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SU-E-T-88: Evaluating Gantry Sag on Linear Accelerators and Introducing an MLC-Based Compensation Strategy
Medical Physics
|May 19, 2017
Summary
Gantry sag, a mechanical error in radiation therapy, can be accurately measured and reduced. A new strategy using the multi-leaf collimator (MLC) effectively compensates for gantry sag, improving dose delivery accuracy.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Equipment
Background:
- Gantry sag is a known mechanical imperfection affecting radiation therapy's spatial accuracy.
- Quantifying and compensating for gantry sag is crucial for precise radiation dose delivery.
Purpose of the Study:
- To quantify gantry sag across multiple linear accelerators (linacs).
- To investigate a multi-leaf collimator (MLC)-based strategy for gantry sag compensation.
Main Methods:
- Winston-Lutz method used to measure gantry sag on three Varian linacs.
- Ball-bearing phantom imaged during gantry rotation to derive radiation isocenter and gantry sag.
- MLC leaf positions offset at 90-degree collimator angle for compensation.
Main Results:
- Gantry sag was reproducible, varying from 0.7 mm to 1.0 mm across linacs.
- Inferior movement of the radiation field center observed during gantry rotation.
- MLC compensation reduced maximum gantry sag to < 0.2 mm.
Conclusions:
- Gantry sag can be precisely measured using a ball-bearing phantom and electronic portal imaging.
- Gantry angle-specific MLC corrections effectively reduce gantry sag.
Keywords:
CollimatorsImage analysisImage guided radiation therapyLinear acceleratorsMultileaf collimatorsMore Related Videos
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