• James R Knitter, William K Erly, Baldassarre D Stea, Gerald M Lemole, Isabelle M Germano, Amish H Doshi, and Kambiz Nael.
• 1 Department of Medical Imaging, The University of Arizona College of Medicine, Tucson, AZ.
• AJR Am J Roentgenol. 2018 Jul 1; 211 (1): 168-175.

ObjectiveApparent increases in the size of cerebral metastases after stereotactic radiosurgery (SRS) can be caused by pseudoprogression or true disease progression, which poses a diagnostic challenge at conventional MRI. The purpose of this study was to assess whether interval change in DWI and perfusion MRI parameters can differentiate pseudoprogression from progressive disease after treatment with SRS.Materials And MethodsPatients with apparent growth of cerebral metastases after SRS treatment who underwent pre- and post-SRS DWI, dynamic susceptibility contrast (DSC)-MRI, and perfusion dynamic contrast-enhanced (DCE)-MRI were retrospectively evaluated. Final assignment of pseudoprogression or progressive disease was determined at 6-month follow-up imaging using the Response Assessment in Neuro-Oncology Brain Metastases criteria. Mean values of apparent diffusion coefficient (ADC), DCE-MRI-derived volume transfer constant (Ktrans), and DSC-MRI-derived relative cerebral blood volume (CBV) from pre- and post-SRS MRI scans were compared between groups using univariate and regression analysis. Fisher exact test was used to compare interval change of imaging biomarkers.ResultsOf 102 cerebral metastases evaluated, 32 lesions in 29 patients met our inclusion criteria. The mean duration of follow-up was 7.2 months (range, 6-14 months). Twenty-two lesions were determined as pseudoprogression, and 10 lesions were determined as progressive disease using the Response Assessment in Neuro-Oncology Brain Metastases criteria at 6-month follow-up MRI. The interval change pattern of our imaging parameters matched the expected patterns of treatment response for ADC (23/32 lesions; 72%; p = 0.055; odds ratio, 5.1), Ktrans (24/32 lesions; 75%; p = 0.006; odds ratio, 19.2), and relative CBV (27/32 lesions; 84%; p = 0.001; odds ratio, 25.3).ConclusionPseudoprogression can be distinguished from disease progression in cerebral metastases treated with SRS via an interval decrease in relative CBV and Ktrans values.

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