MRI assisted radiotherapy planning

To obtain the optimal radiation field, an MR simulation system (MRSS) has been developed. The system consists of an MR unit, a work station and a laser marking system. Phantom study concerned geographic distortion and the total accuracy of MRSS, the former revealed the result lesser than 1 mm within 90 mm-distance between MR slices and Center of magnetic field, the latter showed maximal errors 2 mm in the field size, and 3 mm in the iso-center. This system was applied to 15 patients with intracranial or head and neck lesions and all procedures were smoothly performed. To evaluate the usefulness of MRSS, 6 radiation oncologists compared the difference between MRSS and CT simulation system in setting radiation field. The results were satisfactory especially in cases with lesions the extent of which was unclear on CT images. It was considered that this system could support the radiotherapy planning for intracranial or head and neck lesions. (author)