High-dose salvage re-irradiation for recurrent/progressive adult diffuse glioma: healing or hurting?

Purpose To report survival outcomes and identify prognostic factors of salvage re-irradiation (re-RT) in recurrent/progressive glioma. Methods Medical records of patients treated with high-dose re-RT as part of multi-modality salvage therapy for recurrence/progression of adult diffuse glioma from 2010 to 2019 were analyzed retrospectively. Results A total of 111 patients developing recurrent/progressive high-grade glioma after adequate upfront treatment at initial diagnosis were included. The first course of radiotherapy (RT) had been delivered to a median dose of 59.4 Gy with an inter-quartile range (IQR) of 54-60 Gy. Median time to recurrence/progression was 4.3 years (IQR = 2.3–7.4 years) while the median time to re-RT was 4.8 years (IQR = 3.6–7.9 years). Re-RT was delivered with intensity-modulated radiation therapy (IMRT) using 1.8 Gy/fraction to a median dose of 54 Gy (IQR = 50.4–55.8 Gy) for a cumulative median equivalent dose in 2-Gy fractions (EQD2) of 104.3 Gy (IQR = 102.6–109.4 Gy). At a median follow-up of 14 months after re-RT, the 1-year Kaplan–Meier estimates of post-re-RT progression-free survival (PFS) and overall survival (OS) were 42.8 and 61.8%, respectively. Univariate analysis identified histological grade at recurrence/progression; histological subtype; disease-free interval (DFI) and time interval between both courses of RT; performance status at re-RT; dose at re-RT and cumulative EQD2; isocitrate dehydrogenase (IDH) mutation; and O 6 -methyl-guanine DNA methyl transferase (MGMT) gene promoter methylation as significant prognostic factors. Preserved performance status, longer DFI, prolonged time interval between both courses of RT, and presence of IDH mutation were associated with significantly improved PFS on multi-variate analysis. However, only performance status retained independent prognostic significance for OS on multi-variate analysis. Post-treatment changes were seen in 33 (30%) patients on follow-up imaging, with higher cumulative dose (EQD2 ≥ 104.3 Gy) being associated with increased risk of post-re-RT pseudo-progression. Conclusion This clinical audit reports encouraging survival outcomes and identifies key prognostic factors associated with high-dose salvage re-RT in recurrent/progressive glioma.