Multi-angle beam range measurement framework for carbon-ion radiotherapy using a commercial multi-layer ionization...

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Radiation Detection and Measurement

Background:

• Accurate beam range verification is crucial in carbon-ion radiotherapy due to unique physical challenges.
• Conventional water phantom methods are time-consuming for routine quality assurance (QA).

Purpose of the Study:

• To develop and validate an efficient framework for carbon-ion beam range verification using a multi-layer ionization chamber (MLIC).
• To significantly reduce the time required for comprehensive QA measurements.

Main Methods:

• Utilized a commercial MLIC with a beam-model-based fitting method and reference integral depth-dose curves.
• Implemented a time-optimized, trigger-free acquisition process and a gantry-compatible mount for multi-angle measurements.
• Evaluated measurement uncertainty via range-shift experiments and clinical feasibility through stability and consistency tests.

Main Results:

• Achieved low range-determination uncertainty (0.24 mm, k=3) with excellent agreement to water phantom measurements (0.03 ± 0.15 mm).
• Reduced measurement time for all energy levels from over 50 hours to approximately 15 minutes (>100-fold improvement).
• Demonstrated high stability (long-term 0.17 mm, multi-angle 0.05 mm, k=1) and identified machine inconsistencies missed by conventional QA.

Conclusions:

• The proposed MLIC-based framework offers a reliable, accurate, and highly efficient solution for routine beam range QA in carbon-ion therapy.
• The framework is feasible for frequent, comprehensive verification across all energy levels and gantry angles, enhancing patient safety.