The Key Technique Research Of Image Guided Radiotherapy On Cone Beam Computed Tomography

Tumor radiation therapy has entered into a new era, in which tumor is being treated by 3-dimentional conformal radiotherapy (3D-CRT) and intensity modulated radiotherapy (IMRT). A typical representative of the new treatment technology is the image guided radiotherapy (IGRT) based on the cone-beam computed tomography (CBCT), with which there's a great improvement on the accuracy and precision of treatment.One of the key issues in IGRT clinical application is achieving accurate and rapid registration for Planning CT and CBCT. Existing registration methods cannot still satisfy the clinical implementation requirements in the speed and accuracy. In this paper, mutual information based multi-resolution registration framework is used to accelerate the registration process. Theoretically and experimentally, it's demonstrated that multi-scale space based multi-resolution three-dimensional medical image registration framework can greatly increase the speed of registration process rather to direct registration. We realized that mutual information based rigid registration algorithm for IGRT system by registering CBCT of the three-dimensional image reconstruction of patients with the Planning CT of the patient treatment model. Furthermore, two multi-resolution registration frameworks are compared: direct equidistant sampling pyramid and Gaussian pyramid. Studies have shown that direct equidistant sampling pyramid framework can be implemented quickly to complete registration, and with better robustness; and moreover mutual information-based registration method can be used to overcome the limitation of the current bone-shaped characteristics based framework for the registration. Now we can get high precision and robustness, and there is no need to extract features and easy to achieve automatic registration etc. It is very suitable for CBCT and Planning CT registration for image guided radiation therapy.Another key issue is the evaluation standard and quality control system on CBCT. The dissertation studied on and developed innovatively an evaluation standard and quality control system, which are based on the image uniformity, image resolution, CT value stability, space linearity, and dose on the isocenter. With them, it is more feasible and easy to design and evaluate a radiotherapy plan based on CBCT.A 2D kinetic phantom system, which is used to simulate respiratory motion, has been developed to study on the impacts of organs motion and deformation upon CBCT. From tests, it has been revealed that the impacts of respiratory motion upon the reconstruction and deformation of CBCT images in latitude and longitude directions were remarkable. Compared to the CBCT images under quiescence, it was fuzzy and deformed, with a larger volume. Respiratory extent played an important role in it, but the frequency not.The dissertation has studied and developed a new program to paste two respective CBCT images to enlarge length of CBCT images, and offer the integrity of structures. The process is that importing two CBCT image series to TPS and then fusion the planning CT and CBCT together. Find the same layer of two CBCT series by analyzing the two fusion results and the bone as the reference. When enlarged, more information including tumor and organs at risk (OAR) could be integrated. This new technique can provide the chance to observe the whole target and OAR and the chance for physicists to evaluating the treatment plan and re-planning based on CBCT.