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A method for determining multileaf collimator transmission and scatter for dynamic intensity modulated radiotherapy
M R Arnfield1, J V Siebers, J O Kim
1Department of Radiation Oncology, Medical College of Virginia at Virginia Commonwealth University and McGuire VA Hospital, Richmond 23298, USA. marnfield@hsc.vcu.edu
Medical Physics
|December 1, 2000
Summary
This study presents a practical method for measuring multileaf collimator (MLC) transmission and scatter, crucial for dynamic intensity-modulated radiotherapy. Accurate MLC data ensures precise radiation delivery in cancer treatment.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Physics
Background:
- Accurate characterization of multileaf collimator (MLC) performance is essential for commissioning dynamic intensity-modulated radiotherapy (IMRT).
- The sweeping window technique in IMRT requires precise MLC leaf trajectory data derived from transmission and scatter properties.
Purpose of the Study:
- To demonstrate a practical method for determining MLC leaf transmission and scatter characteristics.
- To provide essential data for converting IMRT optimization system intensity distributions into dynamic MLC leaf trajectories.
Main Methods:
- Film-based measurements of MLC leakage for various field sizes on Varian 2100C and 2100EX accelerators.
- Analytical calculations of direct transmission, considering detailed leaf geometry and Monte Carlo-generated energy spectra.
- Monte Carlo simulations to calculate dose to phantom beyond a closed MLC.
Main Results:
- Measured MLC leakage was 1.68% for a 10x10 cm2 field at 6 and 18 MV for the 80-leaf MLC.
- Leakage comprised 1.48% direct transmission and 0.20% leaf scatter at 6 MV.
- Analytical and Monte Carlo results for direct transmission and phantom dose showed excellent agreement; dynamic sweeping window calculations agreed with measurements within 2%.
Conclusions:
- A practical method for MLC transmission and scatter characterization is demonstrated.
- Measured transmission is crucial as it depends on MLC alloy density, necessitating individual MLC measurements.
- The findings support accurate MLC leaf control for dynamic IMRT delivery.
