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The first implementation of respiratory triggered 4DCBCT on a linear accelerator
Ricky T O'Brien1, Benjamin J Cooper, Chun-Chien Shieh
1Radiation Physics Laboratory, Sydney Medical School, The University of Sydney, NSW 2006, Australia.
Physics in Medicine and Biology
|April 8, 2016
Summary
Respiratory Triggered 4DCBCT (RT-4DCBCT) reduces radiation dose in radiotherapy imaging by suppressing redundant projections. This technique significantly lowers imaging dose while maintaining image quality, improving patient safety during treatment.
Area of Science:
- Medical Physics
- Radiotherapy Imaging
- Image Guidance
Background:
- Conventional four-dimensional cone beam computed tomography (4DCBCT) uses constant gantry speed and projection rates, leading to unnecessary radiation exposure due to redundant data acquisition.
- Theoretical studies suggest that suppressing these redundant projections can reduce imaging dose by 40-50% with minimal impact on image quality.
Purpose of the Study:
- To experimentally validate a projection suppression technique, termed Respiratory Triggered 4DCBCT (RT-4DCBCT), for reducing imaging dose in radiotherapy.
- To assess the impact of RT-4DCBCT on image quality and intra-phase bin displacement variations.
Main Methods:
- Developed a real-time control system for RT-4DCBCT, using respiratory signals to trigger or suppress projection acquisition.
- Utilized a CIRS dynamic thorax phantom with simulated breathing periods (2-8 seconds) and assessed image quality via edge response width, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR).
- Evaluated intra-phase bin displacement variations using the standard deviation of a 3 cm imaging insert in the superior-inferior direction.
Main Results:
- RT-4DCBCT achieved dose reductions of 8.6% to 77% for breathing periods from 2 to 8 seconds compared to conventional 4DCBCT.
- Intra-phase bin displacement variation was reduced by 13-43%, indicating more consistent projection positioning within respiratory phases.
- For a 4-second breathing period, edge response width improved by 39% with only a 6-7% decrease in SNR and CNR.
Conclusions:
- RT-4DCBCT has been successfully implemented and demonstrated to significantly reduce imaging dose during radiotherapy.
- The experimental results confirm that RT-4DCBCT maintains diagnostic image quality while improving the consistency of image acquisition relative to patient motion.
