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Technical note: Extension of Van Herk's treatment margin model for anisotropic systematic positioning errors in
Kiyoshi Yoda1, Keiichi Nakagawa
1Kiyoshi.Yoda@elekta.com
Medical Physics
|August 24, 2011
Summary
Treatment margins for anisotropic positioning errors were calculated using van Herk's model in a Cartesian system. These margins are smaller than isotropic models, improving patient coverage in radiation therapy.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Accurate patient positioning is crucial in radiation therapy.
- Anisotropic systematic positioning errors require specific modeling for precise treatment margins.
Purpose of the Study:
- To calculate the coefficient for a treatment margin model accounting for anisotropic systematic positioning errors.
- To apply van Herk's analytical formulation within a Cartesian coordinate system.
Main Methods:
- Formulated a three-dimensional (3D) patient population distribution in Cartesian coordinates.
- Employed analytical 3D integration with anisotropic standard deviations (Sigma) and Newton's method.
- Determined the coefficient for van Herk's systematic positioning error model.
Main Results:
- Treatment margins for anisotropic errors were 2.1 Sigma for 90% patient coverage.
- Treatment margins were 2.4 Sigma for 95% patient coverage in the Cartesian system.
Conclusions:
- Treatment margins for anisotropic systematic positioning errors in Cartesian coordinates are smaller than those for isotropic models.
- This finding suggests improved patient population coverage probability with anisotropic modeling.
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