A practical Monte Carlo MU verification tool for IMRT quality assurance

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Quality assurance (QA) for intensity-modulated radiation therapy (IMRT) is crucial but time-consuming with traditional methods like ionization chambers and film dosimetry.
• The Monte Carlo (MC) method offers high accuracy for radiotherapy dose calculations but suffers from slow computation speeds.
• Developing efficient MC tools is essential for practical application in clinical settings.

Purpose of the Study:

• To develop a fast Monte Carlo monitor unit (MU) verification tool for IMRT, making MC calculations practical for clinical QA.
• To improve the efficiency of MC dose calculations for IMRT treatment planning and beam delivery verification.
• To validate a novel point detector method for rapid and accurate dose estimation.

Main Methods:

• Utilized a "point detector" estimator employing the next event estimation (NEE) method for photon energy fluence calculation.
• Converted photon energy fluence to collision kerma, assuming transient charged particle equilibrium.
• Reconstructed actual MLC leaf sequences from dynamic leaf-sequence log files for patient dose prediction.

Main Results:

• The developed MU verification tool demonstrated a 20-fold speedup compared to direct MC simulations (EGS4/MCSIM).
• Calculations using the point detector method agreed within 2% with direct MC simulations for 20 patient plans.
• The tool was validated against phantom measurements and is suitable for both patient dose verification and phantom QA.

Conclusions:

• The fast Monte Carlo MU verification tool, utilizing the point detector method, offers a practical and efficient solution for IMRT QA.
• This method significantly reduces QA time while maintaining high accuracy, comparable to established MC codes.
• The tool enables accurate patient dose verification and phantom QA, enhancing the safety and efficiency of IMRT delivery.