A study on the magnetic resonance imaging (MRI)-based radiation treatment planning of intracranial lesions

Abstract

The aim of this study is to develop a magnetic resonance imaging (MRI)-based treatment planning procedure for intracranial lesions. The method relies on (a) distortion correction of raw magnetic resonance (MR) images by using an adaptive thresholding and iterative technique, (b) autosegmentation of head structures relevant to dosimetric calculations (scalp, bone and brain) using an atlas-based software and (c) conversion of MR images into computed tomography (CT)-like images by assigning bulk CT values to organ contours and dose calculations performed in Eclipse (Philips Medical Systems). Standard CT + MRI-based and MRI-only plans were compared by means of isodose distributions, dose volume histograms and several dosimetric parameters. The plans were also ranked by using a tumor control probability (TCP)-based technique for heterogeneous irradiation, which is independent of radiobiological parameters. For our 3 T Intera MRI scanner (Philips Medical Systems), we determined that the total maximum image distortion corresponding to a typical brain study was about 4 mm. The CT + MRI and MRI-only plans were found to be in good agreement for all patients investigated. Following our clinical criteria, the TCP-based ranking tool shows no significant difference between the two types of plans. This indicates that the proposed MRI-based treatment planning procedure is suitable for the radiotherapy of intracranial lesions.

Distortion Inherent to Magnetic Resonance Imaging (MRI) Can Lead to Geometric Miss in Radiosurgery Planning

“…Our findings demonstrate that using uncorrected MRI to delineate brain targets may yield contours that are displaced from the actual target position by several millimeters. This finding is consistent with the degree of distortion measured in previous MR studies [6,[10][11][12]. For highly conformal plans, such as those used in SRS, our findings suggest that those several millimeters are enough to result in considerable under-dosing of the true target or tumor.…”

“…Therefore, the results cannot be used to make extrapolations to predict the prevalence of the problem in the general population, though the degree of distortion measured here is consistent with previous studies [6,10,11]. To avoid differences in the magnitude of distortion across different scanners, our data all come from one scanner-though it is a modern MR system from a popular vendor, and gradient non-linearity is known to affect all MRI [4,5,8,9,13].…”

“…This non-linearity is more severe on newer scanners with faster and more powerful gradient coils at the expense of intentionally compromising linearity [8,9]. The magnitude of gradient non-linearity distortion has generally been reported up to 4-6 mm-with some reports of greater than 10 mm-and often represents the largest source of uncorrected distortion [6,[10][11][12].…”

Generating patient specific pseudo-CT of the head from MR using atlas-based regression

“…Either one can directly register an atlas CT to the target MR image (Schreibmann, Nye, Schuster, Martin, Votaw & Fox 2010) or one can relate them through an atlas MR that has previously been registered to a CT (Dowling, Lambert, Parker, Salvado, Fripp, Capp, Wratten, Denham & Greer 2012). When the latter approach is used for segmentation it is often referred to as atlas-based segmentation (Stanescu, Jans, Pervez, Stavrev & Fallone 2008). Because atlas-based methods rely heavily on prior information, they are more robust, and are therefore better equipped to deal with image artifacts such as those caused by metal implants.…”

A preplanning method for stereotactic radiosurgery to improve treatment workflow

“…Multiple groups have been extensively studied the use of MRI alone as the basis for treatment planning 18 , 19 , 20 . Most of the studies make a substantial effort to extract accurate CT numbers and to address potential geometric distortions.…”