ESTRO 2020 Abstract Book

S619 ESTRO 2020

balloon filled-up with 100cc air to minimize rectal movements. Nineteen patients (18.27%) were treated in a Versa-HD Linac and Intra-fraction motion 4D image guidance with Clarity system (Elekta). 76P (73.08%) received premedication with alpha-1 receptor antagonist and 25p (24.04%) received androgenic deprivation therapy (ADT). Biochemical failure was assessed with Phoenix definition and toxicities were scored with Common Terminology Criteria for Adverse Events (CTCAE) V.5.

Conclusion To the best of our knowledge, this study includes the largest single center European cohort of patients with localized PCa treated with robotic SBRT. It also includes one of the largest cohorts of high-risk patients (n=109, 51.2%) treated with this ultrahypofractionated mode of radiation therapy. With the mFU of 5.3 years, the efficacy results are promising in all risk groups and the toxicity is low. However, larger studies with longer follow-up times are needed to proof the robustness of the SBRT as one of the primary treatment modalities in localized PCa. PO-1176 Ultra-hypofractionated SBRT for localized prostate cancer: single institution experience A. Acosta Rojas 1 , A. Montero Luis 1 , J. Valero Albarran 1 , O. Hernando Requejo 1 , E. Sanchez Saugar 1 , R. Ciervide Jurio 1 , M. Garcia-Aranda 1 , X. Chen 1 , R. Alonso Gutierrez 1 , M.A. De la Casa 2 , D. Zucca 2 , P. Fernandez Leton 2 , M.C. Rubio Rodriguez 1 1 University Hospitals Madrid Sanchinarro & Madrid Puerta del Sur, Radiation Oncology, Madrid, Spain ; 2 University Hospitals Madrid Sanchinarro & Madrid Puerta del Sur, Medical Radiation Physics, Madrid, Spain Purpose or Objective To evaluate clinical outcomes and tolerance toxicity for localized prostate cancer treated by ultra- We reviewed 104 patients with a median age of 70yo (52- 82) diagnosed with low (51.92%), intermediate (47.12%) and high risk (0.96%) prostate cancer treated with a definitive-intent SBRT between 2016-2019. Patients´ characteristics are detailed in image 1. Dose prescription for the entire cohort was 36.25Gy in 5 fractions of 7.25Gy on every-other-day. Treatments were delivered in a lineal accelerator Novalis (Brainlab) with daily inter and intra-fraction orthogonal- Xray image guidance (Exactrac®) in 85p (81.73%). All had two gold-fiducials markers placed transperineally into the prostate guided by transrectal-ultrasound and endorectal hypofractionated SBRT. Material and Methods

Results With a median follow-up of 16 months (2-40) all patients are alive; no distant relapse was observed and there was just one (0.96%) biochemical-local prostate relapse confirmed by choline PET-CT at 28.63 months in favorable- intermediate risk group patient. No genitourinary (GU) toxicity > grade 3 and gastrointestinal (GI) > grade 2 were observed, analysis of medians and acute toxicity is described in image 2. Prostatic median volume was 67.53cm 3 (18.36-188.32). We observed no worsening acute GI and GU toxicity related to the prostatic median volume.