Peritumoral Apparent Diffusion Coefficient as a Metric of Response in Patients with Recurrent Glioblastoma Multiforme Treated with Bevacizumab and Irinotecan

Abstract

Bevacizumab and irinotecan have shown promising results in patients with recurrent glioblastoma multiforme (GBM), which traditionally carries a poor prognosis after first-line therapies have been exhausted. Retrospectively documenting the short-term effects of this chemotherapeutic regimen on recurrent GBM, as evidenced by comparative magnetic resonance images obtained two weeks prior to, and one-month following initiation of treatment, we hypothesize that peritumoral apparent diffusion coefficient (ADC) values will decrease on post-treatment scans. Brain MR data were collected from August 2005 to December 2006, in which post-contrast T1-weighted images demonstrated measurable enhancement or GBM tumor mass. Pre- and post-treatment MR images for ten consecutive patients were collected, each having failed temozolomide and radiation therapy. Pre- and post-treatment recurrent GBM bulk tumor and peritumoral T2 signal abnormality were measured in three dimensions. Diffusion of peritumoral T2 signal abnormality was evaluated on pre- and post-treatment ADC. All patients witnessed a significant decrease in tumor bulk ranging from 15.3% to 96.7% with a mean reduction of 48.2%, having received an average of two cycles of chemotherapy. FLAIR images demonstrated a mean volumetric reduction in peritumoral T2 signal abnormality of 44.3%. ADC measurements demonstrated an average reduction in peritumoral ADC of 20.6%, which was statistically significant (p-value < .005). Recurrent GBM tumor bulk demonstrated a 48.2% mean reduction, with corresponding decrease in peritumoral ADC values of 20.6%, suggesting that ADC may represent a valuable metric in the evaluation of the chemotherapeutic response of recurrent GBM, when treated with bevacizumab and irinotecan.