NI-25 * PHYSIOLOGIC IMAGING IN PATIENTS WITH BRAIN METASTASES; HETEROGENEITY BASED UPON PRIMARY TUMOR SUBTYPE

Abstract

BACKGROUND: Structural and biologic tissue characteristics prior to and following radiosurgery (SRS) can be quantified by analyzing physiologic imaging sequences including diffusion and perfusion weighted imaging (DWI, PWI) and considering their derived parameters including apparent diffusion coefficient (ADC) and relative cerebral blood volume (rCBV). Increasingly in neuro-oncology, these types of imaging sequences are being considered as prognostic and diagnostic markers. Patients' primary tumor type may impact these imaging values, and an understanding of how baseline DWI and PWI measures depend upon primary tumor type is necessary in order to consider how these markers may impact therapeutic response or when considering diagnostic possibilities such as radiation necrosis. METHODS: 78 patients with 187 brain metastases were identified retrospectively from a cohort of patients who underwent SRS between August, 2011 and March 2014 at two institutions. Included subjects had undergone MRI with physiologic (DWI and PWI) imaging prior to SRS. The physiologic sequences were processed and co-registered to anatomic sequences acquired on the day of treatment. Lesions were segmented and ROIs were generated for image analysis using the T1 + Gd sequence. Quantitative measures included rCBV, rCBF, ADC and tumor volume for each lesion. Tumor subtypes included breast, lung, colon, melanoma, renal cell, ovarian, and “other”. RESULTS AND CONCLUSIONS: There was no significant difference in tumor volume based upon tumor type, although there was a trend toward larger tumors at diagnosis for colon and ovarian primaries. There was no significant difference in ADC between tumor type; a significant elevation in rCBV was seen for renal cell and ovarian primary tumors (2.51 and 2.46) when compared with breast, colon, melanoma and lung primary tumors (1.18, 1.24, 1.38, 1.27, respectively). When considering questions of diagnostic specificity, it is important to recognize the relatively low rCBV in many active brain metastases, particularly as compared with primary brain tumors.