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A stochastic convolution/superposition method with isocenter sampling to evaluate intrafraction motion effects in
Shahid A Naqvi1, Warren D D'Souza
1Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA. snaqvi@umm.edu
Medical Physics
|May 18, 2005
Summary
This study introduces a novel, faster method for calculating radiation dose distributions during organ motion, improving accuracy and accounting for specific machine effects. The new approach accurately predicts dose variations, aiding clinical decisions on treatment margins.
Area of Science:
- Medical Physics
- Radiation Oncology
- Computational Biology
Background:
- Current dose calculation methods for organ motion (dose convolution, fluence convolution) have limitations, including artifacts and shift-invariance assumptions.
- Accurate dose calculation is crucial for effective intensity-modulated radiation therapy (IMRT) and managing motion-induced uncertainties.
Purpose of the Study:
- To develop and validate a novel, accurate, general, and fast algorithm for calculating dose distributions with organ motion.
- To investigate the impact of patient-specific motion on dose distribution and inform clinical decisions regarding treatment margins.
Main Methods:
- A new algorithm samples isocenter points from patient-specific motion trajectories and simulates photon transport through a 3-D collimator and phantom.
- The method explicitly models Machine-specific effects (MLC, scatter, spectral hardening) and accounts for changes in source-surface distance.
- Continuous sampling avoids motion discretization, enabling calculations as fast as static dose computations.
Main Results:
- The novel method demonstrated agreement within 2 mm for isodose curves compared to film measurements for a 2 cm motion amplitude.
- Interfraction dose variability due to interplay effects averages out over typical multifraction treatments.
- Simulations revealed motion-induced asymmetric penumbral spreading, suggesting direction-specific margin adjustments.
Conclusions:
- The developed method offers improved accuracy, generality, and speed for dose calculation with organ motion.
- The findings support the use of patient-specific motion data to guide treatment planning, optimize margins, and potentially escalate doses.
- This computational approach can be performed quickly, aiding real-time clinical decision-making.