Experimental verification of a Monte Carlo-based MLC simulation model for IMRT dose calculation

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Accurate dose calculation in intensity modulated radiation therapy (IMRT) is essential for effective cancer treatment.
• Inter- and intra-leaf transmission and head scatter significantly impact IMRT dose delivery.
• Precise modeling of the multi-leaf collimator (MLC) and accelerator treatment head components is critical for accurate IMRT planning.

Purpose of the Study:

• To develop and validate a comprehensive Monte Carlo (MC) model of the Varian 120 leaf MLC.
• To assess the accuracy of the developed MLC model in simulating various IMRT delivery scenarios.
• To compare MC calculations with experimental measurements for static and dynamic IMRT fields.

Main Methods:

• Utilized the DPM MC code with a custom geometry module to simulate the Varian 120 leaf MLC and collimating jaws.
• Performed verification tests including leakage, leaf positioning, and static MLC shapes.
• Calculated and compared doses for clinical IMRT plans (breast, prostate, head and neck) against film measurements.

Main Results:

• The MC model demonstrated agreement within 2% for static MLC shapes compared to film and ion-chamber measurements.
• Overall agreement for clinical IMRT plans was within 2% /2 mm of film data.
• The head and neck split field showed discrepancies up to 5% in high dose regions.

Conclusions:

• The developed comprehensive MC model of the Varian 120 leaf MLC accurately simulates IMRT dose deliveries.
• The model is validated for various IMRT beam configurations, demonstrating its utility in treatment planning.
• Further investigation into discrepancies for complex fields like head and neck split fields is warranted.