Magnetic resonance spectroscopy imaging in radiotherapy planning for recurrent glioma

Purpose: The purpose of this study was to investigate how incorporation of magnetic resonance spectroscopy imaging (MRSI) into radiotherapy planning would increase the target volume for patients with recurrent glioma. Methods: After prior standard radiotherapy, 25 patients with recurrent glioma were treated with bevacizumab and concurrent hypofractionated stereotactic radiotherapy (HFSRT), delivering 30 Gy in five fractions. MRSI were acquired for 12 patients. Areas with markedly higher choline levels relative to the levels of total creatine and N-acetylaspartate were identified and referred to as MRSI voxels with elevated metabolite ratios (EMR). Gross tumor volume (GTV) consisted of contrast-enhancing tumor on T1-weighted magnetic resonance images (MRI) and computed tomography. Clinical target volume (CTV) was GTV+5 mm margin and MRSI voxels with EMR. Overall survival (OS) and 6-month progression free survival (PFS) for these patients were reported in a prior publication [Gutin , Int. J. Radiat. Oncol., Biol., Phys. 75 (1), 156-163 (2009)], and the outcome was correlated with the GTV and the volume of MRSI voxels with EMR in this study. Results: Seven of the 12 patients had MRSI voxels with EMR. If none of the MRSI voxels with EMR were included, the CTV would range from 9.2 to 73.0 cm 3 with a median of 31.0 cm 3 , whereas if all voxels were included, the CTV would range from 27.4 to 74.4 cm 3 with a median of 35.0 cm 3 . For three of the seven patients, including the voxels with EMR, would have increased the CTV by 14%-23%. For one patient, where the MRSI voxels with EMR did not overlap the GTV, including these voxels would increase the CTV by 198%. No correlation could be found between the OS and PFS and the GTV or the volume of MRSI voxels with EMR. Conclusions: Seven of 12 patients with recurrent glioma had MRSI voxels with EMR. For four of these seven patients, including the MRSI voxels with EMR, significantly increased the CTV. This study does not have statistical power to conclude on the importance of including areas with MRSI-suspect disease into the radiation target volume.