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distant metastases free survival. PD1 and PD-L1 positivity also correlated with a high infiltration with CD3/CD8-cytotoxic lymphocytes (p<0.001). Lymphocytic infiltration as well as PD1 and PD-L1 expression was significantly more common in oropharyngeal carcinomas (p=0.001) and HPV-DNA/p16-positive tumors (p<0.001). Furthermore, high tumor infiltration of CD56+ natural killer cells correlated with significantly improved overall survival in the postoperatively treated cohort The immune infiltration of head and neck tumors displays a strong prognosticator for response to CRT regardless of the treatment setting. Our unicentric results could be validated in a multicentric DKTK cohort. Prospective trials (e.g. the already recruiting DKTK-ROG trial) will further evaluate the role of the immune microenvironment in SCCHN. OC-0325 Sequential VMAT planning of 68GaPSMA-PET and PSA guided radiotherapy of lymph nodes and prostate bed V. Johannesson 1 , E. Wieslander 1 , E. Kjellen 1 , E. Brun 1 , U. Bitzen 2 , T. Olsson 1 , P. Höglund 3 , P. Nilsson 1 , A. Gunnlaugsson 1 1 Skåne University Hospital, Hematology- Oncology and Radiation Physics, Lund, Sweden 2 Skåne University Hospital, Clinical Physiology and Nuclear Medicine, Lund, Sweden 3 Skåne University Hospital, Medical Statistics and Epidemiology, Lund, Sweden Purpose or Objective PROPER is a prospective phase II study where patients with rising PSA after prostatectomy are treated with 68 Ga-PSMA-PET guided salvage radiotherapy. PSA response during treatment is used to select patients for further irradiation of lymph nodes in case of non-response. This demands sequential irradiation of the prostate bed and pelvic lymph nodes. The aim of this work is to describe and evaluate the sequential composite volumetric-arc therapy (VMAT) planning of patients selected for nodal irradiation. Material and Methods All patients included in the PROPER study (open-label, phase II trial, NCT02699424) received initially 50 Gy (25x2.00 Gy) to the prostate bed and were thereafter classified as either responders (PSA resp@5w ) or non- responders (PSA non-resp@5w ) depending on the PSA value after the fifth week of radiotherapy. Responders were treated as planned with additional 20 Gy (10x2.00 Gy) to the prostate bed and the non-responders with additional 20 Gy to prostate bed and 50 Gy (25x2.00 Gy) to the lymph nodes. The latter treatment was delivered with a sequential VMAT plan using the initial prostate treatment plan as a base (Base Dose Plan, Eclipse version 13.6). Furthermore, 68 Ga-PSMA-PET positive pelvic lesions were treated with a SIB technique. In this study we chose to use physical dose constraints. We analyzed the dose distributions for non-responders (a sum of three plans for each patient) and compared them with the dose-volume constraints. Furthermore we also present these parameters corrected for fractionation effects using biologically equivalent doses at 2 Gy/fraction with α/β=3 Gy (EQD2 3 ). Results To date 44 patients have been included in the trial. So far 26 have been classified as non-responders, all receiving additional irradiation to the pelvic lymph nodes and those with 68 Ga-PSMA-PET positive lesions received an additional boost. A summary of the main dose-volume parameters is as follows: PTVT (constraints: D 98% >65.5Gy): D 98% phys_mean = 69.3Gy (range: 67.7-70.0), D 98%_EQD2_mean 68.2Gy (66.1-69.1). PTVN (constraints: D 98% >46.5 Gy): D 98% phys_mean 48.0Gy (47.1 – 49.0), D 98% EQD2_mean 43.0Gy (41.3- (p<0.0001). Conclusion

44.6). The doses to OAR were as follows: rectum (constraints V 70Gy <20%): V 70Gy_mean :19.5% (8-31), V 70GyEQD2_mean 16.3% (2.0 – 16.0) and Bowel bag (-PTV) (V 45Gy < 195cc): 57cc (8-153) (phys.), 25cc (3.6-119.3) (EQD2 3 ). Conclusion This is to our knowledge the only study presented on sequential VMAT radiotherapy using Base Dose Plan technique in the pelvis. Our results show that it can be delivered with adequate dose-coverage to the prostate bed (both physical and biologically converted doses), with acceptable doses to OAR and dose coverage of lymph nodes regarding physical dose. The EQD2 3 corrected near minimum doses (D98%) to lymph nodes were somewhat low to avoid warm intersections between plans. The clinical outcome of this study will confirm the feasibility of this technique. Further development will be performed to improve the EQD2 3 coverage of the pelvic nodes as well. OC-0326 QOL After APBI (Multicatheter Brachytherapy) Versus WBI: 5-Year Results, Phase 3 GEC-ESTRO Trial R. Schäfer 1 , V. Strnad 2 , C. Polgár 3 , W. Uter 4 , G. Hildebrandt 5 , O.J. Ott 2 , D. Kauer-Dorner 6 , H. Knauerhase 5 , T. Major 3 , J. Lyczek 7 , J.L. Guinot 8 , J. Dunst 9 , C. Gutierrez Miguelez 10 , P. Slampa 11 , M. Allgäuer 12 , K. Lössl 13 , G. Kovacs 14 , R. Fietkau 2 , A. Resch 6 , A. Kulik 7 , L. Arribas 8 , P. Niehoff 15 , F. Guedea 10 , C. Gall 4 , B. Polat 1 1 University Hospital Würzburg, Department of Radiation Oncology, Würzburg, Germany 2 University Hospital Erlangen, Department of Radiation Oncology, Erlangen, Germany 3 National Institute of Oncology, Center of Radiotherapy, Budapest, Hungary 4 University Erlangen-Nuremberg, Department of Medical Informatics- Biometry and Epidemiology, Erlangen, Germany 5 University Hospital Rostock, Department of Radiation Oncology, Rostock, Germany 6 University Hospital AKH Wien, Department of Radiation Oncology, Vienna, Austria 7 Centrum Onkologii - Instytut im Marii Sklodowskiej, Brachytherapy Department, Warsaw, Poland 8 Valencian Institute of Oncology, Department of Radiation Oncology, Valencia, Spain 9 University Hospital Kiel, Department of Radiation Oncology, Kiel, Germany 10 Catalan Institute of Oncology, Department of Radiation Oncology, Barcelona, Spain 11 Masaryk Memorial Cancer Institute, Department of Radiation Oncology, Brno, Czech Republic 12 Hospital Barmherzige Brüder, Department of Radiation Oncology, Regensburg, Germany 13 University Hospital Bern- Inselspital, Department of Radiation Oncology, Bern, Switzerland 14 University of Lübeck / University Hospital Schleswig- Holstein Campus Lübeck, Interdisciplinary Brachytherapy, Lübeck, Germany 15 Sana Hospital Offenbach, Department of Radiotherapy, Offenbach, Germany Purpose or Objective We previously confirmed in a phase 3 randomised trial that accelerated partial breast irradiation (APBI) using interstitial multicatheter brachytherapy in the treatment of early-stage breast cancer after breast-conserving surgery (BCS) is non-inferior to whole-breast irradiation (WBI) regarding local control and overall survival. Here, the 5-year results of patient reported quality of life (QOL) data are presented. Material and Methods This randomised, phase 3 trial was conducted at 16 European hospitals and medical centres (2004 - 2009).