Early Changes In Proton Magnetic Resonance Spectroscopic Findings In Patients Receiving Three-stage Gkrs For Relatively Large Brain Metastatic Tumors

Keywords: Imaging, brain metastasis, magnetic resonance imaging, gamma knife, radiosurgery

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       The response to tumor radiosurgery is evaluated with imaging.
     We studied early changes on proton magnetic resonance spectroscopy (1H-MRS) in patients who underwent three-stage gamma knife radiosurgery (GKRS) for relatively large metastatic brain tumors.
      Among 45 brain metastasis patients who underwent three-stage GKRS with an interval of two weeks from 2005 to 2009, 13 (eight men, five women, mean age 62 range; 42-81 years) were selected for this study.
      All 13 patients (13 tumors) were assessed using multi-voxel 1H-MRS at least twice, before the first and third sessions. Seven patients received follow-up 1H-MRS studies at a median interval of 31 (range; 4-84) weeks. The most common primary tumor site was the lung, 10 patients, followed by breast, esophagus and thymus in one each. The mean pre-GKRS tumor volume was 20.7 (range; 9.9-30.8) cc. A 10 Gy peripheral dose was given in each of three sessions. We analyzed 1H-MRS-shown metabolites using a total of 113 voxels of which more than 60% of individual voxel volume was accounted for by a solid tumor component.
      Remarkable tumor volume reduction was seen between the first (mean; 20.7 cc) and third (mean; 9.5 cc) sessions. The volume reduction rate was 47.2%. The mean choline peak value before the first session (2.55+2.45) decreased significantly as compared to that before the third session (1.18+1.00, P<0.01) while there were no significant differences in metabolite peak values of N-acetyl-aspartate and creatine between the two sessions. Eight patients showed post-treatment tumor volume reductions while there were no remarkable changes in three. Due to early death, the other two patients did not receive follow-up MR examinations. In the seven patients assessed using 1HMRS after treatment, no marked changes in metabolite peak values were detected.
     This is a retrospective study.
     Three-stage GKRS produced remarkable tumor volume reduction during the four-week period between the first and third sessions in all cases and there was a subsequent post-treatment decrease in some cases.
     While choline peak values had decreased remarkably by the third session, thereafter, little change was seen.


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