Correlation of Magnetic Resonance Imaging Apparent Diffusion Coeffecient Values with Treatment Outcome in High Grade Glioma Patients Undergoing Concurrent Chemoradiation

Abstract

High grade gliomas are aggressive malignancies characterized by high proliferation rate, extreme heterogeneity with potential to develop resistance to radiation and chemotherapy as well as short survival period. MRI is considered to be the best imaging modality for brain tumors. ADC values has the potential to serve as an imaging biomarker for response assessment, since it can provide dynamic objective information about tissue and tumor cell density. Low ADC values of diffusion weighted MRI in brain is a negative prognostic variable for patients undergoing radiotherapy. MRI ADC values could provide a reasonably good opportunity to predict the response earlier than conventional methods and thereby could help in individualizing therapy. A total of 22 consecutive postoperative high-grade glioma patients (20 glioblastoma and 2 anaplastic astrocytoma) were analyzed. The ADC values of the tumor on pre-radiotherapy and post radiotherapy MRI were determined from several regions of interest defined in the tumor by “segmentation technique”. This technique expected to give more information, since it measures differing values within the tumor, which would be otherwise averaged out. Radiotherapy along with concurrent chemotherapy was undertaken in all cases. All the patients had at least one post radiotherapy MRI done. Kaplan -Meir survival curves, log rank test were used to evaluate the prognostic factors. The 18 months survival rates associated with low (<0.7x10-3mm2/sec) and high (>1.0x10-3mm2/sec) minimum pre-RT ADCs were 5 and 18 months respectively (p=0.004).The median follow-up period is 13 months. The patients with post RT minimum ADC value below 0.9 x10-3mm2/sec had median survival of 6 months and patients with post RT minimum ADC value above 0.9x10-3mm2 /sec had median survival of 15 months (P value = 0.040). The patients with post RT overall ADC value below 1.3 x10-3mm2/sec had median survival of 6 months and patients with post RT overall ADC value above 1.3x10-3mm2 /sec had median survival of 15 months (P value of 0.04). In high grade glioma patients who have tumors with low ADC values are expected to have have poorer prognosis. In our study of segmentation technique, the minimum ADC values showed better correlation with survival than overall ADC. The minimum ADC at pre-treatment MR imaging is a useful clinical prognostic biomarker. The minimum and overall ADC values from post treatment MR imaging are useful for patient risk stratification after completion of chemo radiation.In future, advanced imaging with new algorithms for 3D ADC mapping diffusion MRI might help in identification of the resistant sub-volumes within the tumor dynamicallly which can lead to biological targeted therapy.