Decreased T2-signal intensities indicate positive response to front-line radiotherapy in pediatric low-grade gliomas

To evaluate MRI changes in T2-weighted imaging (T2WI) signal intensity (T2SI) as a potential imaging marker for assessing response to radiotherapy (RT) in pediatric low-grade glioma (pLGG).

This retrospective study analyzed imaging data of 56 pLGG patients (mean age, 12.4 ± 3.5 years; 33/56 [58.9%] male) treated with photon-based or proton-based RT within the SIOP-LGG 2004 study and registry. Tumor signal characteristics on T2WI were qualitatively and quantitatively assessed at baseline and up to 24 months post-RT. Tumor volumes were calculated, and correlations between ∆T2SI and volumetric changes were examined. Statistical tests included inferential tests, correlation analysis, and linear regression.

At baseline, 87.5% tumors were rated as hyperintense, while none was rated hypointense. The mean ratio between T2SI of the tumors compared to the cerebral cortex was 1.70. A significant decrease in T2SI was observed over time with the strongest decrease at 24 months post-RT (- 18.7%; p = 0.002). ∆T2SI correlated significantly with tumor volume reduction (r = 0.46, p < 0.001) and response assessment (ρ = 0.51, p < 0.001). There was no significant influence of age, sex, tumor location, histology, or RT type on ∆T2SI. Cases of pseudoprogression cases exhibited stable T2SI despite transient increases in contrast enhancement or tumor volume.

A reduction in T2SI was consistently associated with tumor volume reduction, suggesting that a decrease in T2SI may serve as an additional imaging marker of a positive response to RT in pLGG patients.