DEVELOPMENT OF AN MR SIMULATOR - EXPERIMENTAL-VERIFICATION OF GEOMETRIC DISTORTION AND CLINICAL-APPLICATION

PURPOSE: To evaluate the geometric distortion on magnetic resonance (M R) images obtained with a permanent magnet system and determine the us efulness 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-assi sted x-ray simulation was performed with skin markers in 14 patients w ith bone tumors. Treatment planning had already been performed with a conventional system. RESULTS: On phantom images, most of the positiona l displacements within a 120-mm radius from the center of the static m agnetic held were less than 2 mm; larger displacements were observed i n the peripheral region of the images. MR imaging was useful in the RT TP of all patients. The original radiation field was modified after MR examination in six patients. CONCLUSION: The amount of image distorti on within the practical area is acceptable for RTTP. MR imaging-assist ed x-ray simulation is useful for patients with bone tumors and warran ts further investigation.