Dynamics of Metabolic Changes in Intracranial Metastases and Distant Normal-Appearing Brain Tissue after Stereotactic Radiosurgery: A Serial Proton Magnetic Resonance Spectroscopy Study

Abstract

The present study evaluated the dynamics of metabolic changes in intracranial metastases and distant normal-appearing brain after stereotactic radiosurgery (SRS). Forty neoplasms were evaluated with single-voxel proton magnetic resonance spectroscopy (¹H-MRS) both before and after treatment. From one to six examinations (median, 3) were done in each individual case during follow-up. At the time of each investigation additional ¹H-MRS was obtained from the normal-appearing brain distant from the radiosurgical target. Investigated metabolites included N-acetylaspartate (NAA), choline-containing compounds (Cho), creatine (Cr), and mobile lipids (Lip). Within the first month after SRS responded tumors showed a statistically significant increase in NAA/Cho ratio, and decrease of Cho content and Lip-to-normal brain Cr (nCr) ratio. By contrast, statistically significant metabolic alterations were not detected in stabilized tumors. Statistically significant volumetric and metabolic changes were not marked between three and 12 months after treatment in non-progressing lesions. Alternatively, decrease of NAA/Cho ratio, NAA content and Cr content, and increase in Lip/nCr ratio and Cho content were evident in progressive neoplasms, and subtle metabolic alterations could be revealed even before the increase in the lesion volume. Metabolic characteristics of normal-appearing brain distant from the radiosurgical target did not show statistically significant changes within the first year after treatment. In conclusion, additional use of serial ¹H-MRS during follow-up after SRS for intracranial metastases permits detailed evaluation of the metabolic tumor response and may be potentially helpful for early prediction of recurrence.