SU‐E‐J‐37: The Validation Tool for Compensation of Patient Positioning Error Using DRR Images

Abstract

Purpose: The present study was designed to develop the validation tool for compensation of patient positioning error using digitally reconstructed radiograph (DRR) extracted from three‐dimensional computed tomography (3DCT) and two orthogonal kilo‐voltage x‐ray images. Methods: To generate DRR image from 3DCT, the ray casting which is most straightforward method was applied in this study. The traditional ray casting algorithm finds the intersections of a ray with all objects, voxels of the 3DCT volume in the scene, with nearest‐neighbor interpolation method. Similarity between extracted DRR and orthogonal image was measured by using normalized mutual information method. All process was done by using Matlab. Two orthogonal image was acquired from Cyber‐knife system from anterior‐posterior view and right lateral view. 3DCT and two orthogonal image of an anthropomorphic Alderson‐Rando phantom and head and neck cancer patient were applied in this study. Finally, we designed graphic user interface (GUI) for easy use. Results: Registration accuracy with average errors of 2.12 mm ± 0.5 mm for transformation and 1.23° ± 0.4° for rotation using an anthropomorphic Alderson‐Rando phantom has been acquired. Conclusion: We demonstrated that this validation tool could compensate the patient positioning error. For further study, with the developed validation GUI tool for compensation of patient positioning error, we will add the registration tool by manual/auto using cone‐beam CT and kilo‐voltage CT image to utilize clinically in heavy‐ion radiation treatment center in Korea which scheduled for completion in 2016.