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Theoretical analysis of the thread effect in helical TomoTherapy
Mingli Chen1, Yu Chen, Quan Chen
1Accuray Inc., Madison, WI, USA. mlchen@accuray.com
Medical Physics
|November 4, 2011
Summary
This study identifies factors causing the helical radiation delivery thread effect. Optimized pitch selection significantly reduces this ripple artifact, improving radiation therapy precision.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Helical radiation delivery, used in systems like TomoTherapy, can cause longitudinal dose ripples off-axis.
- This ripple artifact, known as the thread effect, is periodic and linked to pitch selection.
Purpose of the Study:
- To identify the specific factors contributing to the thread effect in helical radiation delivery.
- To analyze the impact of these factors on the thread effect and study their optimization.
Main Methods:
- Mathematical modeling of individual and combined factors (jaw profile divergence, inverse square law, attenuation, cone effect).
- Theoretical analysis and simulations to identify optimal pitches minimizing ripple amplitude.
- Verification of optimal pitches and study of optimization effectiveness.
Main Results:
- Analysis and simulations using square and real jaw profiles accurately characterized the thread effect.
- Optimal pitches showed minimal jaw width dependence, except for narrow profiles.
- Intensity modulation optimization largely suppressed the thread effect; optimal pitches varied with off-axis distance.
Conclusions:
- The proposed model effectively explains the thread effect.
- Optimization strategies can significantly reduce the thread effect.
- Predicted optimal pitches offer a valuable reference for pitch selection in radiation therapy.
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