ESTRO 2021 Abstract Book

S956

ESTRO 2021

Results 60 patients were included, with a median age of 61.5 (31-84) years. The majority had adenocarcinoma (85.0%), stage cTx/1 (57.6%), cN0 (61.7%), and received adjuvant ChT (83.3%). The most used ChT regimen was Cisplatin with Vinorelbine (53.5%). 13.3% underwent neoadjuvant ChT only. Most patients underwent lobectomy (78.3%) and were staged as (y)pT2 (51.7%). 5.0% of patients initially staged as cN2 showed a complete pathological nodal response (ypN0). From the study of the surgical specimen, 55.9% had at least one N2 lymph node involved, 23.7% two nodes and 20.3% at least three. The most widely used RT fractionation was 50 Gy in 25 (48.3%) and 28 (16.7%) fractions, the majority (58.3%) using VMAT technique. The analysis of DFS, R-DFS and OS was performed with a median follow-up time of 27.2, 38.9 and 40.0 months, respectively. The 3 years DFS, R-DFS and OS were 45.8%, 89.1% and 76.6%, respectively. The median DFS was 28.1 months. In the univariate analysis, cN2 stage patients (HR = 2.120; 95% CI: 1.059-4.245) and patients with 3 or more metastatic N2 nodes (HR = 2.735; 95% CI: 1.183-6.324) had significantly lower DFS compared to patients cN0-1 and with less than two N2 nodes involved, respectively. In the multivariate analysis, only the presence of 3 or more metastatic N2 nodes (HR = 2.564; 95% CI: 1.105-5.948) maintained statistical significance in reducing the DFS, which was also shown to have a negative impact on OS (HR = 6.386; 95% IC: 2.497-16.333). None of the evaluated factors showed an association with R-DFS. Conclusion The presence of ≥3 metastatic N2 nodes is associated with lower DFS and OS rates than less N2 involvement. In this sample, we observed median and 3-year DFS rates in agreement with the data recently published of the LungART study. PO-1149 SBRT for lung cancer: outcomes from biopsy-proven and empirically treated lung lesions L. Guzmán Gómez 1 , J. Luna Tirado 2 , D. Gonsalves Pieretti 3 , M. Montero Feijoo 2 , M. Rincón Pérez 2 , I. Azinovic Gamo 2 1 Fundación Jiménez Díaz University Hospital, Radiation Oncology , Madrid, Spain; 2 Fundación Jiménez Díaz University Hospital, Radiation Oncology, Madrid, Spain; 3 GenesisCare, Radiation Oncology, Toledo, Spain Purpose or Objective To compare outcomes in patients treated with lung stereotactic body radiotherapy (SBRT) for early stage medically inoperable non-small-cell lung cancer, both biopsy-proven and empirically managed. Materials and Methods We identified 97 patients treated with lung SBRT for all indications between January 2015 and June 2018. Patients with confirmed or obvious metastatic disease were excluded. Fifty-one patients met eligibility criteria for this study: 21 patients (41%) were treated without biopsy while 30 patients (59%) were treated with pathological confirmation of NSCLC. Each patient had appropriate pretreatment staging with CT scans and FDG-18 PET-CT. A 4D CT for treatment planning simulation to account for respiratory motion was performed. Dose-prescription ranged from 50 to 60 Gy in 5 - 8 fractions (table 1) . Treatment was delivered on Elekta Beam Modulator™ linear accelerator, using volumetric modulated arc therapy (VMAT) with 6-10 MV photon beam energy. Image guidance (IGRT) was performed by means of CBCT acquisitions prior to each treatment. After treatment, patients were followed with CTs or PET/CTs at least every 3 months for 1 year and every 4–6 months thereafter. The primary end points were local control (LC), overall survival (OS) and treatment-related toxicity. Response to treatment and local/distant control was assessed via RECIST criteria. Results Median age at treatment was 70 years (range, 60-89 years). 65% were men. 78% of patients had some degree of chronic obstructive pulmonary disease and 65% had an extensive smoking history. Empirically treated patients had smaller tumors (median size 15mm) than those with biopsy proven lesions (median size 22mm). Median follow up for patients with pathologically proven NSCLC was 18 months and 17 months for those without biopsy. LC and OS did not differ between the groups with 2-year local control of 95 % and 94% for empiric treatment and biopsy proven, respectively; and 2-year OS of 82 and 84%, respectively. Regional and distant control were likewise similar, with rates at 2 years of 90 and 89% for clinical diagnosis and pathologic diagnosis, respectively, for regional control. Distant control rates were 84 and 86% at 2 years for the empiric group and biopsy proven group, respectively. SBRT was very well tolerated in both groups of patients, with no acute or late ≥ grade 3 toxicity. Three patients in the biopsy proven group developed grade 1 asthenia at the end of treatment, 2 patients grade 1 rib pain correlating to SBRT location and 1 patient grade 2 pneumonitis. In the empirically treated group, 2 patients also developed grade 1 asthenia. Conclusion SBRT is a safe and effective treatment for patients with non-small-cell lung cancer, with comparable results in empirically treated patients. PO-1150 Prognostic role of [18F]FDG PET-CT after induction chemotherapy for locally advanced Non Small Lung Cancer A. Masarykova 1 , D. Scepanovic 1 , P. Povinec 2 1 National Cancer Institute of Slovakia, Radiation Oncology, Bratislava, Slovakia; 2 BIONT , PET Center, Bratislava, Slovakia