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A fast jaw-tracking model for VMAT and IMRT Monte Carlo simulations
Reid Townson1, Hilary Egglestone2,3, Sergei Zavgorodni3
1Measurement Science and Standards, National Research Council Canada, Ottawa, ON, Canada.
Journal of Applied Clinical Medical Physics
|May 11, 2018
Summary
This study introduces an efficient Flat-Absorbing-Jaw-Tracking (FAJT) model for Monte Carlo (MC) dose calculations in radiotherapy. The FAJT model significantly speeds up simulations for jaw-tracking techniques while maintaining high accuracy for dose verification.
Area of Science:
- Medical Physics
- Radiotherapy Physics
- Computational Dosimetry
Background:
- Modern radiotherapy, including Volumetric Arc Therapy (VMAT) and Intensity Modulated Radiotherapy (IMRT) with jaw-tracking, necessitates accurate dose calculations.
- Monte Carlo (MC) methods offer high accuracy for radiotherapy dose calculations but can be computationally intensive.
- Dynamic motion of secondary collimators (jaws) coupled with multi-leaf collimators (MLCs) in jaw-tracking requires efficient modeling.
Purpose of the Study:
- To present an efficiency-enhancement method for secondary collimator modeling in MC-based dose second checks.
- To introduce the Flat-Absorbing-Jaw-Tracking (FAJT) model for improved computational speed in radiotherapy dose calculations.
- To evaluate the accuracy and efficiency of the FAJT model in comparison to full MC simulations and clinical dose reconstruction methods.
Main Methods:
- Developed the Flat-Absorbing-Jaw-Tracking (FAJT) model, simplifying secondary collimator modeling by neglecting transmission and scatter, and treating jaws as perfectly absorbing planes.
- Integrated the FAJT model into the VCU-MLC model to couple jaw and MLC motion for jaw-tracking simulations.
- Performed Gamma-index analysis comparing FAJT dose distributions with full BEAMnrc MC simulations and evaluated against EPIDose and Eclipse AAA for clinical cases.
Main Results:
- FAJT achieved over 99% pass rate (2%/2 mm criteria above 10%) against full BEAMnrc MC simulations for various field types and treatment plans.
- Simulation speed for secondary collimators increased by factors of 237, 1489, and 1395 for 4x4, 10x10, and 30x30 cm2 open fields, respectively.
- Clinical simulation times were reduced from hours to minutes, with average 2%/2 mm gamma-test success rates of 96.8% (vs. EPIDose) and 97.3% (vs. Eclipse AAA) above the 80% isodose.
Conclusions:
- The FAJT model provides a significant efficiency enhancement for MC-based secondary collimator modeling in radiotherapy.
- This method maintains MC transport advantages in patient heterogeneities while drastically reducing computation time.
- FAJT is a viable and accurate tool for MC-based dose second checks and treatment planning, enabling faster and reliable dose verification.
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