Method for a motion model based automated 4D dose calculation

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• The Vero system utilizes gimbaled dynamic tumor tracking (DTT) to treat moving tumors by adjusting the radiation beam.
• Tumor motion and changing beam geometry during DTT can affect the delivered radiation dose.
• Accurate dose reconstruction is crucial for evaluating and optimizing DTT treatments.

Purpose of the Study:

• To perform a comprehensive 4D dose reconstruction for patients treated with DTT.
• To determine the necessary temporal resolution for accurate 4D dose reconstruction.
• To assess the impact of DTT on dose distribution and identify factors influencing accuracy.

Main Methods:

• Developed a 4D motion model using 4D CT data to generate pseudo-CT images for various breathing phases.
• Calculated pseudo-CT images every 100 ms and performed dose calculations based on real-time beam geometry from log files.
• Accumulated dose distributions on the planning CT and compared parameters using gamma-evaluations at different spatial-temporal resolutions.

Main Results:

• Accumulated 4D dose distributions showed a mean Gross Tumor Volume (GTV) dose reduction of 0.77% compared to static plans.
• Observed larger dose deviations in some patients, particularly with lower 4D CT quality.
• Gamma-evaluation indicated that a temporal resolution of 500 ms is sufficient for accurate dose reconstruction.

Conclusions:

• A temporal resolution of 500 ms is adequate for precise 4D dose reconstruction in DTT treatments.
• Considering tumor motion with a spatial-temporal sampling of 1400 ms and 2 mm provides accurate results while reducing workload by 84%.
• Optimizing temporal and spatial resolution is key to balancing accuracy and efficiency in DTT-based radiotherapy.