ESTRO 2022 - Abstract Book

S958

Abstract book

ESTRO 2022

4.83, 95%CI0.83-27.88, p=0.01) and PTV >200cc (HR:2.14, 95%CI: 0.01-9.87, p=0.02) were significant negative prognostic factors for survival. Six significant variables in univariate analysis (mass effect, multifocal tumor, surgery, resection, MGMT status and PTV) were entered into multivariable model. As a result, multifocal tumor (p=0.05), incomplete resection (p=0.01), MGMT unmethylation (p=0.03) and PTV >200cc (HR:1.99, 95%CI: 0.26-5.37, p = 0.05) were significant negative prognostic factors for disease progression. Conclusion SIB-hypoRT associated with TMZ in poor prognosis patients affected by GBM is an effective and safe treatment. Prospective study could be warranted.

PO-1127 The STEREOBRAIN trial: a case-control study of SRS vs WBRT in 4-10 brain metastases

R. Bodensohn 1 , A. Kaempfel 2 , A. Boulesteix 3 , R. Forbrig 4 , S. Garny 1 , S. Corradini 1 , C. Belka 1 , M. Niyazi 1

1 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany; 2 University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany; 3 University of Munich, Institute for Medical Information Processing, Biometry and Epidemiology, Munich, Germany; 4 University Hospital, LMU Munich, Institute of Neuroradiology, Munich, Germany Purpose or Objective At our department, whole brain radiotherapy (WBRT) has been the treatment of choice in 4-10 brain metastases until 2017. This paradigm was entirely changed to include patients within the STEREOBRAIN trial (ID: DRKS00014694). We designed this prospective single arm trial to systematically introduce stereotactic radiosurgery (SRS) to 4 to 10 brain metastases comparing this new treatment regimen with the former approach. We aimed at showing a survival benefit of this novel treatment paradigm. Materials and Methods Inclusion criteria were 4-10 brain metastases, largest diameter 2.5 cm, all histologies except SCLC, germ cell tumors, lymphoma, and ECOG ≤ 2. The retrospective WBRT cohort was identically selected from consecutive patients from 2012 to 2017 in a 1:2 fashion. At a significance level of 5%, a total number of 99 events (deaths) across the two groups allows to detect an increase in median OS from 6 months (retrospective WBRT cohort) to 11 months (SRS) considered clinically relevant (and corresponding to a hazard ratio of 0.55 assuming exponential distributions of survival times within groups) with a power of 80%. Propensity-score matching is planned to take confounders into account given the inherent bias caused by different treatment periods. Secondary endpoints were intracranial PFS and toxicity. Multiple brain mets SRS was performed using a single-isocenter technique. Results Patients were recruited from 2017 – 2020 and end of F/U was July 1 st 2021. Forty patients were recruited to the SRS cohort and 70 patients were eligible within the WBRT cohort (81 events altogether).

Conclusion Respective results from the full analysis dataset will be presented and discussed at the ESTRO 2022.

PO-1128 Radiosurgery with Cyberknife® for arteriovenous malformations: technical and dosimetrical analysis

E. Scipilliti 1 , V. Borzillo 1 , R. Di Franco 1 , F. Savino 2 , G. Leone 3 , M. Muto 3 , P. Muto 4

1 Istituto Nazionale Tumori IRCSS Fondazione G. Pascale, Radiation Oncology Unit, Napoli, Italy; 2 LB Servizi per le aziende SRL, Medical physics, Roma, Italy; 3 A.O.R.N. Cardarelli, Department of Neuroradiology, Napoli, Italy; 4 Istituto Nazionale Tumori Fondazione G. Pascale, Radiation Oncology Unit, Napoli, Italy Purpose or Objective Radiosurgery (SRS) obtain a successful obliteration of arteriovenous malformations (AVMs). Radiation injury to the vascular endothelium induced the proliferation of smooth-muscle cells and the elaboration of extracellular collagen, which leads to progressive stenosis and obliteration of the AVM nidus thereby eliminating the risk of hemorrhage. The advantages of SRS, compared to microsurgical and endovascular treatments, are that it is noninvasive, has minimal risk of acute complications, and is performed as an outpatient procedure. The primary disadvantage of SRS is that cure is not immediate; thrombosis of the lesion is achieved in most cases, but it does not occur until 2-3 years after treatment. SRS has been shown to be less effective for lesions over 10 cc in volume. Aim of the study is to describe a monoistitutional series of AVMs pts treated with CyberKnife® system (CK) in collaboration with dedicated neuroradiologist Materials and Methods All pts performed angiography, CT-angio and MR-angio and were evaluated by an expert neuroradiologist before CK treatment. All imaging data were accurately co-registered in the CK-TPS and used for target contouring delineation. The delineation of AVM targets was as follows: AVM with prior embolization targets included nidus, embolization areas and some small draining veins; for pts without embolization, the target was nidus. All pts received a single fraction of radiation. The PTV was equal to GTV. Follow-up was performed with MR-angio after 2-3 months and angiography 1 year after the treatment

Results