ESTRO 2020 Abstract Book

S474 ESTRO 2020

associated toxicity. Improvement is seen across both PS 0- 1 and PS 2 patient groups. The analysis supports the use of PCI for these patients; the additional survival benefit is both statistically and clinically significant given the poor prognosis of SCLC. As new treatment combinations emerge, the use of PCI for patients receiving combination chemotherapy and immunotherapy will require prospective evaluation. PO-0883 Early outcomes in patients with skull base chordomas and chondrosarcomas treated with proton therapy A. Turkaj 1 , I. Giacomelli 1 , M. Cianchetti 1 , D. Scartoni 1 , D. Amelio 1 , S. Vennarini 1 , B. Rombi 1 , F. Dionisi 1 , M. Amichetti 1 1 Centro di Protonterapia, Azienda Provinciale per i Servizi Sanitari Trento, Trento, Italy Purpose or Objective Skull base chordomas (C) and chondrosarcomas (CS) are rare, locally aggressive tumors located adjacent to critical structures. Surgery is recognized as the gold standard approach,however gross total resection is rarely possible for this reason most patients undergo subtotal resection or biopsy followed by radiotherapy.The aim of our retrospective study is to evaluate the toxicity profile and clinical outcome of patients (pts) with skull base chordomas and chondrosarcomas treated at Trento Proton Therapy. Material and Methods Between June 2015 and September 2019,36 patients with skull base C and CS were irradiated with proton therapy (PT) at our institution.Mean age was 51 years (range:10- 83).There were 32 C (89%),and 4 CS (11%).Tumors were located in clivus n= 36,right petroclival region n=1 and sellar region n=1.Median diameter at the time of treatment was 15,93 mm (range 0-51).Two lesions were only biopsied and treated with exclusive PT.Thirty four lesions had been treated with≥1 surgery;27 cases had gross residual disease at the beginning of PT;in those cases PT was performed with radical intent,8 cases were treated with adjuvant intent.Four cases were re-irradiation,3 of them after photons (total dose range 16-54 Gy) and one with carbon ions (70,4 GyRBE).Registered side effects were graded according to CTCAE4.0. Results PT was well tolerated,34 pts completed it without breaks related to acute side effects.Two pts interrupted definitively the treatment due to distal disease progression and general conditions decline.A conventional fractionation technique was used for 29 treatments, in 7 cases a Simultaneous Integrated Boost technique was used.All pts were treated with active beam scanning PT. Mean high-risk (HR) PTV volume was 59 cc(range 2.20- 329,4); mean low-risk (LR) PTV volume was 100 cc(range19,35 - 248,08). Mean prescribed total dose was 70 GyRBE (range 54-74 GyRBE) for HR PTV and 54 GyRBE (range 50-60 GyRBE) for LR PTV.Acute Grade (G)3 toxicity was experienced in 3 cases.No other ≥ G3 acute side effects were reported.Acute G2 and G1 toxicity was reported respectively in 22 and 34 cases (table 1).Late Grade 3 toxicities were recorded in 3 pts.Late G2 toxicities and late G1 toxicity was reported respectively in 6 and 19 patients (table 1).At a median follow-up of 18,95 (range 0- 50,70) months, 3 local recurrence were observed between 5.17 and 36.23 months.Of the 27 lesions treated with radical intent, 22 are locally controlled, in 2 cases there was local progression, one pt died during PT for general conditions decline,one pt had distant progression during PT, 2 pts died for the disease.Of the 8 pts treated with adjuvant intent all are free of disease

Conclusion Our data confirm that PT is an effective treatment for skull base tumors and considering the high doses delivered and the proximity of adjacent critical structures the toxicity late profile is acceptable.A longer follow-up is obviously needed to gain more robust data for late toxicity and long term disease control. PO-0884 Risk of radionecrosis in brain metastases treated with SRT and systemic therapy K. Holub 1,2,3 , G. Louvel 2 1 University of Barcelona- Hospital Clinic de Barcelona, Radiation Oncology, Barcelona, Spain ; 2 Gustave Roussy, Radiation Oncology, Villejuif- Paris, France ; 3 SEOR-CRIS Fundation Purpose or Objective The possibility to combine stereotactic radiotherapy (SRT) of brain metastases (BMs) with systemic treatment remains controversial, especially in terms of potential risk of increased toxicity. Radionecrosis (RN) is the main toxicity induced by SRS of BMs, observed in approximately 15% of BMs. Our study aimed to compare the incidence of RN in patients treated with SRT for BMs with and without concomitant systemic therapy and to evaluate factors influencing survival outcomes in patients with RN. Material and Methods From January 2012 to December 2018, SRT was administrated to 652 patients (p) with a total of 1565 BMs; 430 patients (65.9%) with 1018 of BMs (67.2% of all BMs) were treated with concomitant systemic treatment: 137 patients (21.0%) with immunotherapy (368 BMs, 23.4%), 130 patients (19.9%) with target therapy (TT) (320 BMs, 20.4%) and 163 patients (25.0%) with chemotherapy (330 BMs, 23.2%). In patients with RN, median total dose of 26.6 Gy was administrated (range 15-40Gy), with the most frequent dose schedules of 27Gy/3fr (29 BMs), 30Gy/3fr (28 BMs) and 33Gy/3 fr (23 BMs). All statistical tests were two-sided (p<0.05), Kaplan-Meier’s analysis were used to determine median overall survival (mOS), local and distant progresion free survival (SPSS v.23). Results A total of 147 BMs (9.5%) developed RN after SRS, with no statistically significant difference regarding concomitant therapy in this cohort (p=0.349). In the entire cohort treated with systemic treatment, RN was observed in 9.5%