ESTRO 2021 Abstract Book

S874

ESTRO 2021

Conclusion IDP approach enables safe dose escalation into the BTV FET-PET with a mean prescription dose of 70 Gy in 30 fractions. Prospective studies are needed to confirm whether this promising strategy may improve clinical outcomes of HGG. PO-1049 Hypofractionated stereotactic reirradiation in patients with high-grade gliomas M. López González 1 , R. Ciervide 2 , O. Hernando 3 , E. Sanchez 1 , A. Montero 1 , M. Garcia-Aranda 1 , B. Alvarez 1 , X. Chen-Zhao 1 , R. Alonso 1 , J. Valero 4 , P. Fernandez-Leton 1 , C. Rubio 1 1 HM Hospitales, Radiation Oncology, Madrid, Spain; 2 HM Hospitales, Radiation Oncology, madrid, Spain; 3 HM Hospitales , Radiation Oncology, Madrid, Spain; 4 HM Hospitalexs, Radiation Oncology, Madrid, Spain Purpose or Objective To evaluate the tolerance and efficacy of reirradiation with hypofractionated stereotactic radiotherapy (HSRT) in patients with histologic proved gliomas. Materials and Methods Patients with high-grade recurrence gliomas, were enrolled in this IRB-approved study to treat with HSRT to deliver 40 Gy at 4Gy/fraction or 30 Gy at 6Gy/fraction depending on the size and location of the tumor. All treatment decisions were based on multidisciplinary approach. Contouring was based on MRI and CT fused images. Treatment was delivered with Novalis ExacTrac image guided system which consists of a non invasive frame-based mask system that allows to perform stereotactic treatments. Treatment was planned on Iplan-net (v. 4.1) with either multiple non coplanar conformal beams or dynamic conformal arcs, with 3D conformal radiation therapy or IMRT. Novalis IGRT is based on two X-ray images that fuse bone structures with DRR reconstructed from CT simulation scan. Robotic 6D coach corrects with submillimeter accuracy translational and rotational errors before treatment. Results From July 2012 to September 2019, we treated and analyzed 41 patients with high-grade recurrence glioma. Medium age was 49.6 years. 26 patients (63%) were male and 15 female (37%). Primary tumor at diagnose was grade II glioma in 11 patients and grade III-IV in 30 patients. Median time from first RT to reirradiation was 21.10 months; 37.03 months in low grade gliomas and 19.17 months in high grade tumors. Recurrences were identified on the basis of radiographic presence of tumor progression on T1; T2 weighted MRI. The prescribed dose was 30 Gy in 5 fractions in 27 patients (66%) and 40 Gy in 10 fractions in 14 patients (44%). Median time from reirradiation to local progression was 4.6 months. All patients maintained prophylactic dexametasone for at least two weeks after the treatment completion. No patients demonstrated clinically significant acute morbidity, and all patients were able to complete the prescribed radiation dose without interruption. No patient required hospitalization or surgery for early acute or delayed toxicity. The median survival from the reirradiation was 9 months (range 2-34.4) Median Overall survival was 35.7 months (range 10.5-175.5); 88.1 months in grade II, and 29.1 in high grade. Conclusion Hypofraccionated reirradiation is feasible and well tolerated. No significant toxicity was observed.

PO-1050 11C-Methionine-PET scan for target delineation in patients treated with IMPT for CNS tumors. S. Martin Pastor 1 , F.A. Calvo Manuel 2 , A. Garcia-Consuegra 2 , J. Serrano Andreu 3 , J. Arbizu Lostao 4 , J. Gállego