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What is the optimum leaf width of a multileaf collimator?
1Deutsches Krebsforschungszentrum, Department of Medical Physics, Heidelberg, Germany. T.Bortfeld@dkfz-Heidelberg.de
Medical Physics
|December 29, 2000
Summary
The optimal leaf width for a multileaf collimator is determined by sampling theory, with the sampling distance being more critical than leaf width. Leaf width can be up to twice the sampling distance without significant physical degradation in dose distribution.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Physics
Background:
- Dose distributions in radiotherapy are inherently smooth due to radiation-matter interactions.
- Sampling theory can represent dose distributions using discrete samples.
- The distance between samples relates to multileaf collimator leaf centers.
Purpose of the Study:
- To determine the optimal leaf width for multileaf collimators (MLCs) to avoid diminishing physical improvements in dose distribution.
- To investigate the relationship between MLC leaf width and sampling distance.
Main Methods:
- Applied sampling theory and linear systems theory to analyze dose distribution.
- Approximated the dose deposition kernel using a Gaussian function.
- Derived optimum sampling distance from the 20%-80% penumbra width.
Main Results:
- The optimum sampling distance is approximately 1.5-2 mm for a 6 MV beam, calculated as the 20%-80% penumbra divided by 1.7.
- In the regular case, the optimum leaf width equals the sampling distance.
- Leaf widths up to twice the sampling distance result in minor dose distribution deterioration, correctable by deconvolution.
Conclusions:
- Sampling distance is a more critical parameter than leaf width for MLCs.
- MLC leaf width can be up to twice the sampling distance.
- The derived sampling distance is valuable for optimizing fluence and dose grids in treatment planning algorithms.