ESTRO 38 Abstract book

S854 ESTRO 38

patients (53.9%) with VMAT.The median follow-up was 51 months (maximum 88 months). The volume and the mean rectal and bladder doses were slightly higher in VMAT compared to 3D (Table 1). Regarding toxicity, we found differences between both groups. An increased acute rectal toxicity (any grade) was seen in 58 patients (23.9%) in VMAT group, compared to the group of 3D-RT with 28 patients (13.5%) (p = 0.005). No statically difference was found in the rest of parameters analyzed, and no difference in chronic toxicity between both techniques (Table 2). The percentage of patients in the VMAT group had higher risk factors with significant differences (age > 68 years, seminal vesicles included, Gleason score > 7, stage and NCCN group risk), in univariate and multivariate test. No difference in biochemical and clinical failure were observed.

the patients with CCI >/= to 3.5 (Image 1). Moreover, those patients with high or very high risk, presented a lower survival (p=0.032), as well as patients with higher Gleason (p=0.04).

Conclusion Hypofractionated radiotherapy with escalated doses in prostate cancer is a well-tolerated treatment, with a low rate of chronic toxicity and with a high efficacy. The hypofractionation benefits allow reducing the number of sessions thus improving the quality of life, the use of resources and decreases the cost of treatment. EP-1582 Differences between 3d and vmat in hypofractionated radiation therapy for localized prostate cancer I. Navarro 1 , R. Correa 1 , A. Roman 1 , A. Otero 1 , A. Fernandez 1 , P. Prieto 1 , M.J. Garcia 1 , I. Garcia 1 , R. Ordoñez 1 , I. Jerez 1 , J.A. Medina 1 , J. Gomez 1 1 Hospital Virgen de la Victoria, Radiation Oncology, Malaga, Spain Purpose or Objective External beam radiotherapy (RT) is an appropriate treatment option for patients with localized prostate cancer. Some studies have shown superiority of dose escalation in the control of the disease. However, an increase in toxicity has been described with these regimens. The use of intensity modulated radiotherapy (IMRT) with volumetric arcotherapy (VMAT) and image- guided radiotherapy (IGRT) makes possible to carry out the treatment without increasing side effects. The objective is to analyze the differences between 3D and VMAT techniques in the toxicity profile, biochemical failure and clinical recurrence. Material and Methods Retrospective study of a large number of patients with localized prostate cancer treated with hypofractionated radiotherapy (60Gy to 3Gy per fraction) with radical intention using 3D and VMAT techniques, both with daily image verification with cone beam CT (XVI), in our institution, between January 2011 and May 2016.After analyzing dose-volume histogram (DVH), those cases with satisfactory coverage of planning target volume (PTV) and dose constraints for organ at risk, were treated with 3D technique. More complex cases were treated performing VMAT. From May 2015, due to the better conformation treatment planning, translated into better DVH results and a shorter treatment time, all patients were treated with VMAT. The variables analyzed were the age, stage, Gleason score, NCCN risk group and seminal vesicles treatment, using univariate and multivariate analysis. P values<.05 were considered statistically significant. Results We analyzed 451 men with prostate cancer with a range of age between 45 and 81 (median 68 years). 208 patients (46.1%) were treated with 3D radiotherapy, and 243

Conclusion We did not find significant differences between the two techniques used, except in acute rectal toxicity. This apparent difference may be due to the fact that the VMAT technique was considered to be the choice in those cases that required a greater volume of irradiation, when including the seminal vesicles, so that this increased toxicity could be more related to the total volume rather than to the technique employed. EP-1583 Feasibility of postprostatectomy dose escalated salvage radiotherapy by reduction of bladder dose G. Sancho Pardo 1 , E. Acosta 1 , L. Tilea 1 , A. Soto 1 , A. Nuria 1 , G. Gómez de Segura 1 , J. Craven-Bartle 1 1 Hospital de la Santa Creu i Sant Pau, Radiation Oncology, Barcelona, Spain Purpose or Objective After radical prostatectomy, salvage RT with doses over 66 Gy to the prostate bed may confer a benefit but also an increased risk of genitourinary (GU) toxicity. In this setting, we analyse the acute and late GU toxicity and their association with dosimetric parameters. Material and Methods We performed a retrospective study in 190 patients (pt) with prostate cancer who had biochemical failure after radical prostatectomy. Since june 2011, all patients underwent a multiparametric-MRI to investigate the site of recurrence before planning the radiation treatment. Clinical and planning target volumes (CTV and PTV) were contoured according to the EORTC guidelines. Elective pelvic irradiation was indicated in patients without