Could lipid CH2/CH3 analysis by in vivo 1H MRS help in differentiation of tumor recurrence and post-radiation effects?

PURPOSE To inspect the potential diagnostic role of in vivo 1H MRS lipid methylene CH2 to methyl CH3 signal ratio in differentiation of recurrent brain tumor from radiation injury. METHODS Two patients--one with documented recurrence and the other without recurrence--were monitored by means of 1H MRS before and during two years after radiation therapy. The comparative group consisted of 20 patients with glial tumor recurrence diagnosed 2 years after the radiotherapy. RESULTS In case of tumor recurrence, an increase of the lipid CH2/CH3 value is observed. In contrast, for the patient with no tumor recurrence and within the brain areas distant from the tumor the CH2/CH3 ratio reveals a negative correlation vs. time after irradiation. The Lip trend to increase on radiotherapy both at the tumor bed and within the non-involved areas lessens the value of Lip as a marker of tumor recurrence. CONCLUSION The analysis of the lipid CH2/CH3 ratio may be useful in differentiation of the tumor recurrence from radiation response. The Lip signals observed in normally appearing brain tissue after radiotherapy could originate from the change of metabolism of irradiated cells.