RADI-43. ARTERIAL SPIN LABELING PERFUSION MR IMAGING FOR DIFFERENTIATION BETWEEN TUMOR RECURRENCE AND PSEUDOPROGRESSION IN INTRACRANIAL METASTASES FOLLOWING STEREOTACTIC RADIOSURGERY

Stereotactic radiosurgery (SRS) is a standard adjuvant treatment for patients with limited intracranial metastatic disease. Transient growth, increased peritumoral edema, and inflammation can be seen in up to a third of these cases following SRS. Unfortunately, this pseudoprogression is often indistinguishable from true progression by morphologic MR imaging thereby complicating patient management. The purpose of this study was to evaluate whether arterial spin labeling (ASL) perfusion can differentiate tumor recurrence from pseudoprogression after SRS. We reviewed patients treated between 2013 and 2018 and identified 24 patients with 43 intracranial metastases who had imaging suggesting progression following SRS and also had ASL perfusion acquired at time of MR imaging. Median imaging follow-up was 11 months (range 3–64 months). Outcome of tumor recurrence or pseudoprogression was confirmed in each case by pathology or subsequent MR imaging. 25 (58%) lesions were classified as tumor recurrence (13, 52% by pathology), while 18 (42%) were classified as pseudoprogression (3, 18% by pathology). ASL perfusion values (normalized cerebral blood flow) were higher in patients with tumor progression (2.1 vs 1.1 ml/min/100g, p=0.003). No significant difference was observed between histology, time from radiotherapy, marginal dose, volume of lesion, or instances of repeat SRS treatments between groups. In conclusion, elevated blood flow by ASL perfusion was closely associated with the diagnosis of tumor recurrence after SRS. Patients with intracranial metastases undergoing SRS may benefit from this short non-contrast sequence at time of follow-up MR imaging.