Purpose: In this study, we investigated fluorine-18 fluoromethylcholine (F-FCho) PET and contrast-enhanced MRI for predicting therapy response in glioblastoma (GB) patients according to the Response Assessment in Neuro-Oncology criteria. Our second aim was to investigate which imaging modality enabled prediction of treatment response first.
Materials and methods: Eleven GB patients who underwent no surgery or debulking only and received concomitant radiation therapy (RT) and temozolomide were included. The gold standard Response Assessment in Neuro-Oncology criteria were applied 6 months after RT to define responders and nonresponders. F-FCho PET and MRI were performed before RT, during RT (week 2, 4, and 6), and 1 month after RT. The contrast-enhancing tumor volume on T1-weighted MRI (GdTV) and the metabolic tumor volume (MTV) were calculated. GdTV, standardized uptake value (SUV)mean, SUVmax, MTV, MTV×SUVmean, and percentage change of these variables between all time-points were assessed to differentiate responders from nonresponders.
Results: Absolute SUV values did not predict response. MTV must be taken into account. F-FCho PET could predict response with a 100% sensitivity and specificity using MTV×SUVmean 1 month after RT. A decrease in GdTV between week 2 and 6, week 4 and 6 during RT and week 2 during RT, and 1 month after RT of at least 31%, at least 18%, and at least 53% predicted response with a sensitivity and specificity of 100%. As such, the parameter that predicts therapy response first is MR derived, namely, GdTV.
Conclusion: Our data indicate that both F-FCho PET and contrast-enhanced T1-weighted MRI can predict response early in GB patients treated with RT and temozolomide.