A volumetric analysis of timing and duration of T2/FLAIR changes on MRI following radiation therapy in patients with low-grade IDH-mutant glioma.

Background: Patients with IDH-mutant low-grade glioma (LGG) can achieve many years of survival with radiation (RT) and chemotherapy. There is a risk of overtreatment and negative treatment side effects if these patients are unnecessarily retreated due to perceived tumor progression in the absence of true tumor regrowth. A better understanding of volumetric postradiation FLAIR changes will help with the clinical interpretation of disease progression/treatment effect and will help guide management decisions. We conducted this research to characterize the changes in MRI FLAIR hyperintensity that occur in LGG patients following RT, to better understand the radiation-treatment effects or "pseudoprogression" that occurs in the absence of true tumor regrowth.

Methods: Serial MRI scans of patients with LGG were reviewed, including pre-RT and for 2.5 years post-RT. Segmentation for volumetric analysis was performed with manual supervision using ITK-SNAP (open-source segmentation software). Descriptive statistics are reported.

Results: Sixteen patients with histologic grade 2 gliomas were included. 159 MRI scans were segmented using ITK-SNAP (median 9.5 MRIs/patient). Nine of 16 MRIs showed decreasing FLAIR volume immediately post-RT, while 7/16 showed increasing FLAIR volume. After the initial post-RT MRI, 12/16 patients had MRIs with an increase in FLAIR volume sometime during the first year. The FLAIR volume stabilized or decreased a median of 18.4 months and a mean of 15.0 months post-RT.

Conclusions: FLAIR hyperintensity changes on MRI are highly variable in the first 1.5 years post-RT in low-grade glioma, but after 1.5 years, FLAIR volumes stabilize and decrease, likely indicating the inflection point where post-RT pseudoprogression stabilizes.