Pseudoprogression is frequent following front-line radiotherapy in pediatric low-grade glioma – results from the German LGG cohort

Abstract

Purpose

Expansion of MRI T2- and/or T1-tumor lesion volume after radiotherapy (RT) may indicate pseudoprogression (PsPD). The differentiation between true progression and PsPD is a clinical challenge and under-investigated in pediatric low-grade glioma (LGG). We evaluated radiological criteria for PsPD following front-line RT and investigated the frequency and duration of PsPD following three RT-modalities within the framework of the [Anonymized for Review] LGG-studies.

Methods

Baseline and follow-up MRI-scans of 136 patients (72 [52.9%] male, median age at start of RT 11.3 years [range 0.8-25.9]) of the [Anonymized for Review] cohorts (¹²⁵iodine-interstitial RT [IS; n=51], photon-beam [XRT; n=60] or proton-beam RT [PBT; n=25]) were centrally evaluated for: Increasing 1) total tumor-associated T2-lesion, 2) focal tumor-associated T2-lesion and 3) contrast-enhancing tumor over a period of 24 months following RT. The pattern of these criteria initiated "suspicion" of PsPD, their evolution determined "definite" PsPD.

Results

Definite PsPD was radiologically determined in 54/136 (39.7%) without differences in frequency between RT-modalities: IS 22/48 vs. XRT 24/54 vs. PBT 11/20; p=0.780. Definite PsPD occurred at median 6.3 months (IS 7.2 months; XRT 4.4 months; PBT 6.5 months) after RT-initiation and persisted for median 7.2 months (IS 8.5 months; XRT 7 months; PBT 7.4 months). Appearance of necrosis within the focal tumor-associated T2-lesion proved to be a relevant associated predictor of definite PsPD (p<0.001).

Conclusions

PsPD is frequent following irradiation of pediatric LGG and independent of the RT-modality (IS vs. XRT vs. PBT). Adequate identification of PsPD versus true progression is imperative to prevent unneeded salvage treatment.