Abstract Book

ESTRO 37

S368

PO-0719 Risk factors influencing survival after re-Op plus re-RT for recurrent high-grade gliomas S. Chun 1 1 SNUH, Radiation Oncology, SEOUL, Korea Republic of Purpose or Objective Despite aggressive combination of surgery, radiotherapy and chemotherapy, majority of high grade glioma patients relapse. There is no consensus on standard treatment for recurrent high grade glioma. The efficacy of adjuvant reirradiation (re-RT) after re-Op is not clearly defined. This retrospective study was to evaluate benefit and safety of re-RT after re-op. Material and Methods Total 91 patients with recurrent high grade gliomas were re-operated from 2009 to 2015. Adjuvant radiotherapy was combined as initial therapy. At recurrence and after reoperation, treatment option was discussed in multidisciplinary clinic or neuro-oncologic joint conference. Among 91 patients, 48 had re-RT but 43 had not. Results Two groups differed in age distribution and proportion of adjuvant chemotherapy, IDH-1 mutation , 9p21 homozygous deletion. Eighty-four among 91 patients (92.3%) showed progression. Median progression free survival (PFS) was 6.35 months (0.1-73). Age(<50, ≥50), WHO grade, MGMT status, IDH-1 mutation, 1p/19q codeletion, re-RT and chemotherapy were significant in univariate analysis for PFS. In multivariate analysis with factors with p value < 0.1, WHO grade, MGMT- methylation, re-RT, chemotherapy showed significant for PFS. Median overall survival (OS) was 17.6months; 12.2m with re-Op, 21.7m with re-Op plus re-RT. ( p =0.09) In multivariate analysis, age, WHO grade, MGMT methylation, IDH-1 mutation, re-RT showed significance for OS. In order to define prognostic factors and potential indication for re-RT, pretreatment factors with poor prognosis by multivariate analysis (WHO Grade IV, MGMT promoter unmethylation and age≥50) were selected. Benefit in OS or PFS with Re-RT plus re-Op over re-Op alone was definite in the subpopulation having risk factors 2 or more. In re-RT group, 4 patients (8%) had more than grade 2 toxicity, and 3 patients (6%) did not complete re-RT. Conclusion Re-RT after re-Op resulted in better PFS with tolerable level of toxicity. Survival gain was more prominent in the patient with two or more risk factors (WHO Grade IV, MGMT promoter unmethylation, age≥50). PO-0720 Single-fraction versus hypofractionated stereotactic radiosurgery for medium-sized brain metastases Y.H. Cho 1 , H. Chon 1 , K. Yoon 1 , D. Lee 1 , D. Kwon 1 1 Asan Medical Center- Univ of Ulsan, Neurosurgery, Seoul, Korea Republic of Purpose or Objective For the treatment of brain metastases (BMs), stereotactic radiosurgery (SRS) typically delivered in a single fraction is usually indicated for small tumors less than 3 cm in diameter, because the risk of radiation toxicity substantially increases as the tumor size increases thereover. Given recently suggested efficacy and safety of hypofractionated SRS in treating large-sized BMs, we investigated the clinical relevance of this approach specifically in treating medium-sized BMs of 2.5 to 3 cm compared with single-fraction SRS. Material and Methods Between 2011 and 2015, a total of 100 patients with newly diagnosed BMs (n=105) of 2.5 to 3 cm had been treated with either single-fraction SRS using the Gamma Knife (GK; n=67; median 58 years) or hypofractionated

SRS using the CyberKnife (CK; n=38; median 64 years) at our institution. Primary cancers originated from the lung (n=56, 53.3%), the breast (n=22, 21.0%), the gastrointestinal tract (n=14, 13.3%), and others (n=13, 12.4%). A median marginal dose 21 Gy (range, 18-23 Gy) was delivered for single-fraction GK and a median cumulative dose 35 Gy (range, 27-41 Gy) was delivered in median 5 daily fractions (range, 3-5 fractions) for hypofractionated CK. None of the patients received any prior or upfront whole brain radiotherapy. In each patient, treatment outcome was measured by local tumor control (LTC), overall and progression-free survival (OS and PFS), and the occurrence of radionecrosis (RN). Results With a median follow-up of 14 months (3-59 months), significant differences were observed in the incidence of RN (29.9% versus 5.3%, P=0.004) and LTC (LTC rates at 1 year 66.6% versus 92.4%, P=0.035) between the single- fraction versus hypofractionated SRS groups. There were no differences in PFS (median 6 months versus 6 months, P=0.368) and OS (median 13 months versus 18 months, P=0.234) between the groups. Conclusion These findings suggest a better safety and efficacy profile of hypofractionated SRS compared with single-fraction SRS for the treatment of medium-sized BMs. Further prospective studies are needed to address definitive conclusions. PO-0721 Multicentric experience of hypofractionated stereotactic radiotherapy for intracranial meningiomas F. Meniai-Merzouki 1 , V. Bernier-Chastagner 2 , J. Geffrelot 3 , E. Tresch 4 , T. Lacornerie 5 , E. Lartigau 1,6 , D. Pasquier 1,6 1 Centre Oscar Lambret, Academic Department of Radiation Oncology, Lille, France 2 Institut de cancérologie de Lorraine, Radiation oncology Department, Nancy, France 3 Centre François Baclesse, Radiation Oncology Radiation, Caen, France 4 Centre Oscar Lambret, Biostatistic Department, Lille, France 5 Centre Oscar Lambret, Medical Physics Department, Lille, France 6 CRISTAL- UMR CNRS 9189, Lille University, Lille, France Purpose or Objective To evaluate efficacy and tolerance of hypo-fractionated stereotactic radiation treatment (HFSRT) in the management of intracranial meningiomas in three French radiotherapy departments. Material and Methods Between December 2008 and June 2016, 126 patients with 136 intracranial meningiomas were included and treated with robotic hypo fractionated stereotactic radiotherapy. The median age was 61 years (range: 21- 92). The sex ratio was 2:1 in favor of women. HFSRT was performed as primary irradiation in 96 (76 %) patients and as re irradiation in 30 (34 %) patients. 87 patients (69%) were symptomatic before treatment. The median tumor volume was 4.84 cm3 (0.31-44.7). Tumors were located at the false in n=20 cases (15%), convexity n= 42 cases (31%), posterior cerebral fossa in 27 cases (20%), skull base in 27 (20%), optic nerves in 3 cases (2%) and parasagittal in 17 cases (12%). According to the WHO classification, meningiomas were predominantly (88%) grade I in primary HFSRT group, and, grade II (52%) and grade III (14%) in the re-irradiated patients. The median prescription dose was 25Gy (12-40) with a median number of fractions of 5 (3-10) on the 80% isodose. Endpoints were local control, toxicity and relief from symptoms. Follow-up was clinical and radiological (MRI) every 3-6 months.