Radiosurgical treatment planning of brain metastases based on a fast, three-dimensional MR imaging technique

A fast, three-dimensional (3D) sequence for magnetic resonance (MR) imaging of the brain and its application in radiosurgical treatment planning of brain metastases is reported. The measuring sequence (MPRAGE) requires magnetization-prepared 180 degrees inversion pulses followed by rapid low angle excitation pulses and gradient-echoes for image generation. The resulting T1-weighted MPRAGE images were compared with two-dimensional (2D) T1-weighted spin-echo (SE) images after administration of 0.1 mmol/kg b.w. Gd-DTPA in 10 patients with known brain metastases. Original or multiplanar reformatted images obtained from a 128 partition data set of the 3D MPRAGE sequence offered comparable diagnostic quality to that of 2D SE imaging. Gd-DTPA enhancement and lesion targeting was similar in most of the patients in SE as well as MPRAGE imaging. During imaging and therapy the patient's head was fixed in a stereotactic localization system which is usable at the MR and the linear accelerator installations. The dose calculation of the radiosurgery planning was based on 3D MR imaging data assuming a homogenous attenuation value inside the head which was sufficient for an accurate dose calculation since tissue inhomogeneities do not significantly influence the shape of the relative dose distribution especially for radiosurgery of the brain. Under this circumstance the dose calculation can be based only on the 3D geometric conformation of the patient's head. A simple algorithm for treatment planning can be used if the MR data are free of geometric distortion.(ABSTRACT TRUNCATED AT 250 WORDS)