ESTRO 2022 - Abstract Book

S676

Abstract book

ESTRO 2022

Fifty-two patients were included in the study: median age at RT was 5.6 (range, 0.9-30.3) years, median RT dose was 40Gy. At RIM diagnosis, median age was 33.9 (range, 13.8-54.1) years, with median latency period of 25.5 (range, 8.8- 53.2) years. 37% of patients had multifocal RIM. 88% of patients were asymptomatic at presentation. A total of 87 RIM were identified. Median follow-up was 11 years. RIM location was convexity (48%), falcine/tentorial (34%), basal (16%), and spinal (2%). Initial RIM management was active surveillance (77%), upfront surgery (21%), SRS (1%), chemotherapy (1%). Active surveillance was adopted for 67 RIM in 40 patients. Of these patients, 82.5% had RIM diagnosed on MRI screening. At 10 years, the cumulative actuarial incidence of surgery for initially surveilled RIM was 21% (95%CI, 12%-31%). The most common indication for surgery was asymptomatic tumour growth (62.5%). Neurological sequelae due to RIM progression was reported in 2 (5%) patients on active surveillance. MRI data was available for 61 (91%) RIM on active surveillance. Mean tumour volume at diagnosis was 0.53cm 3 (SD=1.14). Median absolute growth rate was 0.05cm 3 /year (IQR 0.01-0.11); median relative growth rate was 26% per year (IQR 7-79). Radiological growth pattern of individual RIM is shown in Figure 1. Resection was performed for 33 RIM (30 patients), 54.5% at diagnosis and 45.5% after active surveillance. Pathological grade was WHO Grade I (85.2%), II (11.1%), III (3.7%). Gross total resection was achieved in 79%. Following resection, actuarial 10-year local recurrence rate was 12% (95%CI: 3-29).

There were 8 deaths: 1 due to RIM. OS was 88% (95%CI, 74%-95%) at 10 years.

Conclusion Active surveillance is a safe initial strategy for small, asymptomatic RIM, with low rates of neurological morbidity. Asymptomatic RIM typically demonstrate slow radiological growth. However, long-term MRI surveillance for asymptomatic RIM is required, as 21% of patients will require surgical intervention within 10 years, most commonly for asymptomatic tumour growth.

OC-0761 Reirradiation of pediatric patients with diffuse midline glioma

D. Østergaard 1 , I.R. Vogelius 2 , R. Mathiasen 3 , K. Nysom 4 , M. Jørgensen 1 , A.M. Sehested 4 , M. Maraldo 1

1 Rigshospitalet, Section of Radiotherapy, Department of Oncology, Copenhagen, Denmark; 2 Rigshospitalet/ Copenhagen University, Section of Radiotherapy, Department of Oncology/2Faculty of Health and Medical Sciences, Copenhagen, Denmark; 3 Rigshospitalet, Department of Pediatrics and Adolescent Medicine, Copenhagen, Denmark; 4 Rigshospitalet, 3Department of Pediatrics and Adolescent Medicine, Copenhagen, Denmark Purpose or Objective 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