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A three-source model for the calculation of head scatter factors
Yong Yang1, Lei Xing, Arthur L Boyer
1Department of Radiation Oncology, Stanford University, California 94305-5304, USA. yong@reyes.stanford.edu
Medical Physics
|September 28, 2002
Summary
This study presents a new algorithm for calculating the head scatter factor (Sc) in radiation therapy. The method accurately predicts Sc for irregular fields, crucial for intensity modulated radiation therapy, with results closely matching measurements.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Dosimetry
Background:
- Accurate head scatter factor (Sc) determination is critical in intensity modulated radiation therapy (IMRT).
- Irregular field shapes in IMRT, often smaller than collimator settings, pose challenges for traditional Sc calculations.
Purpose of the Study:
- To develop and validate a novel algorithm for calculating the head scatter factor (Sc).
- To accurately determine Sc for symmetric, asymmetric, and irregular open fields generated by tertiary collimators.
Main Methods:
- An algorithm based on a three-source model was developed, considering primary and two extra-focal photon sources.
- The Kim et al. field mapping method was extended to incorporate scatter contributions from multiple source planes.
- The algorithm was implemented in C/C++ and validated against experimental measurements for various field configurations.
Main Results:
- The developed algorithm demonstrated high accuracy, with most calculated Sc values agreeing with measurements within 0.4%.
- The method effectively handles irregular fields shaped by multileaf collimators (MLCs).
Conclusions:
- The proposed three-source model algorithm provides accurate head scatter factor calculations for diverse field shapes in radiation therapy.
- This algorithm is a valuable tool for improving dose accuracy in IMRT, particularly for complex and irregular fields.