ESTRO 38 Abstract book

S743 ESTRO 38

Conclusion The dose distribution and dosimetric parameters of both the CyberKnife and VMAT plans are clinically acceptable lung treatment requirements. While the CyberKnife may deliver less lung dose than linac‐based systems for tumors close to the anterior chest wall. Although there are some differences in dosimetric analysis, it is likely that robotic radiosurgery and volumetric modulated arc therapy plans would be clinically indistinguishable. EP-1360 Salvage SBRT for postoperative recurrence of NSCLC S. Aoki 1 , H. Yamashita 1 , W. Takahashi 1 , K. Nawa 1 , T. Ota 1 , Y. Nozawa 1 , S. Ozaki 1 , T. Nakamoto 1 , K. Nakagawa 1 1 University of Tokyo Hospital, Radiology, Tokyo, Japan Purpose or Objective Standard treatment for patients with early-stage non- small cell lung cancer (NSCLC) who undergo surgery and subsequently develop local failure or intrathoracic oligo- recurrence remains controversial. We aimed to assess the feasibility of stereotactic body radiotherapy (SBRT) for these patients. We also evaluated factors associated with indicies of survival. Material and Methods Patients treated with SBRT for NSCLC recurrence who previously underwent curative surgical resection from October 2011 to October 2016 were evaluated. Post- recurrence survival and toxicity were analyzed, and prognostic factors for overall survival (OS), progression free survival (PFS) after salvage SBRT were identified by univariate and multivariate analysis. Results A total of 51 patients and 58 tumors were analyzed. Median follow-up time was 25 months (35 months for surviving patients), and median OS after salvage SBRT was 32 months. The 1- and 3-year OS, PFS rate was 82.4% and 59%, 82.4% and 59%, respectively. Only 4 patients (7.8%) developed local failure. Median local control rate (LCR) was 71 months and the 1- and 3-year LCR was 97.8% and 94.9%. Four patients experienced grade≤3 radiation pneumonitis and one experienced grade 5. Gender, location, type of surgery (lobectomy or limited suegery), and operability of recurrent tumors were independent prognostic factors for OS. Conclusion This study suggested that salvage SBRT is effective and well-tolerated in recurrent NSCLC patients with postoperative locoregional recurrence. EP-1361 Survival after two schedules of SBRT to centrally located lung tumors M. Jelin 1 , C. Kristiansen 1 , S.S. Jeppesen 1,2 , M. Nielsen 3 , O. Hansen 1,2,4 1 Odense University Hospital, Dept. Oncology, Odense, Denmark ; 2 Odense University Hospital, AgeCare. Academy of Geriatric Cancer Research, Odense, Denmark ; 3 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark ; 4 University of Southern Denmark, Institute of Clinical Research, Odense, Denmark Purpose or Objective It is a challenge to apply stereotactic radiotherapy (SBRT) to centrally located non-small cell lung cancer (NSCLC). Initially we used 80 Gy/8F (BED10= 160 Gy), but changed the schedule to 50 Gy/5F (BED10=100 Gy). We here report the survival data for patients who were treated with either All patients have been prospectively registered. Additional data have been obtained retrospectively from patients files. Included patients were patients treated initially with one of the two schedules. Patients treated for recurrent disease, and patients treated in combination with of the two schedules. Material and Methods

Results Thirty-three patients with 36 lesions were eligible and included in this study. The median follow-up time was 32 months. Estimated incidences of LR and DM were 37.62% and 15.92%, respectively, at 1 year and 48.02% and 21.23%, respectively, at 2 years. The progression-free survival and overall survival of all patients were 62.40% and 90.30%, respectively, at 1 year and 52.00% and 69.90%, respectively, at 2 years (Figure 1). Twenty-six patients experienced grade 1 SBRT-related toxicity, 11 patients experienced grade 2 SBRT-related toxicity, and 3 patients experienced grade 3 toxicity. There were no grade 4/5 toxicities or SBRT-related deaths during the follow-up period (Table 1). Conclusion SBRT appears to be a safe and potentially effective alternative therapeutic option for de novo pulmonary tumors following early-stage NSCLC radical resection, despite impaired pulmonary reserve. EP-1359 DosimetricAppraisa ofVMATforStereotacticRadiosurgery inLungLesionsinComparisontoRobotic Radiosurgery E. Erdogan 1 , P. Boydak 1 , B. Eren 1 , F. Aksaray 1 1 Okmeydani Training and Research Hospital, Radiation Oncology, istanbul, Turkey Purpose or Objective Role of stereotactic radiosurgery in the treatment of lung tumors has been well defined. Stereotactic radiosurgery techniques improvements are developing everyday. Comparisons of dosimetric quality has always been an ongoing subject of new conducting clinical trials. The aim of this study is to compare the dosimetric characteristics of robotic and conventional linac‐based SBRT techniques for lung cancer. Material and Methods Ten patients with lung patients were replanned with MONACO treatment planning system (ELEKTA Infinity Linac) which use MONTECARLO algorithm. Plans were created using 2 half arcs VMAT with CyberKnife (which use MONTECARLO algorithm) and dosimetric indices compared for both treatment platform. Identical image and contour sets were used for both modalities. Dose for organ at risk for SpinalCord,Osofagus,R-L Lung for 1000cc,heart. PTVmax, treatment time, conformity index (CI), homogeneity index (HI), number of monitor units (MU). CI calculated for both platform manually as a ratio of total volume covered by reference isodose and the target volume (CI= VRI/TV). D2-D98/D50 formula used for calculation HI (ICRU 62 raports) Statistical calculations were made by SPSS Statistics 22. The Shapiro–Wilk test used for normality in frequentist statistics.Paired sample t-test and Wilcoxon signed-rank test were used for normally and not normally distributed dependent samples. Differences were considered statistically significant if p values were < 0.05. Results Robotic radiosurgery technique can achieve high degree of conformity (median CI=1.41) surrounding the inhomogeneous dose distribution (median HI= 0.27) at the cost of treatment time (mean 53 minutes). Volumetric modulated arc therapy technique improved this inhomogeneity (median HI= 0.05) and treatment time (estimated between 5 and 9 minutes) at the cost of conformity (median CI= 0,95). The number of MU necessary to deliver the prescribed dose was significantly greater in the case of CyberKnife system (p< 0.01). The dose to 1000 cc lung was well below institutional constraints for both modalities. Steep dose gradient near target volume were significantly better at CyberKnife system for all isodose volumes (80%, 60% and 40% isodose volumes) (p< 0.01)