Determination of MLC model parameters for Monaco using commercial diode arrays

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• Accurate characterization of multileaf collimators (MLCs) is crucial for precise intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT).
• The Monaco X-ray voxel Monte Carlo (XVMC) algorithm requires optimized MLC parameters for reliable dose calculations in treatment planning systems.

Purpose of the Study:

• To evaluate the suitability of MapCHECK 2 and ArcCHECK diode arrays for optimizing MLC parameters within the Monaco XVMC algorithm.
• To compare the performance of MapCHECK 2 and ArcCHECK in measuring dose distributions for MLC-modulated beams.

Main Methods:

• Radiation test beams were delivered to MapCHECK 2, ArcCHECK, and EBT3 Gafchromic film for comparative analysis.
• MLC parameters in the XVMC algorithm were initially optimized using MapCHECK 2 measurements, with Gafchromic film used for verification.
• Gamma analysis (3% and 2 mm criteria) was employed to assess the agreement between calculated and measured dose distributions.

Main Results:

• Optimization of XVMC MLC parameters using MapCHECK 2 significantly improved agreement with calculated doses, with the lowest gamma pass rate increasing from 68.5% to 93.5%.
• ArcCHECK measurements showed discrepancies, particularly overestimating dose for rectangular fields aligned with its long axis, leading to lower gamma pass rates (70.0%-97.9%).
• Gafchromic film confirmed the accuracy of MapCHECK 2 measurements, supporting its use in the optimization process.

Conclusions:

• MapCHECK 2 is a more suitable detector than ArcCHECK for optimizing MLC parameters in the Monaco XVMC algorithm due to its superior accuracy and reliability.
• ArcCHECK exhibited measurement issues that led to significant discrepancies in dose distribution evaluations for specific beam configurations.
• The optimized MLC model, validated by MapCHECK 2 and film, serves as a benchmark for assessing detector performance in IMRT/VMAT quality assurance.