Independent Monte-Carlo dose calculation for MLC based CyberKnife radiotherapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Biology

Background:

• Accurate dose calculation is crucial for patient-specific quality assurance (QA) in radiation therapy.
• CyberKnife systems utilize multi-leaf collimators (MLCs) requiring precise QA methods.
• Independent dose calculation (IDC) provides an essential verification step for treatment plans.

Purpose of the Study:

• To develop, implement, and validate a Monte Carlo (MC)-based IDC framework.
• To enable patient-specific QA for MLC-based CyberKnife treatment plans.
• To compare MC-based IDC results with treatment planning system (TPS) calculations and experimental measurements.

Main Methods:

• Utilized an MC beam model with phase spaces and EGS++ library for MLC transport.
• Employed DOSXYZnrc for dose scoring, processing XML treatment plans and DICOM CT data.
• Validated the framework using single beam profiles in a water tank and a prostate plan with Gafchromic film measurements.

Main Results:

• IDC dose profiles agreed within 2.3% or 1 mm of water tank measurements.
• 99.9% of voxels passed gamma analysis comparing film measurements to IDC calculations.
• 99.0% of voxels passed gamma analysis comparing IDC to TPS calculations for a clinical prostate plan.
• IDC dose was up to 5.6% lower than TPS dose near metal fiducial markers.

Conclusions:

• Successfully developed and validated a modular, MC-based IDC framework for CyberKnife QA.
• The framework is ready for patient-specific QA, enhancing treatment plan verification.
• Demonstrated the framework's accuracy against measurements and TPS calculations, highlighting its clinical utility.