[unreadable] Radiation therapy remains to be one of the most important procedures for treating cancer. The goal of conformal radiation therapy is to deliver a high radiation dose to the target volume that contains the cancerous tissue, while minimizing the radiation exposure of healthy tissues that surround this volume. When delivering the treatment, it is critically important that the position and orientation of the patient (or more specifically, the tumor volume and radiation sensitive structures that surround it) are consistent with those assumed when designing the treatment plan. if there are errors in the positioning of the patient, the effectiveness of the treatment may be degraded and a large radiation dose may be delivered to healthy tissues surrounding the target volume. The broad objective of this proposal is to develop and investigate dose-efficient tomographic image guided treatment methods that will provide a clinically-viable solution for detecting patient positioning errors in conformal radiation therapy treatments. Unlike previously proposed tomographic approaches, our methods will be based on the theory of local tomography, and consequently will only utilize megavoltage X-ray radiation that passes through or very near the tumor volume to form the reconstructed image of the tumor volume. The specific aims of the proposed research are: (1) To develop and investigate local tomography algorithms for reconstructing two-dimensional 2D) images of a tumor volume, (2) To develop and investigate local tomography algorithms for reconstructing three-dimensional(3D) images of a tumor volume, (3) To investigate the feasibility of reconstructing 2D and 3D images of a tumor volume using truncated projections that correspond to treatment beam orientations, and (4) To quantitatively and objectively evaluate the ability of the algorithms to reconstruct accurate and clinically useful tumor volume images. The successful completion of our proposed work could provide a clinically viable solution to the patient positioning problem and could improve the accuracy of the delivery of radiation therapy treatment procedures. By increasing the conformality of the radiation therapy treatment procedure, the chances of survival for cancer patients could be improved while simultaneously minimizing the risk of radiation-induced complications. [unreadable] [unreadable]