UBC Theses and Dissertations
Rigid registration of 3D ultrasound images and computed tomography images for permanent breast seed implant brachytherapy treatment planning Zhang, Xiaoying
Purpose: The purpose of this work is to further develop and to validate a prototype three-dimensional ultrasound (3DUS) system for permanent breast seed implant (PBSI) planning procedure. PBSI is a novel brachytherapy technique for early-stage breast cancer patients. Palladium-103 seeds are planned around the seroma cavity and implanted through the guidance of a needle implant template. Currently, PBSI plans are made based on computed tomography (CT) images, while the delivery is guided under freehand 2D ultrasound (US) images in the operating room. The difference on seroma visualization on CT and US complicates the interpretation of the plan during the delivery. A prototype PBSI 3DUS system has been developed and 3DUS images are desired for improved visualization in PBSI treatment planning. Materials and Methods: The PBSI 3DUS system includes a motorized scanner that drives a 2D US probe during scanning. An encoded mechanical arm is mounted on the scanner and tracks the location of the needle implant template, and the template can be then registered into the 3DUS imaging volume for visual guidance. A method was developed to rigidly register 3DUS images with CT images through a point-based registration. A 3D-printed model was made to provide visible landmarks in both imaging volumes. Gel breast phantoms were constructed to test the registration feasibility and accuracy. Results: A 3D-printed model with eight landmarks ranging over 6 cm in three dimensions was adopted for 3DUS-CT rigid registration process. The registration was performed on gel breast phantoms, with the 3DUS scanner oriented in a 40 range of lateral orientation. The average registration error was (1.9 ± 0.8) mm. The maximum error in 25 3DUS-CT registration trials was 4.6 mm, and 19 out of 25 (76%) trials had a registration error less than 2 mm. Conclusions: This work facilitated the clinical implementation of the PBSI 3DUS system. The 3DUS system was commissioned and a clinical quality assurance (QA) procedure with baseline data was made to monitor the system performance. A method was developed to achieve 3DUS-CT rigid registration and the registration was tested on gel breast phantoms.
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