ESTRO 2021 Abstract Book

S634

ESTRO 2021

Conclusion Radiation Oncology departments caring for patients with CIEDs should consider a collaborative educational approach involving leadership from nursing, RTs and electrophysiology/pacemaker evaluation clinics. Formal competency should be confirmed and documented upon hire as well as annually to support consistent and safe clinical practice. Though determining who is at greater risk for CIED damage and/or failure from the effects of radiation therapy (as well as the compatibility of newer technologies like MR-guided radiation therapy) is outside the scope of this educational intervention, it warrants further study/guideline for clinical implementation.

Poster discussions: Poster discussion 13: CNS 2

PD-0800 Radiotherapy in IDH wild-type multifocal high-grade glioma D. Fleischmann 1 , R. Schön 1 , S. Corradini 1 , R. Bodensohn 1 , I. Hadi 1 , J. Hofmaier 1 , R. Forbrig 2 , N. Thon 3 , M. Dorostkar 4 , C. Belka 1 , M. Niyazi 1 1 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany; 2 University Hospital, LMU Munich, Institute of Neuroradiology, Munich, Germany; 3 University Hospital, LMU Munich, Department of Neurosurgery, Munich, Germany; 4 Faculty of Medicine, LMU Munich, Institute of Neuropathology, Munich, Germany Purpose or Objective Radiotherapy with or without concomitant chemotherapy is the standard treatment for IDH wild-type high- grade glioma patients, but for the rare situation of multifocal spread at initial diagnosis no standard treatment is defined as of yet. To assess the safety and efficacy of radiotherapy for this severe condition, we conducted the following observational study. Materials and Methods IDH wild-type high-grade glioma patients with multifocal spread at initial diagnosis treated with conventionally fractionated radio(chemo)therapy between 04/2011 an 04/2019 were included in this retrospective observation. Radiotherapy treatment plans were analysed regarding GTV and PTV volumes, V30Gy and V45Gy of the brain and PTV to brain ratio. Risk and safety assessment of radiotherapy treatment was assessed by analysing the adverse events occurring during radiation treatment and follow-up. Assessment of efficacy was performed through Kaplan-Meier analysis of overall and progression-free survival, defined as survival from the beginning of radiation treatment until death or MRI diagnosis of disease progression. Results 20 IDH wild-type high-grade glioma patients with multifocal spread at initial diagnosis (male/female 13/7; median age 61 years, range 42-84 years) were included into the analysis. Histopathological diagnosis was performed after neurosurgical resection (n=2) or stereotactical biopsy (n=18) and revealed IDH wild-type glioblastoma in 18 cases, diffuse astrocytic glioma, IDH wild-type with molecular features of glioblastoma in one case and anaplastic astrocytoma, IDH wild-type in one case. Radiotherapy was applied with a total dose of 60 Gy in 30 fractions (n=15), 59.4 Gy in 33 fractions (n=3), 55 Gy in 25 fractions (n=1) and 50 Gy in 20 fractions (n=1). Concomitant chemotherapy regimens involved temozolomide (n=16), temozolomide/lomustine (n=1) and bevacizumab (n=1). Median volumes of the GTV and PTV were 26 cm 3 and 425.7 cm 3 . Median PTV to brain ratio was 32.8 %. Median V30Gy and V45 of the brain were 59.9 % and 40.7 %. Grade 2 toxicities as observed in 8 cases included alopecia (n=2), cushingoid symptoms (n=2), fatigue, hyperglycemia, intracranial hemorrhage, platelet count decrease (n=3), thromboembolic events (n=2) and vomiting. Grade 3 toxicities in 4 cases included cerebral edema (n=3), febrile neutropenia (n=1) and seizure (n=1). One grade 4 toxicity of white blood cell decrease as a result of concomitant chemotherapy was observed. 5 months median progression-free survival (95% CI 2.8-7.2 months) and 7 months median survival (95% KI 4.8-9.2 months) were achieved. Conclusion Despite large radiation treatment volumes, an acceptable rate of high-grade toxicities was observed in this case series of IDH wild-type multifocal high-grade glioma patients. As survival in patients with multifocal spread at initial diagnosis is still much shorter as in unifocal high-grade glioma patients, further prospective studies on multimodal treatment optimisation are warranted. PD-0801 Spatial distribution of post-radiation lesions in diffuse glioma: a voxel-wise analysis A. van der Boog 1 , S. David 1 , A. Steennis 1 , J.W. Dankbaar 2 , T. Snijders 3 , P. Robe 3 , J. Verhoeff 1 1 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands; 2 University Medical Center Utrecht, Radiology, Utrecht, The Netherlands; 3 University Medical Center Utrecht, Neurology and Neurosurgery, Utrecht, The Netherlands Purpose or Objective Radiotherapy is one of the pillars of treatment in diffuse glioma. When high-dose radiation is administered it can induce apoptosis of tumor cells and inhibit tumor growth, but it may also affect the surrounding healthy brain tissue. Post-radiation injury, including pseudoprogression and late-onset radionecrosis, is a relatively common late effect of treatment and occurs in 20-30% of the patients. Although the precise cause of these lesions remains to be elucidated, vascular damage appears to play a role. Post-radiation cellular and structural changes in cerebral vasculature with subsequent breakdown of the blood-brain barrier have been demonstrated previously. In this study, we aimed to explore the spatial distribution of post-radiation lesions and investigate a relation with both vascular and functional locations. Materials and Methods We accessed a retrospective database of 144 adult cases with WHO grade II-IV supratentorial gliomas, who received surgery and postoperative MRI within 3 days in 2012-2014. We identified 101 patients who received