Advanced tracking and image registration techniques for intraoperative radiation therapy

Resumen

Intraoperative electron radiation therapy (IOERT) is the delivery of radiation to the surgically opened tumor bed without irradiating healthy tissue. Treatment planning systems and mobile linear accelerators enable clinicians to optimize the procedure, minimize the stress in the operating room (OR) and avoid transferring the patient to a dedicated radiation room. However, radiation collimator placement over the tumor bed requires a validation methodology to ensure the correct delivery of the prescribed dose distribution previously planned in the TPS. In this dissertation, we address three well known IOERT limitations: applicator positioning over the tumor bed, docking of the mobile linear accelerator gantry with the applicator and validation of the prescribed dose delivery. This thesis demonstrates that these limitations can be overcome by providing the actual applicator position with respect to the patient’s anatomy. The main objective of this work is to assess technological and procedural alternatives to improve the IOERT performance and solve the described uncertainty problems. In particular, image-to-world registration, multicamera optical trackers, multimodal imaging techniques and the mobile linear accelerator docking are revisited in the IOERT context. IOERT is carried out by a multidisciplinary team in a highly complex environment that has special tracking needs due to its working volume characteristics ―large and prone-to-occlusions- in addition to the accuracy requisites. The first part of this dissertation presents the validation of a commercial multicamera optical tracker in terms of accuracy, sensitivity to miscalibration, camera occlusions and detection of tools using a feasible surgical setup; and proposes an automatic miscalibration detection protocol that satisfies the IOERT requirements of automaticity and speed. We show that the chosen multicamera tracker is suitable for IOERT navigation and demonstrate the feasibility of the miscalibration detection protocol in clinical setups. Image-to-world registration is one of the main issues during image-guided applications where the field of interest and/or the number of possible anatomical localizations is large, such as IOERT. In the second part of this dissertation a registration algorithm (LBR) for image-guided surgery based on line-shaped fiducials is proposed and validated. LBR decreases the acquisition time during surgery and improves the registration accuracy in comparison to available algorithms in the literature. In the third part of this dissertation, we integrate a commercial low-cost ultrasound transducer, a cone beam CT C-arm and an optical tracker for image-guided interventions that enables surgical navigation and explores image-based registration techniques for both modalities. In the fourth part of this dissertation a navigation system based on optical tracking for the docking of the mobile linear accelerator to the radiation applicator is assessed, improving safety and reducing the procedure time. The system tracks the prescribed collimator localization to solve the movements that the linear accelerator should perform to reach the docking position and warns the user about potentially unreachable arrangements before the actual procedure. A software application was implemented to use this system in the OR, where it was also evaluated to assess the improvement in docking speed. Finally, in the las part of this dissertation, we present and assess the installation setup of a navigation system in a dedicated IOERT OR, determine the required steps in the IOERT process, identify the workflow limitations and evaluate the feasibility of the integration of the system in a real OR. The navigation system safeguards the sterile conditions of the OR, clears the space for surgical operation and is suitable for any similar dedicated IOERT OR.