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significantly better LC, MFS and CSS; p=0.05, = 0.058 and =0.05, respectively). Acute toxicity was very low, with 2,5% of RTOG > grade 3 pneumonitis.

Conclusion 4D-image guided SBRT with small margin ITV-PTV provided good LC and survival rates with negligible toxicity. Interestingly, patients older than 78 had significantly better outcomes. EP-1388 The role of emphysema on lung toxicity and the feasibility of a “functional treatment plan” M. Maddalo 1 , G. Benecchi 1 , I. Moschini 2 , C. Grondelli 1 , R. Rossi 1 , E. Calabri 1 , F. Salaroli 3 , M. Manicone 3 , S. Andreani 3 , F. Ghetti 3 , S. Gianni 3 , R. Rossi 3 , S. Nurmahomed 3 , G. Ceccon 3 , P. Losardo 3 , C. Dell'Anna 3 , M. Bergamini 3 , C. Ghetti 1 , N. D'Abbiero 3 1 Azienda Ospedaliero Universitaria di Parma, Medical Physics Unit, Parma, Italy 2 Azienda AUSL Piacenza, Radiotherapy, Parma, Italy 3 Azienda Ospedaliero Universitaria di Parma, Radiotherapy, Parma, Italy Purpose or Objective Although the relationship between pulmonary emphysema (PE) and pneumonitis after radiotherapy has been investigated in recent years, it still remain controversial. The aim of this study was to retrospectively examine the role of PE on radiation- induced lung toxicity (RILT). The feasibility of a “functional treatment plan (FTP)”, designed to spare the functional volumes of the lungs (FLV), was also investigated. Material and Methods 34 patients with NSCLC who underwent radiotherapy has been retrospectively selected for this study. An expert radiologist analysed the first CT after-treatment and subdivided patients in two categories: RILT-1, 13 patients with no/low RILT; RILT-2, 21 patients with high RILT. Thresholds were applied on planning CT (before- treatment) to define PE (below -900 HU) and FLV (between -899 and -500 HU). Through the Mann-Whitney test, RILT-1 and RILT-2 were compared in terms of PE volumes and of dosimetric parameters V 5Gy and V 20Gy of both total (DP TL ) and functional lungs (DP FL ). For patients who had considerable PE volumes, FTPs were developed based on VMAT technique. To selectively spare the FLV, arc sectors which involved parts of FLV were avoided and high-weight constraints for FLV were applied in the VMAT Optimizer. Results PE volume was significantly higher in RILT-1 than in RILT- 2 (p<0.05). RILT-1 was characterised by significantly lower DP TL than RILT-2 and the difference become stronger when considering DP FL . The 66.7% of FTPs were not feasible because PE was irregularly distributed over the whole lungs volume. Regarding the remaining 33.3% of the FTPs, FLV D mean averagely decreased by 0.67Gy (0.25<ΔD mean <1.52Gy).

Conclusion This study suggested that patients with emphysema were less subject to RILT. In addition, RILT was better associated with FLV exposure than total lung exposure. Therefore a FTP would be desirable, but it’s limited to a small number of cases depending on PE amount and distribution. EP-1389 Reduction of lung dose during stereotactic radiation of lung tumors using respiratory gating A. Hofmeister 1,2 , M.N. Duma 1,3 , M. Wiegandt 1,2 , S.E. Combs 1,3 , J.J. Wilkens 1,3 , M. Oechsner 1 1 Klinikum rechts der Isar - Technische Universität München, Klinik und Poliklinik für RadioOnkologie und Strahlentherapie, München, Germany 2 Technische Universität München, Fakultät für Medizin, München, Germany 3 Helmholtz Zentrum München, Institut für Innovative Radiotherapie iRT, München, Germany Purpose or Objective Stereotacic body radiotherapy (SBRT) is a well- established treatment option for lung cancer. Respiratory gating (RG) enables dose reduction to organs at risk (OARs). In this study, the possible dose reduction of the lung, thoracic wall and heart during lung SBRT, employing RG during inspiration and expiration was examined. Additionally, factors that influence the dose reduction were determined. Material and Methods 49 lung SBRT patients were retrospectively selected. All patients underwent 4D-CT scanning, consisting of 10 phase CTs representing the breathing cycle. Three radiation windows were determined per patient: Free breathing (all 10 phases), inspiration (phases 90%, 0%, 10%), and expiration (phases 40%, 50%, 60%). The gross tumor volume (GTV) was contoured in all 4DCT phases. Internal target volumes (ITVs) were determined for all three radiation windows by combining the GTVs of each respective phase. PTVs were generated by adding a 5 mm safety margin. Volumetric modulated arc therapy (VMAT) plans were calculated using prescription doses of 3x15Gy (PTV<65.5ccm) or 5x8Gy (PTV>65.5ccm) surrounding 98% of the PTV. Doses to the lung and the heart were examined. PTV volumes and 3D movements of the tumors were determined as well. Statistical analysis were performed using the Wilcoxon-Test and Spearman´s correlation coefficient. Results The results are listed in Table 1 including the median (min-max). The lung dose for Dmean and V20 is significantly higher in free breathing than with respiratory gating in inspiration and expiration (p<0.01). The lung dose is slightly lower in inspiration than in expiration, however, not significantly (p>0.05). The mean heart dose was significantly lower in expiration than in free breathing and inspiration for tumors located cranial of the heart; for those located caudal it was lower in inspiration. The correlation coefficients between the difference of the PTV-volumes (Δvolume) and the dose change (Δdose),