Development of an MR simulator: experimental verification of geometric distortion and clinical application.

PURPOSE: To evaluate the geometric distortion on magnetic resonance (MR) images obtained with a permanent magnet system and determine the usefulness of MR imaging-assisted x-ray simulation in radiation therapy treatment planning (RTTP). MATERIALS AND METHODS: The authors measured the distortion on MR images of grid-pattern phantoms. MR imaging-assisted x-ray simulation was performed with skin markers in 14 patients with bone tumors. Treatment planning had already been performed with a conventional system. RESULTS: On phantom images, most of the positional displacements within a 120-mm radius from the center of the static magnetic field were less than 2 mm; larger displacements were observed in the peripheral region of the images. MR imaging was useful in the RTTP of all patients. The original radiation field was modified after MR examination in six patients. CONCLUSION: The amount of image distortion within the practical area is acceptable for RTTP. MR imaging-assisted x-ray simulation is useful for patients with bone tumors and warrants further investigation.