Session Item

Several pathophysiological processes other than disease progression may give rise to contrast enhancing lesions on MRI imaging after radiotherapy for low grade glioma. Whether these lesions are indicative of dose-dependent tissue damage is subject of debate, especially after proton radiotherapy. However, data on contrast enhancing lesions after photon radiotherapy is scarce and their interpretation is often heterogeneous. We investigated new contrast enhancing lesions in a multicenter cohort of historical patients with IDH mutated grade 2 diffuse glioma treated with photon therapy, using a strict definition of pseudoprogression (psPD) and disease progression (PD).

Patients with histologically confirmed IDH-mutated diffuse grade 2 glioma treated with 50.4Gy between 1-1-2007 and 31-12-2018 were eligible for this study. Patients were treated in two tertiary referral centers. All MRI’s acquired between radiotherapy and PD were included and reviewed in the study. PD was defined in accordance with the RANO criteria. PsPD was defined as any new contrast-enhancing lesions between end of radiotherapy and PD, or any new contrast-enhancing lesion that remained stable over a period of 12 months in patients who did not exhibit PD. Lesions were described as transient if resolution was observed during follow-up, and persistent if no resolution was observed until PD or end of follow-up. Duration of psPD was defined as time between first and last MRI that showed psPD. Kaplan Meier estimates were used for overall survival from diagnosis (OS) and progression free survival (PFS) from end of radiotherapy.

A total of 106 patients were eligible and 931 MRI’s were analyzed. Median number of MRI’s per patient was 8 (range 1 – 25). Median follow up duration from radiotherapy was 3.8 years (range 0.3 – 12.7). A 1p19q codeletion was present in 46 patients (43.4%), absent in 53 patients (50.0%), and unknown in 7 patients (6.6%). Adjuvant chemotherapy was given to 52 patients (49.1%). At the time of analysis, median OS  was 10.7 years (95% CI 8.3 – 12.9) and median PFS was 5.9 years (95%  4.9 – 7.0). PsPD  was observed in 29 patients (27.4%) on at least one MRI. Median onset of psPD was 8.4 months (range 0.9 -137.2). In patients with psPD, 9 patients (31%) were found to have psPD on one MRI while 20 patients (69%) showed psPD over multiple MRIs (median 3, range 2-11). Median duration of all psPD was 6.2 months (range 0 – 53.5). PsPD was transient in 22 of 29 patients (79.2%). Median duration of transient psPD was 4.5 months (range 0 - 53.5). 

This study confirms psPD occurs frequently in patients with IDH-mutated low grade after treatment with photon radiotherapy. Although most PsPD occurs early in follow-up a delayed presentation is also seen, possibly reflecting different pathophysiologic processes. Awareness and identification of PsPD is warranted in patient care, as well as when comparing outcomes among radiotherapeutic techniques.