On-line Image Guided Radiation Therapy using Cone-Beam CT (CBCT)

Purpose: Using cone beam CT, we can compare the position of the patients at the simulation and the treatment. In on-line image guided radiation therapy, one can utilize this compared data and correct the patient position before treatments. Using cone beam CT, we investigated the errors induced by setting up the patients when use only the markings on the patients' skin. Materials and Methods: We obtained the data of three patients that received radiation therapy at the Department of Radiation Oncology in Chung-Ang University during August 2006 and October 2006. Just as normal radiation therapy, patients were aligned on the treatment couch after the simulation and treatment planning. Patients were aligned with lasers according to the marking on the skin that were marked at the simulation time and then cone beam CTs were obtained. Cone beam CTs were fused and compared with simulation CTs and the displacement vectors were calculated. Treatment couches were adjusted according to the displacement vector before treatments. After the treatment, positions were verified with kV X-ray (OBI system). Resutts: In the case of head and neck patients, the average sizes of the setup error vectors, given by the cone beam CT, were 0.19 cm for the patient A and 0.18 cm for the patient B. The standard deviations were 0.15 cm and 0.21 cm, each. On the other hand, |n the case of the pelvis patient, the average and the standard deviation were 0.37 cm and 0.1 cm. Conclusion: Through the on-line IGRT using cone beam CT, we could correct the setup errors that could occur in the conventional radiotherapy. The importance of the an-line IGRT should be emphasized in the case of 3D conformal therapy and intensity-modulated radiotherapy, which have complex target shapes and steep dose gradients.