ESTRO 2021 Abstract Book

S1124

ESTRO 2021

has presented BF since the end of treatment with a median PSA nadir 0,18ng/mL (0,01-0,40), in an unspecified nadir PSA patient due to short follow-up period. All patients are alive at the present time. And acute/late gastrointestinal-urinary toxicities (CTCAE v 4.03): 33,3% (5/15) patients had acute urinary toxicities Grade > 3. In addition, Rectitis Grade > 2 were observed in 13,3% (2/15); No acute grade 4/5 toxicities were noted. Chronic toxicity, no grade Grade > 3 toxicities were noted. Conclusion Our data suggest that the treatment of locally recurrent prostate cancer with salvage External Beam Radiotherapy could provide adequate disease control and result in a safe technique that provides the patient with an alternative in the natural history of their disease. PO-1372 First institutional analysis between ultra vs moderate hypofractionated regimens in prostate cancer G. Ferraris 1 , P. Andrada 1 , A. Gomez Palacios 1 , L. Alvarado 2 , F. Eduardo 3 , L. Caussa 1 , F. Diego 1 , D.V. Maria Fernanda 1 1 Centro de Radioterapia Dean Funes, Radiotherapy, Cordoba, Argentina; 2 Centro de Radioterapia Dean Funes, radiotherapy, Cordoba, Argentina; 3 Genesis Care, Radiotherapy, Aventura-Florida, USA Purpose or Objective To evaluate efficacy and acute and chronic gastrointestinal (GI) and genitourinary (GU) toxicities between extreme hypofractionation (SBRT) and moderate hypofractionation (HM). To date, there are no reported phase III studies comparing both treatments. Materials and Methods We performed an institutional retrospective comparative review, which included patients with localized prostate cancer. Patients were older than 18 years, with histological confirmation of T1a - T2cN0M0 prostate adenocarcinoma and a Performance Status of 0 or 1 at the time of treatment were included in the analysis. Patients received treatment between October 2016 and June 2018. 184 men (95 HM and 99 SBRT) were included in the analysis. The patients received radiotherapy to the prostate with or without inclusion of the seminal vesicles, with MH schemes (62-60 Gy in 20 fractions for 4 weeks), or extreme hypo fractionation schemes (36.25-40 Gy in 5 fractions over 2 weeks). The treatments were delivered with VMAT / IGRT techniques with Varian Trilogy linear accelerator and 6 MeV photon beam. Adverse events were assessed according to the Common Terminology Criteria for Adverse Events (CTCAE version 4.0), and PSA values were obtained from analyzes performed in non-centralized laboratories. Efficacy was evaluated in terms of biochemical relapse-free survival (BRFS), for which biochemical progression-free survival curves were obtained by the Kaplan-Meier method. The difference in proportions test was used to perform a comparative analysis of GU and GI toxicities between the schemes, based on Fisher's Exact Test. All analyzes were performed using the InfoStat® platform. Results Median follow-up was 19.5 months (3.2 - 36 months). The mean age of the patients was 69 years in both groups. Significant prognostic factors in the univariate analysis for Freedom From Biochemical Failure (FFBF) included Gleason score> 8 (p = 0.05) or PSA> 20 ng / ml (p = 0.008). Multivariate analysis revealed that only high-risk group is a significant predictor of FFBF (p = 0.05). The proportion of patients free of biochemical failures at 19.5 months was 95.8% in the HM group and 96.2% in the SBRT group (p = 1.00). Both acute G1-2 acute (p <0.001) and chronic (p 0.01) GU toxicity were significantly lower in the group that received SBRT. There were no significant differences in acute toxicity for both: GU G3-4 (P: 0.26) and GI G1-2 (p = 0.44). There was no difference between G3-4 GU or GI chronic toxicities between both treatments (p = 1). There were no acute G3-4 GI toxicities in any of the arms. No treatment-related or other deaths were reported. Conclusion SBRT did not present differences in efficacy compared to the moderate hypofractionation scheme, with lower grade 1 and 2 genitourinary toxicity, and could be considered as a treatment option for external beam radiotherapy in localized prostate cancer. These findings require further validation through ongoing prospective trials. PO-1373 Targeted biopsies are redundant in mp-MRI and PSMA-PET proven radiorecurrent prostate cancer M. Peters 1 , M. van Son 1 , M. Rasing 1 , J. Lagendijk 1 , M. Moerland 1 , S. van de Pol 1 , W. Eppinga 1 , T. Jonges 2 , F. Wessels 3 , B. de Keizer 4 , J. Noteboom 5 , J. van der Voort van Zyp 5 1 University Medical Center Utrecht, Department of Radiation Oncology, Utrecht, The Netherlands; 2 University Medical Center Utrecht, Department of Pathology, Utrecht, The Netherlands; 3 University Medical Center Utrecht, Department of Radiology, Utrecht, The Netherlands; 4 University Medical Center Utrecht, Department of Nuclear Medicine, Utrecht, The Netherlands; 5 University Medical Center Utrecht, Department of Radiation Oncology , Utrecht, The Netherlands Purpose or Objective Radiorecurrent prostate cancer is conventionally confirmed using systematic and/or targeted biopsies. The availability of multiparametric (mp) MRI and more recently prostate specific membrane antigen (PSMA) PET-CT has increased diagnostic accuracy in the radiorecurrent setting. It is unknown whether pathology verification remains necessary with these imaging modalities combined. Especially in the radiorecurrent setting where they might have higher diagnostic accuracy compared to diagnosis of primary prostate cancer due to fibrotic and inactive surrounding prostate tissue. Materials and Methods Patients treated with MRI guided focal salvage high dose rate (HDR) brachytherapy from July 2015 to January 2018 were included in the current analysis. Patients were part of a prospective cohort and phase II study (PRECISE; https://www.trialregister.nl/trial/6827) investigating a single 19 Gy dose to the recurrent tumour