PO20
VOXEL-BASED PARAMETRIC RESPONSE USING THE SERIAL MEASUREMENT OF APPARENT DIFFUSION COEFFICIENT FOR PREDICTING SUBSEQUENT TREATMENT RESPONSE PATTERN IN PATIENTS WITH GLIOBLASTOMA Free

INTRODUCTION: Determining treatment response after concurrent chemoradiotherapy (CCRT) in glioblastoma is important to minimize morbidity and the financial burden associated with prolonged ineffective treatment. We performed this study to determine the diagnostic superiority of apparent diffusion coefficient (ADC) parametric response (ADCPR) for predicting glioblastoma treatment response, compared to single time point measurement. METHOD: 50 post-treatment glioblastoma patients were enrolled. ADCPR was calculated from serial ADC maps acquired before and at the time of first detection of an enlarged contrast-enhancing lesion on voxel-by-voxel basis. The percentage-decrease in ADCPR and 10% histogram cutoff of ADC (ADC10) were compared as potential predictors of treatment response at subsequent 3 months and 1 year follow-up studies. RESULTS: The percentage-decrease in ADCPR was significantly higher in progression group than in stable-response group both at 3 months follow-up studies (p <.001) and at 1 year follow-up studies (p = 0.003-0.002). ADCPR significantly improved area under the receiver operating characteristic curve from 0.67 to 0.88 and from 0.70 to 0.92 for both readers, respectively, compared to ADC10 at 3 months follow-up studies but did not significantly improve at 1 year follow-up studies. The interreader agreement was higher for ADCPR than ADC10 (intraclass correlation coefficient, 0.93 versus 0.86). CONCLUSION: Voxel-based ADCPR appears to be a superior imaging biomarker than single time point measurement of ADC particularly for predicting early tumor progression in patients with glioblastoma.