Real-time prostate trajectory estimation with a single imager in arc radiotherapy: a simulation study.

Area of Science:

• Medical Physics
• Radiotherapy Technology
• Image-Guided Therapy

Background:

• Accurate real-time prostate tracking is crucial for effective intensity-modulated arc radiotherapy.
• Modern linear accelerators often feature a single gantry-mounted X-ray imager suitable for intrafraction imaging.
• Existing methods may require specialized equipment or multiple imaging devices.

Purpose of the Study:

• To develop and validate a method for real-time 3D prostate position estimation using a single X-ray imager during arc radiotherapy.
• To quantify the accuracy of this estimation method in simulated treatment scenarios.
• To assess the impact of imaging frequency and pre-treatment imaging duration on accuracy.

Main Methods:

• Simulated projection of prostate marker trajectories onto a single rotating X-ray imager.
• Utilized Gaussian probability density functions (PDFs) estimated via maximum likelihood optimization.
• Incorporated pre-treatment imaging sequences for initial PDF estimation.
• Quantified accuracy using root-mean-square (RMS) estimation error.

Main Results:

• Achieved a mean 3D RMS estimation error of 0.22 mm under optimal conditions (1 min treatment, 5 Hz imaging, 20s pre-treatment).
• Errors exceeding 1 mm occurred in only 0.8% of cases for 1 min treatments.
• Accuracy showed slight degradation with reduced imaging frequency or pre-treatment duration.
• Mean errors increased to 0.27 mm and 0.30 mm for 2 and 3 min treatments, respectively.

Conclusions:

• The developed single-imager method enables accurate real-time 3D prostate tracking during arc radiotherapy.
• This approach leverages standard equipment on modern linear accelerators.
• The findings support the implementation of image-guided real-time prostate tracking using existing technology.