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Study of the IMRT interplay effect using a 4DCT Monte Carlo dose calculation.
Michael D Jensen1, Ady Abdellatif, Jeff Chen
1Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada. mjensen4@uwo.ca
Physics in Medicine and Biology
|April 4, 2012
Summary
Respiratory motion causes radiotherapy dose errors. A new simulation method using log files and 4D CT accurately models these interplay effects, showing gating reduces errors.
Area of Science:
- Medical Physics
- Radiotherapy
- Computational Biology
Background:
- Respiratory motion during radiotherapy can cause significant dose errors, particularly with complex intensity-modulated radiation therapy (IMRT) techniques.
- The interplay between dynamic multileaf collimator (MLC) motion and patient breathing can lead to unpredictable dose distributions.
Purpose of the Study:
- To develop and validate a novel treatment reconstruction simulation code that accurately accounts for interplay effects in intensity-modulated radiation therapy (IMRT) delivery under respiratory motion.
- To evaluate the sensitivity of different IMRT plan types to interplay effects and assess the efficacy of gating in mitigating these effects.
Main Methods:
- A treatment reconstruction simulation code was developed, integrating MLC controller logs, respiratory trace logs, 4D CT images, and a Monte Carlo dose calculator.
- Experiments were conducted using two 3D IMRT step-and-shoot plans (concave target and integrated boost) delivered to a 1D rigid motion phantom under varying duty cycle gating conditions (100%, 50%, 25%).
- Multiple simulation types (continuous isocenter shift, discrete isocenter shift, 4DCT, 4DCT delivery average, 4DCT plan average) were performed and analyzed using 3D gamma analysis (2%/2 mm criteria).
Main Results:
- The simulation framework successfully demonstrated that an integrated boost plan is more susceptible to interplay effects compared to a concave target plan.
- Gating strategies were shown to be effective in reducing the impact of interplay effects during radiotherapy delivery.
- The developed 4D CT Monte Carlo simulation method, utilizing delivery log files, accurately accounts for IMRT interplay effects caused by respiratory motion.
Conclusions:
- A validated 4D CT Monte Carlo simulation approach effectively models IMRT interplay effects with respiratory motion using delivery log files.
- Understanding and mitigating interplay effects through techniques like gating is crucial for accurate dose delivery in thoracic and abdominal radiotherapy.
- The developed simulation tool provides a valuable method for predicting and analyzing dose errors in motion-managed radiotherapy.
