Multimodality image registration quality assurance for conformal three-dimensional treatment planning

Purpose: We present a quality assurance methodology to determine the accura cy of multimodality image registration and fusion for the purpose of confor mal three-dimensional and intensity-modulated radiation therapy treatment p lanning. Registration and fusion accuracy between any combination of comput ed tomography (CT), magnetic resonance (MR), and positron emission computed tomography (PET) imaging studies can be evaluated. Methods and Materials: A commercial anthropomorphic head phantom filled wit h water and containing CT, MR, and PET visible targets was modified to eval uate the accuracy of multimodality image registration and fusion software. For MR and PET imaging, the water inside the phantom was doped with CuNO3 a nd F-18-fluorodeoxyglucose (F-18-FDG), respectively. Targets consisting of plastic spheres and pins were distributed throughout the cranium section of the phantom. Each target sphere had a conical-shaped bore with its apex at the center of the sphere. The pins had a conical extension or indentation at the free end. The contours of the spheres, sphere centers, and pin tips were used as anatomic landmark models for image registration, which was per formed using affine coordinate-transformation tools provided in a commercia l multimodality image registration/fusion software package. Four sets of ph antom image studies were obtained: primary CT, secondary CT with different phantom immobilization, MR, and PET study. A novel CT, MR, and PET external fiducial marking system was also tested. Results: The registration of CT/CT, CT/MR, and CT/PET images allowed correl ation of anatomic landmarks to within 2 mm, verifying the accuracy of the r egistration software and spatial fidelity of the four multimodality image s ets. Conclusions: This straightforward phantom-based quality assurance of the im age registration and fusion process can be-used in a routine clinical setti ng or for providing a working image set for development of the image regist ration and fusion process and new software. (C) 2001 Elsevier Science Inc.