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Reducing 4DCBCT imaging time and dose: the first implementation of variable gantry speed 4DCBCT on a linear
Ricky T O'Brien1, Uros Stankovic2, Jan-Jakob Sonke2
1Radiation Physics Laboratory, Sydney Medical School, The University of Sydney, NSW 2006, Australia.
Physics in Medicine and Biology
|May 6, 2017
Summary
Respiratory Motion Guided 4D Cone Beam CT (RMG-4DCBCT) reduces imaging dose by up to 70% and improves image quality. This novel technique adapts gantry speed and imaging frequency to patient breathing for optimized CT scans.
Area of Science:
- Medical Imaging
- Radiotherapy Physics
- Image Reconstruction
Background:
- Conventional four-dimensional cone beam computed tomography (4DCBCT) utilizes constant gantry speed and imaging frequency, independent of patient respiratory rate.
- This fixed approach can lead to artifacts and suboptimal image quality due to respiratory motion.
- Previous work demonstrated dose reduction potential with respiratory motion guided 4DCBCT (RMG-4DCBCT) by adjusting imaging parameters in real-time.
Purpose of the Study:
- To implement and evaluate RMG-4DCBCT on a linear accelerator for the first time.
- To assess the impact of RMG-4DCBCT on imaging dose, imaging time, and image quality (CNR and ERW) across various respiratory rates.
- To demonstrate the ability to control image quality through real-time adjustments of gantry speed and projection acquisition.
Main Methods:
- RMG-4DCBCT was realized on an Elekta Synergy linear accelerator using a microcontroller-controlled potentiometer to adjust gantry motor speed.
- A real-time feedback loop modulated gantry speed and projection acquisition based on the patient's respiratory signal, acquiring either 40 (RMG-4DCBCT40) or 60 (RMG-4DCBCT60) projections.
- Image quality was evaluated using the CIRS dynamic Thorax phantom and patient breathing traces, measuring Contrast to Noise Ratio (CNR) and Edge Response Width (ERW).
Main Results:
- For an average patient breathing at 3.8s, imaging time and dose were reduced by 37% and 70%, respectively.
- RMG-4DCBCT40 achieved a CNR of 6.5-7.5, and RMG-4DCBCT60 achieved 8.7-9.7, demonstrating consistent and controllable CNR across respiratory rates.
- ERW in the direction of motion decreased from 2.1mm to 1.1mm with RMG-4DCBCT as breathing rate increased, contrasting with conventional 4DCBCT where ERW increased from 1.9mm to 2.5mm.
Conclusions:
- RMG-4DCBCT can be successfully implemented on a linear accelerator, enabling real-time control of image quality during 4DCBCT acquisition.
- The technique significantly reduces imaging dose and time while maintaining or improving image quality metrics like CNR and ERW.
- While RMG-4DCBCT improves image sharpness, the ERW remains dependent on the patient's breathing rate and regularity.
