ESTRO 2023 - Abstract Book

S433

Sunday 14 May 2023

ESTRO 2023

Results The classifier indicated an ependymal tumor in 73.5%, a different tumor entity in 10.6% and non-classifiable tumors in 15.9% of cases, respectively. The most prevalent molecular classes were posterior fossa ependymoma group B (EPN-PFB, 32.9%), posterior fossa subependymoma (PF-SE, 25.9%), and supratentorial ZFTA fusion-positive ependymoma (EPN-ZFTA, 11.2%). With a median follow-up of 60.0 months, the 5- and 10-year-PFS rates were 64.5% and 41.8% for EPN-PFB, 67.4% and 45.2% for PF-SE and 60.3% and 60.3% for EPN-ZFTA. In EPN-PFB, but not in other molecular classes, gross total resection (p=0.009) and postoperative radiotherapy (p=0.007) were significantly associated with improved PFS in multivariable analysis. Histological tumor grading (WHO 2 vs. 3) was not a predictor of prognosis within molecularly defined ependymoma classes. Conclusion DNA methylation profiling improves diagnostic accuracy and risk stratification in adult intracranial ependymoma. The molecular class of PF-SE is unexpectedly prevalent among adult tumors with ependymoma histology and relapsed as frequently as EPN-PFB, despite the supposed benign nature. Gross total resection and radiotherapy may represent key factors in determining the outcome of EPN-PFB patients. MO-0553 Clinical outcome and quality of life of intracranial meningiomas treated with PBS Proton Therapy R. Krcek 1,2 , D. Leiser 1 , A. Bolsi 1 , D.C. Weber 1,3,2 1 Paul Scherrer Institute, ETH Domain, Center for Proton Therapy, Villigen, Switzerland; 2 Inselspital, Bern University Hospital, University of Bern, Department of Radiation Oncology, Bern, Switzerland; 3 University Hospital of Zürich, Department of Radiation Oncology, Zürich, Switzerland Purpose or Objective Meningiomas are one of the most common primary brain tumors, with the majority being benign. The current standard therapy for symptomatic or growing lesions includes surgery and/or radiotherapy. Proton beam therapy (PT) is characterized by its unique dose deposition pattern, with low entrance and no relevant exit dose beyond the target volume. Pencil beam scanning (PBS) PT improves conformality and Organs at risk sparing. In this retrospective study, we assess the clinical outcome including quality of life (QoL) of patients with intracranial meningioma WHO Grade 1, 2 and 3 treated with PBS PT at the Center for Proton Therapy/Paul Scherrer Institute between 1997 and 2022. Materials and Methods Two hundred patients with intracranial meningioma WHO Grade 1-3 (Median age 50.4 years, 72.5% female, 70% grade 1, 27.5% grade 2 and 2.5% grade 3) were analyzed. Acute and late side effects were classified according to CTCAE version 5.0. Time to event data (Progression Free Survival (PFS) and Overall Survival (OS)) were calculated from the first day of PT using Kaplan-Meier estimates for the whole cohort, subgroups were compared by log-rank test and multivariable Cox regression (SPSS v28). QoL was assessed descriptively by the EORTC-QLQ-C30 and BN20 questionnaires. Results The median follow-up was 65 months (range 3.8-260.8 months). Five year local PFS was 94.2% for grade 1 and 66.5% for grade 2 or higher and the OS 95.7% and 81.8% for these two grade groups, respectively (both, p<0.001). Twenty local failures have been observed; of those 15 (75%) failures have been in-field, while 5 (25%) failures were marginal. Failures occurred significantly (p<0.008) more frequent in grade 2 or 3 meningiomas (grade 1: n=7, grade 2/3: n=13)), and when PT was initiated at the timepoint of progression or recurrence as opposed to upfront therapy (multivariable, p=0.006, univariable p=0.01). We did not observed any high-grade late toxicity in a majority (n=176; 88%) of patients. Nevertheless, 24 grade 3 or higher toxicities were observed, mainly optic toxicity (grade 4 radiation-induced optic neuropathy or retinitis, n=11; grade 3 cataracts, n=4) and brain necrosis/stroke (grade 5, n=1; grade 3, n=4). No correlations of grade 3 toxicity or higher with histology and/or localization of the tumor (skull base vs. non-skull base) or sex, but a correlation with higher age (p=0.047, multivariable) was observed. QoL was assessed for 78 (39%) patients, of those 41 patients with a follow-up of at least 3 years. The result of the QoL analysis will be presented during ESTRO’s annual meeting Conclusion PBS Proton Therapy leads to a high local control in intracranial meningiomas with a low rate of high grade toxicity. Radiation-induced optic neuropathy was the most common high-grade late toxicity. As outcome was better when meningiomas were treated upfront and not in case of recurrence or tumor progression, early proton therapy should be considered for these meningioma patients. MO-0554 Validation of a NTCP model for temporal lobe radionecrosis in patients receiving proton beam therapy J. King 1 , S. Gaito 1 , A. France 2 , A. Holtzman 3 , D. Indelicato 3 , R. Colaco 1 , G. Whitfield 1 , S. Pan 1 1 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom; 2 The Christie NHS Foundation Trust, Proton Clinical Outcomes Unit, Manchester, United Kingdom; 3 UF Health Proton Therapy Institute, Radiation Oncology, Jacksonville, USA Purpose or Objective Temporal lobe radionecrosis (TRN) is a well-described side effect following high-dose proton beam therapy (PBT) to the base of skull (BoS) for radioresistant tumours, such as chordomas and chondrosarcomas. Due to their close proximity to the BoS, the temporal lobes are particularly at risk in these diagnoses, where incidence of symptomatic high-grade TRN is reported to be up to 10%. High grade TRN can have a major impact on quality of life and is sometimes life-threatening. Accurate estimation of risk is useful in the clinic for consent purposes and, whenever possible, plan optimisation. Schröder et al. developed a normal tissue complication probability (NTCP) model to quantify the risk of TRN on a structure (individual temporal lobe) or patient basis [1]. However, external validation of NTCP models is necessary to ensure their applicability in different settings. The aim of our study is the validation of this model, for its implementation into clinical practice.