81 Using CCA-MRI to Predict Response to Stereotactic Radiosurgery in Patients with Brain Metastases

Abstract Introduction CCAs are obtained by subtracting T1-weighted MRI sequences at 5 and 60 minutes. This creates a colour-map representing how contrast is cleared in tissues over time. Generally, blue demonstrates rapid contrast-clearance suggesting active tumour whilst red represents delayed clearance indicating poor/damaged vasculature. This has been widely used post-SRS treatment to help differentiate between tumour progression and radionecrosis. Different tumours have varying radionsenstivities based on differences in their radiobiology including levels of oxygenation and vascularity. In this study we have used CCA imaging pre-SRS to determine if the vascularity and contrast handling capacity differs between different histologies offering a potential insight into whether this may influence radioresistance and SRS response. Methods 24 patients with 124 metastases of varying histology had pre-SRS CCAs. Radiotherapy-planning-CT scans were fused with the planning-post-contrast-T1-MRI, with consultant clinical oncologist-approved contoured targets, and the CCA-images. Threshold analysis was performed to obtain proportions of red and blue within the enhancing areas of each tumour. Results Preliminary results from the first 10 patients have shown that there is significant variability between the proportions of blue and red in brain metastases (p = 0.0294) from varying tumour histologies as well as intra patient variability. We are currently analysing the next 14 patients to increase the robustness of our findings.