AbstractID: 7894 Title: Image-Guided Radiation Therapy with FOCAL (Fusion Of CT And Linac): Comparison with Treatment Verification by Bony Landmarks A first-of-its-kind CT scanner has been installed in the linac room (Primatom) at Morristown Memorial Hospital. Since June 2000, we have been providing prostate, lung and liver cancer patients with FOCAL (Fusion Of CT And Linac) radiation treatment. This paper describes our image registration method for FOCAL irradiation, and compares the accuracy of FOCAL vs. conventional treatment verification by bony landmarks. For image registration, we print out beforehand the beam’s eye view (BEV) of the treatment fields. Prostate tumor volume from each Primatom CT slice is mapped on the printouts, and the necessary isocenter shift is deduced. The accuracy of the Primatom system and this image registration has been thoroughly checked. No port film is necessary for our Primatom patients. We generate digitally-reconstructed radiographs (DRRs) with bone contrast from the CT scans, and deduce the required shifts as the difference between the DRRs of the Primatom CT vs. the planning CT. For 10 patients we found that shift obtained from bony landmark significantly correlated with the Primatom CT shift. Positioning adjustment based on bony anatomy is generally in the right direction. However, adjustments with bony landmarks frequently do not go far enough, and substantial positional differences exist between treatment guided by Primatom CT vs. bony images. Our study confirms that prostate organ motion relative to the bones has an average discrepancy of 4.7 mm, and shows the superiority of FOCAL treatment guided by Primatom CT vs. conventional bony structure (such as port film) verification. Primatom is a product of Siemens Medical Systems.