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UBC Theses and Dissertations

3D ultrasound-based patient positioning for radiotherapy Wang, Michael Haizhou

Abstract

A novel 3D ultrasound-based patient positioning system for target localisation during radiotherapy is described. This system incorporates the use of optically tracked dedicated 3D ultrasound probes to acquire images of the target anatomy during both the radiotherapy simulation and treatment procedures. The ultrasound scan taken during simulation is registered to the planning CT so that the prescribed dose plan can be transferred to the simulation ultrasound coordinates. Finally, this ultrasound is registered to the treatment ultrasound image using a rigid-body intensity-based registration algorithm to localise the target at the time of treatment. This thesis first describes the method for registering CT and 3D ultrasound scans taken during the radiotherapy simulation procedure using infra-red LED (IRED) markers of the optical position sensing system directly as fiducial markers in CT. This approach was tested on a phantom and a RMS target registration error (TRE) of 1.09mm was achieved. In addition, an automatic intensity-based registration algorithm was shown to be capable of registering 3D ultrasound images acquired from the neck of a volunteer. Finally, a novel experimental technique is described which allows the entire radiotherapy treatment process using the proposed 3D ultrasound-based patient positioning system to be simulated. This method uses polymer gel dosimetry to record the dose delivered to a phantom, allowing this to be compared to the intended dose plan, thereby closing the loop on the entire treatment process. The mean target localisation accuracy of the proposed system was 2.5mm for 4 target locations inside the phantom, compared to 1.6mm obtained using the conventional patient positioning method of alignment lasers. These results suggest that 3D ultrasound-based target localisation is practically feasible and and potentially capable of increasing the accuracy of patient positioning for radiotherapy treatment in sites where day-to-day organ shifts are greater than 1mm in magnitude.

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