Session Item

Diffuse midline glioma (DMG) is a primary brain tumor seen mainly in children. Following radiotherapy, the only well-documented life-prolonging therapy, the median survival is still only 11 months from diagnosis of DMG. Over the last decade, re-irradiation (reRT) at relapse has been increasingly used, showing a longer survival and symptom palliation with limited toxicity. ReRT of DMG at relapse is, however, not yet consistently considered standard of care throughout Europe. We reviewed our institution’s experience with reRT of DMG including the site of relapse and the cumulated dose to organs at risk (OAR).  

We reviewed the baseline and treatment characteristics of all patients with DMG receiving reRT from June 2011 to June 2021. Information was obtained through national electronic health records following ethical permission. For each patient, the initial and re-irradiation RT plans were visually assessed to evaluate any possible overlap between the two treatments. The cumulative dose to OAR were calculated as EQD₂ = D((d + α/β)/(2 + α/β)), with α/β=2Gy for neurological tissue based on the published literature. Records were scanned for early toxicities 6 weeks following start of reRT. 

Among 19 children from East Denmark irradiated for DMG, seven received reRT (Table 1). Their median age at diagnosis was six years (range, 2-13) and their median overall survival was 20 months (9-30). The median time from initial RT to reRT was 10 months (8-17) and the median time from reRT to death was 4 months (3-10). For six patients, the relapse overlapped with the localization of the primary tumor (Figure 1) and the cumulated doses to surrounding tissue was calculated. The median cumulated dose to the chiasm was 64 Gy (range, 37-85.), to the left and right optic nerve 20 Gy (10-24) and 23 Gy (11-33), respectively, and to left and right hippocampi 53 Gy (37-87 ) and 53 Gy (37-86), respectively. All but one patient (missing data) had improved or stabilized symptoms from both courses of RT. Early toxicities following reRT were described as minor, only managed with basic supportive care and, for two patients, no toxicity was reported at all. No patients were diagnosed with clinically significant radionecrosis.

Our data support reRT as a relevant palliative treatment for children with DMG. Despite the overlap of treatment fields, there was no reported excessive early toxicity. Due to the limited survival time of patients, palliation with minimal toxicity and high quality of life should be considered standard of care. Further studies are needed to define the optimal population for reRT of DMG.