Distortion inherent to magnetic resonance imaging can lead to geometric miss in radiosurgery planning

Abstract

Purpose Anatomic distortion is present in all MRI data due to non-linearity of gradient fields and measures up to several millimeters. We evaluate the potential for uncorrected MRI to lead to geometric miss of the target volume in stereotactic radiosurgery (SRS). Methods and Materials Twenty-eight SRS cases were studied retrospectively. MRIs were corrected for gradient non-linearity distortion in three dimensions, and gross tumor volumes (GTVs) were contoured. The manufacturer-specified distortion field was then re-applied to GTV masks to allow measurement of GTV displacement in uncorrected images. The uncorrected GTV was used for SRS planning, and the dose received by the true (corrected) GTV was measured. Results Median displacement of the GTV due to gradient distortion was 1.2 mm (interquartile range 0.1 mm – 2.3 mm), with a minimum of 0 mm and a maximum of 3.9 mm. Eight of the twenty-eight cases met a priori criteria for “geometric miss.” Conclusions While MRI distortion is often subtle on visual inspection, there is a significant clinical impact of this distortion on SRS planning. Distortion-corrected MRI should uniformly be used for intracranial radiosurgery planning because uncorrected MRI can lead to potential geometric miss.

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