MR perfusion characteristics of pseudoprogression in brain tumors treated with immunotherapy - a comparative study with chemo-radiation induced pseudoprogression and radiation necrosis.

Purpose: Pseudoprogression is an atypical imaging pattern of response to immunotherapy in patients with brain tumors. MR perfusion studies in this field are limited. The purpose of our study is to compare the perfusion features between pseudoprogression lesions in malignant gliomas and brain metastases treated with immunotherapy (iPsP) and the pseudoprogression after chemo-radiation therapy and radiation necrosis after radiation treatment (ChR-PsP & RN).

Methods: We retrospectively reviewed 25 iPsP lesions in 16 brain tumor patients and 48 ChR-PsP & RN lesions in 35 patients. The cerebral blood volume (CBV) of MR dynamic susceptibility contrast (DSC) perfusion weighted imaging (PWI) was analyzed, and the mean and maximal values of the ratio of CBV (rCBV and rCBV) of iPsPs and ChR-PsP & RNs were calculated and compared between these two groups using the Mann-Whitney U test. A receiver operating characteristic curve analysis was conducted, and the optimal cutoff of perfusion parameters were determined using the area under the curve, sensitivity, and specificity.

Results: The medians of rCBV and rCBV in iPsP group were significantly higher (0.94 and 1.39 respectively) than ChR-PsP & RN group (0.67, p < 0.01 and 1.1, p = 0.01 respectively). The rCBV value of 0.69 can differentiate the iPsP from ChR-PsP & RN with the area under the curve of 0.71, sensitivity of 0.72, and specificity of 0.56.

Conclusion: These findings may suggest immunotherapy-induced higher perfusion in the iPsP lesions compared to ChR-PsP & RN lesions in primary and metastatic brain tumors.