NI-20 * ADC HISTOGRAM ANALYSIS FOLLOWING RADIOTHERAPY PREDICTS RESPONSE TO ADJUVANT TEMOZOLOMIDE IN NEWLY DIAGNOSED GBM

Abstract

INTRODUCTION: The current standard of care for newly diagnosed GBM consists of concurrent radiotherapy and temozolomide (TMZ) plus adjuvant TMZ. We hypothesize there is a subset of patients that will have a significant benefit from this adjuvant therapy. Therefore, the purpose of the current study was to identify a diffusion imaging phenotype for patients with newly diagnosed GBM that will benefit from adjuvant TMZ following concurrent radiotherapy and TMZ. METHODS: A total of 120 patients with: 1) histologically confirmed glioblastoma, 2) treated with concurrent radiotherapy and TMZ followed by adjuvant TMZ; and 3) high quality diffusion MR data were included in the current study. Diffusion and standard structural MRI were performed approximately 10 weeks after the start of radiotherapy and concurrent TMZ. ADC histogram analysis was performed by fitting a double Gaussian mixed model to ADC data extracted from contrast enhancement tumor. ADCL was defined as the mean ADC of the lower Gaussian distribution. We hypothesize that patients with a high ADCL have a lower tumor burden and thus favorable response to adjuvant TMZ in terms of TTP and OS. RESULTS: Results demonstrate that patients with an ADCL lower than 1 um2/ms has a significantly shorter PFS compared with patients having a higher ADCL (Log-rank, P < 0.0001), showing almost twice the median PFS (297 days vs. 156 days). Additionally, patients with a high ADCL had a significantly longer OS (Log-rank, P = 0.0049). Patients with a high ADCL had a median OS of 648 days while patients with a low ADCL had a median OS of only 407 days from the start of adjuvant TMZ. CONCLUSION: Newly diagnosed GBM patients with elevated tumor diffusivity after completion of radiotherapy and concurrent TMZ have a favorable prognosis.