An analytical approach for optimizing the leaf design of a multi-leaf collimator in a linear accelerator

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Equipment

Background:

• Multi-leaf collimators (MLCs) are crucial for shaping radiation beams in linear accelerators.
• Vendor-specific MLC designs involve trade-offs between performance parameters like resolution and field size.
• Optimizing MLC leaf geometry is essential for precise dose delivery in cancer treatment.

Purpose of the Study:

• To develop an analytical approach for optimizing the leaf design of a multi-leaf collimator (MLC).
• To characterize and quantify the impact of design compromises on MLC performance.
• To determine an optimal leaf design for a six-bank MLC balancing high-resolution field shaping and large field size.

Main Methods:

• A linear accelerator model was created, incorporating parameters such as source size, maximum field size, and source-to-isocenter distance.
• An analytical model was used to calculate geometric, transmission, and total penumbra widths (80-20%) based on leaf design parameters.
• The model was validated against existing collimator designs from major vendors (Elekta, Varian, Siemens).

Main Results:

• The optimal leaf tip radius was determined by minimizing penumbra width and ensuring its constancy during leaf movement.
• Transmission penumbra width dominates for leaves thinner than 4 cm, while geometric penumbra is significant for leaves near the source.
• An optimal six-bank MLC leaf design was achieved using specific leaf thicknesses (3.5 cm, 4 cm, 5 cm) for different banks.

Conclusions:

• The developed analytical model accurately predicts MLC performance and aids in optimizing leaf design.
• The optimized MLC design offers enhanced field-shaping capabilities for improved radiotherapy precision.
• This approach provides a framework for designing advanced MLCs tailored to specific clinical requirements.