Evaluation of Response to Stereotactic Radiosurgery in Brain Metastases Using Multi parametric. (31st January 2018) - Sawlani, Vijay
Abstract: PurposeConventional MRI methods are insufficient to accurately differentiate between local tumour recurrence and radiation-induced necrosis. Advanced MRI techniques such as perfusion imaging, diffusion imaging and spectroscopy have individually been shown to aid the assessment of response following SRS treatment of brain metastases [1–3]. However, the potential added-value of a multi-parametric approach using a combination of these techniques has not been investigated. Materials and MethodsA retrospective analysis was performed on 10 multi-parametric MRI examinations following SRS for metastatic brain lesions in a cohort of 7 patients with varying primary malignant diseases (melanoma, n=3; breast, n=3; small cell lung, n=1). Multi-parametric MRI examination consisted of dynamic susceptibility contrast (DSC) perfusion imaging, diffusion weighted imaging (DWI) and both single- and multi-voxel MR spectroscopy (MRS) (TE = 30 ms). Relative cerebral blood volume (rCBV) and apparent diffusion coefficient (ADC) maps were calculated from DSC and DWI data respectively using Siemens Syngo software and an rCBV ratio (lesion: contralateral) calculated. Analysis of MRS was performed using TARQUIN [4]. Correlations between rCBV ratio, ADC and Cho:Cr were investigated. Predictions of response based on each parameter were tested using radiological and clinical follow up. ResultsCho:Cr demonstrates a strong positive correlation with rCBV ratio (r = 0.89, p < 0.01). This is in agreement with previous work in pre-treatment metastases [5]. No significant correlations were observed between ADC and rCBV or Cho:Cr. Applying a reported threshold for rCBV ratio of 2.1 [1], patients were divided into two groups showing suspected tumour recurrence (n=4) and suspected radiation necrosis (n=3). ConclusionPreliminary results suggest that a combination of high rCBV, low ADC and high Cho: Cr can clearly identify local tumour recurrence and that multi-parametric MRI may show improved accuracy compared with any of the techniques in isolation.