Radiation Effects on Normal Brain in Subjects With Recurrent Glioblastoma by Spectroscopic MRI.

Area of Science:

• Neuro-oncology
• Radiology
• Biochemistry

Background:

• Glioblastoma (GBM) is an aggressive primary brain tumor with a high recurrence rate.
• Conventional MRI struggles to differentiate recurrent GBM from treatment effects.
• Spectroscopic MRI (sMRI) offers metabolic information, with choline (Cho) and N-acetylaspartate (NAA) ratios used to assess tissue abnormality.

Purpose of the Study:

• To investigate if prior radiation therapy (RT) alters baseline metabolic ratios in recurrent GBM.
• To determine the relationship between radiation dose and metabolite levels (Cho, NAA, Cr) in recurrent GBM.
• To assess the potential of dose-corrected metabolic maps for improved tumor delineation.

Main Methods:

• Retrospective analysis of 20 recurrent GBM patients treated with surgery, RT, and temozolomide.
• Whole-brain sMRI performed at recurrence, with co-registration to radiation dose maps.
• Voxel-wise linear regression to correlate radiation dose with normalized Cho/NAA, NAA, and Cr levels.

Main Results:

• Higher prior RT dose was significantly associated with reduced NAA and Cr levels.
• Cho levels showed minimal change with increasing radiation dose.
• Normalized Cho/NAA ratio increased with radiation dose (0.0018/Gy), indicating a shift in metabolic profile.

Conclusions:

• Prior RT modestly elevates the baseline Cho/NAA ratio in recurrent GBM, primarily due to NAA reduction.
• Standard Cho/NAA thresholds may misinterpret irradiated tissue as metabolically abnormal.
• Dose-corrected Cho/NAA maps could enhance the accuracy of tumor delineation in recurrent GBM.