Prognostic value of 18F-FET PET imaging in re-irradiation of high-grade glioma: Results of a phase I clinical trial.

Background and purpose Positron emission tomography (PET) provides quantitative metabolic information and potential biomarkers of treatment outcome. We aimed to determine the prognostic value of early 18 F-fluoroethyl-tyrosine ( 18 F-FET) PET scans acquired during re-irradiation for recurrent high-grade glioma (HGG). Material and methods A phase I clinical trial of re-irradiation of HGG was carried out. MRI and 18 F-FET PET were used for target delineation and follow-up. Images were acquired at baseline, during radiotherapy and 4 weeks post-treatment and compared by measuring the metabolically active biological tumor volume (BTV) and maximal activity ( T max / B ). Correlations with outcomes were assessed by multivariate Cox regression analysis. Results Thirty-one patients were included and all patients have died. The median overall survival was 7.0 mos. Both baseline BTV and baseline MRI volume (necrotic/cystic cavities subtracted) were prognostic for overall survival (OS) in multivariate analysis (HR = 1.3 p < 0.01 and HR = 1.3 p < 0.01, respectively). Early changes in BTV and T max / B were observed but they carried no independent prognostic information. Conclusions Baseline biological tumor volume (BTV) defined by 18 F-FET PET was prognostic for OS in multivariate analysis, as was MRI volume (necrotic/cystic cavities subtracted). Tumor volume may aid in identifying patients whose life expectancy is too short to warrant re-irradiation. [ABSTRACT FROM AUTHOR]