ESTRO 2021 Abstract Book

S866

ESTRO 2021

established. In this retrospective study we compared adjuvant radiotherapy alone with radiotherapy plus TMZ pediatric population (< 14 years). Variation in treatment was as a result of two different treatment philosophies prevalent within consultants in department at that time. Materials and Methods Between 2015 to 2017, 36 patients of pGBM were identified from our database of which 27 were included in this retrospective analysis (patients who failed to complete radiation or lost to follow up were not included). 11 patients received RT alone(40.7%)(Group A) and 16 patients (59.2%) received RT with concurrent plus adjuvant TMZ(Group B). Adjuvant therapy included conformal radiation 60 gray (or equivalent) concurrent TMZ 75 mg/m2 followed by six cycles of adjuvant TMZ 150-200 mg/m2 (day 1-5) every 4 weeks. Kaplan-Meier estimates of overall survival (OS) were determined. Univariate analysis with log-rank test was used to determine the impact of prognostic variables on survival. Results Median age at presentation was 7 years (IQR: 6-11 years) and M:F ratio was 20:7. Median tumor size for entire cohort was 4.7cms (IQR 3.4-5.5) the difference in two groups was not significant .All patients underwent maximal safe surgical resection; 16 gross total resection and 11 sub-total resection. For the entire cohort median follow up was 46.3 months, Grade 2 and above haematological toxicities were seen in 1(9%)in Group A arm vs 5(31.2%) in Group B arm (p=0.001) . Grade 2 and more nausea was seen in 2(18%) in Group A arm and 6(37.5%) in Group B arm (p=0.01).Median survival was 8.3 months in Group A arm , when compared to 9.8 months in Group B arm (p = 0.01) .

Conclusion This retrospective analysis shows advantage of concurrent and adjuvant TMZ for pGBM patients leading to superior OS in this group of patients with tolerable toxicities. The results however need to be validated in adequately powered prospective randomised study. PO-1039 Stereotactic radiotherapy with single-isocenter in multiple brain metastases P. Matteucci 1 , S. Silipigni 1 , C.G. Rinaldi 1 , I. Ridolfi 1 , P. Falco 1 , M. Fiore 1 , E. Ippolito 2 , S. Ramella 1 1 Campus Bio Medico Rome, Radiation Oncologist, Rome, Italy; 2 Campus bio Medico Rome, Radiation Oncologist, Rome, Italy Purpose or Objective An obstacle of stereotactic radiotherapy (SR) in the management of multiple brain metastases is the longer treatment time using traditional radiotherapy. Single-isocenter multitarget (SIMT) SR is a novel technique that permits rapid therapy delivery to multiple metastases. Materials and Methods We identified patients with advanced solid tumors with multiple brain metastases treated with SR in 3 fractions using SIMT technique at our institution. To evaluate radiological response according to RANO criteria a three-month control MRI was performed after each treatment Results 13 patients with 71 brain metastases were treated at our institution between December 2018 and June 2020 (primaries: 69.2% Non Small Cell Lung Cancer -NSCLC, 7.7% melanoma, 7.7% Merkel cancer and 15.4% breast cancer). Only 2 patients received whole brain radiotherapy (WBRT) before SIMT. The other 11 patients performed only SR with single isocenter on multiple metastases for a maximum of 5 lesions treated simultaneously. The prescription dose was 9 Gy for fraction with prescription to isodose of 80% to the isocenter. Lower doses were considered in case of organs at risk close to target or in case of previous treatment, however metastases number didn't influence the prescribed dose. All patients performed simultaneously systemic therapy. Response at three months MRI was: 2 (15.4%) had brain progression, 5 (38.5%) stable disease and 6 (46.2%) partial response. With a median follow-up of 12 months (range 3-20 months), only 2 asymptomatic radionecrosis were detected in patients treated previously with WBRT.