Magnetic resonance spectroscopy imaging in radiotherapy planning for recurrent gliomaa)
MRSI voxels overlaid contrast enhanced T1-weighted MRI for patient 4 acquired (a) before the first cycle of bevacizumab. MRSI voxels with EMR were marked by the radiologist (). (b) Target definitions on an axial slice overlaid contrast enhanced T1-weighted MRI acquired before starting bevacizumab. The GTV (dark pink) is defined by the contrast enhancement on the CT and the pre- and post-T1-weighted MRI. MRSIpre (pink) and MRSIpost (green) are outline of MRSI voxels with EMR as determined from the pre- and post-MRSI. CTV (orange) is the CTV used for radiation treatment planning while “CTV per protocol” (purple) is the intended clinical target volume if no size limitation of the final treatment volume was considered.
Target volumes shown for all patients. The GTV, treatment CTV, and treatment PTV are the actual volumes used for HFSRT. Combined MRSI pre & post is the total volume of the MRSI voxels with EMR from the scans acquired before and after the first cycle of bevacizumab. Protocol CTV is given by GTV plus 5 mm margin plus all MRSI voxels with EMR.
Percent increase in CTV if all MRSI voxels with elevated metabolite ratios were included in the CTV.
Maximum dose to critical structures from previous and current radiation treatment plans.
Volume of MRSI voxels with EMR before (MRSIpre) and after (MRSIpos t) the first cycle of bevacizumab and GTV determined as the composite of the contrast enhancement on T1-weighted MRI before and after bevacizumab and the planning CT. GTVpos t is the contrast enhancement on T1-weighted MRI after bevacizumab. The GTVpos t volume was inside the GTV for all patients. The volume of MRSI voxels pre- and postbevacizumab outside the GTV + 5 mm (= CTV if no voxels showed EMR) are shown in the last two columns. Patients 8–12 had no MRSI voxels with EMR.
Pathology, 6-month PFS and OS for all 12 patients. Patients 1–7 had MRSI voxels with EMR, while patients 8–12 did not have any MRSI voxels with EMR on either of the MRSI scans.
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