Gamma index analysis (1%/1 mm) showed high agreement, with >94.5% of points passing for IDDs and 97% for PDDs.
• Range differences in the water phantom were less than ±0.3 mm, indicating high spatial accuracy.

Conclusions:

• The developed correction technique effectively suppresses discrepancies between MLIC and water phantom depth dose profiles.
• The DRMLIC enables rapid measurement of both IDD and PDD, proving useful for quality assurance in proton therapy.
• The combination of the DRMLIC and correction technique offers a valuable tool for precise depth dose profiling in pencil beam scanning proton therapy.