ESTRO 2020 Abstract book

S512 ESTRO 2020

manual delineation of tumor on pre- and post- treatment MRIs. Final volumetric increase < 20 % was classified as local control and > 20 % as progression. Results The median baseline tumor volume treated was 3.7 cm 3 (range 0.3-18.1 cm 3 ) and the median follow up was 40 months (range 3-103 months). A local control was observed in 90.7% (146 patients), with 46.6% partial response (68 patients) and 53.4% stable disease (78 patients). Tumor progression occurred in 15 patients. Median volumetric variation after HFSRT was -13.2%. Initial tumor volume and isodose prescription was significantly higher for progressive tumor. Conclusion Volumetric response after HFSRT with 5 fractions of 5 Gy using CyberKnife® suggested an excellent local control and low toxicities. Long term data are necessary to evaluate more accurately the results for the tumoral evaluation after HFSRT. PO-0869 Assessment of results of radiosurgery for brain metastases from primary lung cancer D. Jezierska 1 , K. Adamska 1 1 Greater Poland Cancer Centre, Academic Physics, Poznan, Poland Purpose or Objective Lung cancer is the most common source of brain metastases. Radiosurgery allows a precise focal delivery of a high single radiation dose to brain metastases and results in high rates of local control. The purpose of our retrospective review was to asses results of radiosurgery for patients with brain metastases from primary NSCC with respect to prognostic factors. Material and Methods Retrospective review was performed of 83 patients with NSCC who had undergone radiosurgery in the Greater Poland Cancer Centre. In order to identify patients who benefited from radiosurgery, we evaluated local control and outcome after Linac-based radiosurgery and identified prognostic factors that may have affected survival of patients with brain metastases from NSCC. Survival was evaluated using the Kaplan-Meyer method. Prognostic factors were tested in univariate and multivariate analyses. Factors influencing survival at a significance level of p<0.05 in log-rank test were included in multivariate analysis with the backward stepwise selection Cox's regression method. Results Median overall survival in the whole group was 7.8 months from radiosurgery. Median survival times were different in different RPA classes. In RPA class I it was 13.2 months, in RPA II, 8.2 months, and in RPA III, 2.2 months. For 94% of patients symptoms improved or stabilized at the first follow-up visit and this neurological status did not change during 7.1 months. According to the univariate analysis, factors associated with improved survival included: RPA class 1 compared with RPA 2 and 3, RPA class 2 compared with RPA 3, Karnofsky performance status >70, control of the primary disease, radiosurgery performed more than once, level of haemoglobin >7 mmol/1, absence of extracranial metastases, volume of the biggest lesion in the brain <11 cm 3 . The multivariate analysis confirmed a significant influence on survival for the following factors: RPA class 1 as compared with RPA 3, Karnofsky performance status >70, absence of extracranial metastases, multiplicity of radiosurgery. Conclusion Stereotactic radiosurgery is a safe and effective treatment for patients with brain metastases . Age alone should not be a criterion for denying radiosurgery because it proved effective and safe in older patients. Selection of patients who are likely to benefit most is complex and should be based on prognostic factors. Karnofsky performance status proved to be the most important prognostic factor. In the

1 Rutgers Cancer Institute of New Jersey, Radiation Oncology, New Brunswick, USA ; 2 Mehmet Ali Aydınlar Acıbadem University, Radiation Oncology, Istanbul, Turkey ; 3 Mehmet Ali Aydınlar Acıbadem University, Radiology, Istanbul, Turkey Purpose or Objective Stereotactic radiosurgery (SRS) has become an increasingly utilized treatment option in the initial management of patients with brain metastases. While its efficacy is well documented, treatment related complications, particularly symptomatic radiation necrosis (RN), remains as an obstacle for wider implementation of this treatment modality. We examined risk factors associated with the development of symptomatic RN in patients treated with SRS for brain metastases. Material and Methods We performed a retrospective review of our institutional database to identify patients with brain metastases treated with SRS. We excluded patients who received prior SRS to the same metastatic lesion, though prior whole brain radiation (WBRT) was allowed. Both the development of new neurologic complaints requiring intervention, such as steroid therapy, bevacizumab, or surgery, and radiographic evidence of RN on serial MRI were required for the diagnosis of symptomatic RN. Dosimetry data were collected, and the Wilcoxon rank sum test was used to identify predictors of symptomatic RN. Results We identified 323 brain metastases treated with SRS in 170 patients from 2009 to 2018. The mean prescription dose was 22 Gy (range, 12-27.5 Gy) in 1 to 5 fractions. WBRT was received by 31% of the patients either before or after SRS. Thirteen patients (4%) experienced symptomatic RN after treatment of 23 (7%) lesions. After SRS, the median time to RN was 8.3 months. In patients with symptomatic RN, the median target volume, conformity index, coverage, normalization, V10 Gy, and V12 Gy was 7.6 cm 3 (range, 0.7-52.92 cm 3 ), 1.5 (range, 0.9-7.9), 97.4% (range, 91-100%), 85% (range, 63-90%), 28.9 cm 3 (range, 4.1-114.7 cm 3 ), and 24 cm 3 (range, 3.3-85.1 cm 3 ), respectively. Patients with symptomatic RN had a larger mean target volume (p<0.0001), and thus larger V100% (p<0.0001), V50% (p<0.0001), V12 Gy (p<0.0001), and V10 Gy (p=0.0002), compared to those without symptomatic RN. Single-fraction treatment (p=0.0025) and diabetes (p=0.019) were also significantly associated with symptomatic RN. Conclusion SRS is a feasible treatment option for patients with brain metastases with a low (7%) risk of symptomatic RN. We found that patients with larger tumor size, with larger plan V100%, V50%, V12 Gy, or V10 Gy, who underwent single- fraction SRS, or who had diabetes were at higher risk of symptomatic RN. Our results add to the SRS toxicity data and may help guide treatment decision-making and treatment planning. PO-0868 Volumetric evaluation after hypofractionated radiotherapy for meningioma treated by Cyberknife N. Milhade 1 1 CHRU Tours, Radiotherapy, Tours, France Purpose or Objective To quantitatively evaluate tumor volumetric responses after hypofractionated stereotactic radiation therapy (HFSRT) in patients treated for meningioma by CyberKnife® and analyzed predictive factors. Material and Methods Between 2010 and 2018, 161 patients (median age 62 years, range 32-85 years) underwent stereotactic irradiation with CyberKnife® (25 Gy in 5 fractions). Criteria for proposing radiotherapy were apparition/ worsening of symptoms or/and volumetric increase on successive MRIs. Volumetric assessment was performed by