Monte Carlo simulation-based patient-specific QA using machine log files for line-scanning proton radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Science

Background:

• Quality assurance (QA) is critical for safe and accurate pencil-beam proton therapy.
• Conventional patient-specific QA (pQA) is limited and labor-intensive, necessitating improved methods.
• Ensuring treatment plan integrity is paramount in advanced proton therapy techniques.

Purpose of the Study:

• To develop and verify a Monte Carlo (MC) simulation-based QA method for line-scanning proton therapy.
• To assess machine performance and its impact on patient treatment accuracy.
• To reflect uncertainties in scanning beam delivery within the QA process.

Main Methods:

• Utilized the Tool for Particle Simulation (TOPAS) for nozzle modeling and commissioned against measurements.
• Acquired beam delivery uncertainty data from log files recorded during patient plan delivery.
• Performed MC simulations in a solid water phantom for 68 clinical cases, comparing 2D dose distributions with ionization chamber array measurements.
• Employed gamma analysis with 3%/3 mm and 2%/2 mm criteria to compare simulated and measured dose distributions.

Main Results:

• Achieved high absolute gamma passing rates (e.g., 96.76% for 2%/2 mm criterion against measurements).
• Demonstrated low standard deviations in passing rates, indicating method consistency (e.g., 3.99% SD for 2%/2 mm criterion).
• Evaluated false-positive and false-negative rates, showing reduction with a 90% passing rate threshold.

Conclusions:

• Successfully developed a log-file-based MC simulation method for patient-specific QA in line-scanning proton therapy.
• The method demonstrated clinically acceptable accuracy, validating its potential.
• Proposed as a replacement for measurement-based dosimetry QA with a 90% gamma passing rate threshold using the 2%/2 mm criterion.