ESTRO 38 Abstract book

S853 ESTRO 38

patients (2%) and late grade 3 genitourinary toxicity was observed in 2 patients (1%). Acute and late grade 3 gastrointestinal toxicities occurred in 5 patients (4%) and 2 patients (1%). Lymph node status, pelvic lymph node irradiation, Gleason score, neoadjuvant and concomitant hormonal therapy were significant variables in univariate analysis for bRFS (p<0,05). Multivariate cox regression analysis identified lymph node status as having significant influence on bRFS. Conclusion Postoperative radiotherapy is able to deliver long - term biochemical disease free survival in a substantial number of patients with prostate cancer and high risks features. The majority of recurrences occur outside the treatment field. Modern radiotherapy techniques including IMRT and plan adaptation can reduce toxicity to < 4% in the postoperative setting. EP-1581 Good tolerability of hypofractionated radiation therapy for localized prostate cancer I. Navarro 1 , R. Correa 1 , A. Otero 1 , A. Roman 1 , I. Zapata 1 , A. Fernandez 1 , P. Prieto 1 , S. Segado 1 , C. Jodar 1 , C. Garrido 1 , J.A. Medina 1 , J. Gomez 1 1 Hospital Virgen de la Victoria, Radiation Oncology, Malaga, Spain Purpose or Objective Radiobiological models have determined a low α/β value for prostate cancer (1.5Gy), which suggests a good response with fewer and larger fractions. Some randomized studies of hypofractionation in prostate cancer have been published, reported a high differences in patients selection and in the risk, dose and technical groups used; unable to establish as standard treatment. To analyze the efficacy and toxicities of localized prostate cancer (LPC) patients treated with curative hypofractionated radiotherapy, with a long follow up. These patients were treated outside of a clinical trial. We also evaluate the results in subgroups of patients to determine possible prognostic factors. Material and Methods Retrospective study of 451 patients with LPC treated with hypofractionated radiotherapy, in our institution, between January 2011 and May 2016. The scheme used was 60Gy to 3Gy/fraction, using 3D and volumetric arcotherapy techniques (VMAT). We analyzed the Charlson Comorbidy Index (CCI) as a predictor of survival at 10 years. We also analyzed the age, Gleason score, stage and NCCN risk factors, as well the use of androgen deprivation therapy. Toxicity was evaluated using Common Terminology Criteria for Adverse Events (CTCAE) Version 4.0. The overall survival (0S) was defined as the time from the last day of radiotherapy until the date of last revision. We considered biochemical progression (BP) as Phoenix's definition of more 2ng/dl of PSA nadir; and clinical recurrence (CR) as progression to locoregional lymph- nodes or distant metastases. Results With a median follow-up of 51 months (1.6-88 months), only 1.6% (7 patients) died due to the disease, 89.6% remained alive, 8.4% with biochemical disease, and 3.3% with clinical disease. We observed a high rate of any grade of acute genitourinary toxicity (72.7%), most of them grade 1. But only 20% of chronic genitourinary toxicity was observed. The acute and chronic rectal toxicity showed a low rate, 19.1% and 2.7%, respectively. The radiotherapy technique was significantly associated with acute rectal toxicity. Thus, patients treated with VMAT presented toxicity in 23.9% versus 13.5% with RT3D (p=0.005). The OS at 2, 5 and 7 years was 97%, 88% and 83% respectively. Disease-free survival until BP was 96%, 83.8% and 77.9%. And for the CR, it was 99%, 94% and 92%, respectively. Regarding the survival analysis, the CCI was the only factor with statistical significance for OS (p = 0.00), with a greater number of events being observed in

1 Radiotherapy Center AMETHYST- UMF Iuliu Hatieganu Cluj, Radotherapy, Cluj, Romania ; 2 The Institute of Oncology "Prof Dr Ion Chiricuta" Cluj-NAPOCA, Radiotherapy, Cluj-Napoca, Romania ; 3 Radiotherapy Center AMETHYST, Radotherapy, Cluj, Romania ; 4 Radiotherapy Center AMETHYST, Radotherapy- Physics, Cluj, Romania Purpose or Objective Seminal vesicle (SV) invasion (pT3b) is accepted by all guidelines as criteria for adjuvant radiotherapy (aRT) after radical prostatectomy (RP). Our hypothesis was that the delineation of the tumour bed as per ESTRO guidelines might be improved by MRI fusion into the planning. Material and Methods Twelve pT3bNo, cM0 prostate adenocarcinoma patients (50 % with peri-vesicular extension) having received aRT in our institution during 2016-2017 were retrospectively contoured by fusing the preoperative prostate MRI into the treatment planning. The treated (postoperative) CTV and PTV (+5 mm) were according to the ESTRO delineation guidelines; 66Gy/33 fr IMRT/VMAT with daily IGRT were delivered. The preoperative MRI SV length was divided in 3 levels (lower, middle and upper third), expanded to PTV with the same margin as in the actual plan (5mm). We analysed the “geographic miss” of the postoperative dosimetry applied to the “preoperative SV adapted “delineation. Results Assuming all of them would have had peri-vesicular extension, the coverage of the SV bed was suboptimal for 8.3 % of the lower third, 25 % of the middle third and 16.6 % of the upper third of the SV, leaving only 50 % accurate PTV coverage! Conclusion Integrating the preoperative MRI into the RT planning might improve the target coverage in a substantial number of pT3b cases. We suggest that future ESTRO guidelines shall consider fusion of the prior prostatectomy prostate MRI into the treatment planning for adjuvant or salvage RT. EP-1580 Adjuvant radiotherapy in prostate cancer patients–bRFS and toxicity using adaptive IMRT technique P. Toncheva 1 , N. Volegova - Neher 1 , K. Henne 1 , A. Grosu 1 , S. Kirste 1 1 Uniklinik Freiburg, Radiation Oncology, Freiburg, Germany Purpose or Objective In this retrospective study we assessed local tumor control and biochemical recurrence free survival (bRFS) in a single center cohort of prostate cancer patients who underwent postoperative radiation therapy in adaptive IMRT technique. Furthermore we investigated acute and long – term genitourinary and gastrointestinal toxicities. Material and Methods We evaluated 140 high risk prostate cancer patients who were treated between 2010 and 2014 within 6 months after radical prostatectomy. Depending on bladder and rectum volumes the planning target volume (PTV) was adapted. Median prescription dose applied to the prostate bed was 66,6 Gy in 37 fractions. 39 out of 62 node positive patients received up to 54 Gy to the pelvic lymph nodes. Descriptive statistics as well as uni- and multivariate analysis were performed. Results Median follow up was 48 months (2 – 86 months). The 4 - year overall survival rate was 94%. 4 - year bRFS was 55%. 51 out of 140 patients developed a recurrence. Biochemical recurrence was observed in 15 patients, 30 patients developed a recurrence outside the treatment field and 6 patients had a recurrence inside the treatment field. Acute grade 3 genitourinary toxicity occurred in 3