H magnetic resonance spectroscopy assessment of the temozolomide response in peaditric pilocytic astrocytomas

ABSTRACT

Pilocytic Astrocytomas (PA) treatment and prognosis is variable depending on location. ¹H Magnetic Resonance Spectroscopy (MRS) is used to characterize tumor metabolism providing additional information to the Magnetic Resonance Imaging (MRI) evaluation assessing the therapy response. This study was designed to evaluate brain metabolic changes that result from Temozolomide (TMZ) administration on pediatric PA using MRS. Twenty children with PA were studied. We performed MRI and MRS pretreatment and after 12 months of therapy on a 3.0 Tesla scanner in order to monitor the chemotherapy response to 5-day treatment with oral TMZ (200 mg/mt² x day) given every 28 days for 12 cycles. Multivoxel Proton Spectroscopic Imaging was performed using a Point Resolved Spectroscopy sequence (PRESS). Analysis of Variance (ANOVA) was applied to the results in order to evaluate the possible statistical differences. Pairwise comparisons with Bonferroni correction test were assessed in order to verify the differences among ratio means. It was observed a significant decrease in Cho/Cr ratio (p<0.05) and a significant increase in NAA/Cr ratio (p<0.05) while TMZ therapy was taking place. These results are linked with tumor size reduction (r = 0.95, p< 0.05) detected by MRI. Results show MRS can detect early tumor reaction to therapy prior to MRI. Therefore, MRS could provide a useful tool to monitor the answer of pediatric PA to TMZ. The link between metabolic markers changes due to TMZ treatment assessed by MRS and the tumor volume reduction may also provide a fertile ground to developa TMZ-based therapy for pediatric PA and to predict its efficacy to improve PA’s response to treatment.