Optimizing the MLC model parameters for IMRT in the RayStation treatment planning system

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Treatment Planning

Background:

• Commercial treatment planning systems (TPS) model multi-leaf collimator (MLC) rounded leaf ends variably.
• RayStation TPS uniquely employs a step function for MLC transmission through rounded leaf ends.

Purpose of the Study:

• To optimize and validate the MLC model parameters within the RayStation TPS.
• To ensure accurate dose calculations for Intensity-Modulated Radiation Therapy (IMRT).

Main Methods:

• Iterative optimization of MLC parameters (leaf-tip offset, width, transmission factor, tongue-and-groove) in RayStation v. 4.0.
• Validation using measured data from a Varian C-series linac and IMRT QA plans.
• Comparison with AAPM Task Group 119 report data and independent measurements.

Main Results:

• Optimized MLC parameters for 6 MV and 18 MV photons: leaf-tip offset = 0.3 cm, transmission = 2.5%, tongue-and-groove width = 0.05 cm.
• High passing rates (>97.5% for 6 MV, >90.9% for 18 MV at 2 mm/2% gamma analysis) for TG-119 IMRT QA cases.
• Favorable agreement between computed and measured output factors for small fields.

Conclusions:

• The optimized MLC model parameters in RayStation TPS provide accurate dose calculations for IMRT.
• The validated parameters serve as a valuable reference for other users of the RayStation system.
• This work enhances the reliability of radiation therapy planning and delivery.