We have observed in patients with brain metastases (BM) that additional lesions are routinely detected on very high resolution stereotactic MR imaging as compared to routine diagnostic MR imaging. We hypothesized that these additional lesions represent the majority of distant recurrences found on new images within 6 months following radiosurgery should conventional stereotactic imaging have been used.

     We compared the diagnostic and high resolution stereotactic MR images of all 854 patients with BM who had no prior treatment and who were treated in our center between June 2002 and June 2009. Of these patients, 502 presented with 1 BM, 213 with 2, 85 with 3, 38 with 4 and 16 with more than 4 BM.

     All BM were diagnosed on routine diagnostic MR imaging performed no longer than 1 month prior to Gamma Knife® radiosurgery (GKRS). GKRS planning was based on stereotactic MR with scan matrix 256 x 256 with consecutive 1,5 mm 3-D gradient T1W images with triple-dose gadolinium.

     At least one additional lesion was found in 341 (40%) of the 854 patients. Of the 502 patients who presented with 1 BM on the diagnostic MR imaging, 151 patients (30%) had more BM on the high resolution MR imaging for GKRS planning. In those patients who presented with 2, 3, 4 and more than 4 BM, additional lesions were found in 103 (48%), 49 (58%), 24 (63%) and 14 (88%) patients, respectively. The new brain metastases free survival was 38% at 6 months. This percentage is similar to what is reported following radiosurgery, based on stereotactic CT or conventional MRI followed by WBRT.

     This is a retrospective study.

     Gamma Knife radiosurgery of additional BM found on very high resolution stereotactic MR imaging is as efficient to prevent new BM as prophylactic WBRT added to radiosurgery based upon conventional stereotactic imaging.