ESTRO 2021 Abstract Book

S1115

ESTRO 2021

Nadir value between both groups reached, 0.227 with BQT and 0.618 with SBRT (p= 0.006) as well as the percentage of PSA decrease respect to diagnosis, -97.27% BQT and -92.25% SBRT (p=0. 001). The time of reaching nadir PSA, 85.45% of patients treated with BQT reached PSA after 2.5 years of follow-up and 57.78% of those treated with SBRT (p=0.004). Differences were only found in the proportion of PSA decline follow-ups between 30 months and 4 years. With a median follow-up of 61.16 months 6 patients presented recurrences, 3 from each group (p=0.8) and 16 patients died due to other causes. Conclusion LDR brachytherapy and SBRT are two equally effective therapies in the treatment of low and intermediate-risk prostate cancer, with differences in toxicity profile and PSA response during follow-up. PO-1358 Does brachytherapy boost improve biochemical control in intermediate and high-risk prostate cancer? M. Miszczyk 1 , I. Jabłońska 2 , T. Krzysztofiak 3 , Ł. Magrowski 2 , W. Majewski 4 , R. Suwiński 5 , O. Masri 2 , J. Ciepał 2 , G. Depowska 2 , M. Gmerek 2 , E. Nowicka 2 , P. Wojcieszek 3 1 Maria Sklodowska-Curie National Research Institute of Oncology, Third Radiotherapy and Chemotherapy Department, Gliwice, Poland; 2 Maria Skłodowska-Curie National Research Institute of Oncology, Third Radiotherapy and Chemotherapy Department, Gliwice, Poland; 3 Maria Skłodowska-Curie National Research Institute of Oncology, Brachytherapy Department, Gliwice, Poland; 4 Maria Skłodowska-Curie National Research Institute of Oncology, Radiotherapy Department, Gliwice, Poland; 5 Maria Skłodowska-Curie National Research Institute of Oncology, Second Radiotherapy and Chemotherapy Department, Gliwice, Poland Purpose or Objective The purpose of this analysis was to investigate whether the combination of external beam radiotherapy (EBRT) and brachytherapy boost (EBRT+BT) is superior to EBRT alone in terms of biochemical control (BC) in the management of intermediate (IR) and high risk (HR) prostate cancer (PC) patients and whether the difference is associated with local biologically effective dose (BED) escalation. Materials and Methods We investigated 1123 patients treated for IR (24.8%) or HR PC (75.2%) with EBRT (90.7%) or EBRT+BT (9.3%) at one institution between 2003 and 2012. Kaplan-Meier curves were used to calculate biochemical control (BC). Log-rank testing and Cox regression were used to compare results between groups. BED was calculated using α/β of 3 for PC. The majority of patients treated with EBRT received 76 Gy in 2 Gy fractions (79%, median BED=126.7 Gy) or equivalent. The patients treated with EBRT+BT received either 54 Gy in 2 Gy fractions followed by 10-11 Gy single fraction BT boost (47.6%, median BED=133.3 Gy), or 46-50 Gy in 2 Gy fx followed by 20-21 Gy two fraction BT boost (51.4%, median BED=171.2 Gy). The endpoint for BC was defined according to the Phoenix definition (Nadir +2 ng/mL), and remaining cases were censored using the date of last known PSA. Results The median age of the patients was 68-years. The 5-year BC was 79%. There was no statistically significant difference in BC between patients treated with EBRT or BT in IR (p=0.74) and HR (p=0.73) PC groups. There was a significant difference between patients receiving lower and higher BED (>135 Gy) fractionation schemes in favour of higher BED, both for IR (5-y BC of 100% vs 81%, p=0.02) and HR group (5-y BC of 92% vs 77%, p=0.02). The BED was inversely associated with risk of BC in univariate analysis (HR=0.98; CI95% 0.97-0.99; p<0.01), and remained an independent prognostic factor in the multivariate analysis (HR=0.97; CI95% 0.96- 0.99; p<0.01) along with Gleason Grade Groups score (HR=1.18; CI95% 1.05-1.32; p<0.01). Conclusion The combination of EBRT and BT boost has the potential to significantly improve biochemical control in IR and HR prostate cancer patients through local BED escalation. The improvement in BC was observed in patients receiving higher BED, as well as a significant association between BED and risk of biochemical failure. PO-1359 PORT impact on biochemical recurrence in pN1 PCa patients: establishing the appropriate RT timing G. Marvaso 1,2 , F.A. Mistretta 3 , I. Sabatini 3 , S. Luzzago 3 , M. Catellani 3 , E. Di Trapani 3 , G. Cozzi 3 , R. Bianchi 3 , G. Cordima 3 , M. Ferro 3 , D. Bottero 3 , D.V. Matei 3 , G. Musi 3,4 , B.A. Jereczek-Fossa 5,2 , O. De Cobelli 3,2 1 IEO, European Institute of Oncolgy IRCCS, Radiation Oncology, Milan, Italy; 2 University of Milan, Oncology and Hemato-Oncology, Milan, Italy; 3 IEO, European Institute of Oncology IRCCS, Urology, Milan, Italy; 4 University of Milan, Onoclogy and Hemato-Oncology, Milan, Italy; 5 IEO, European Institute of Oncology IRCCS, Radiation Oncology, Milan, Italy Purpose or Objective The optimal management strategy for pN1 prostate cancer (PCa) patients after primary surgery is still debated. Moreover, an important unmet need is how to find ideal candidates for adjuvant radiotherapy (aRT, defined as RT administered within 6 months from surgery), in order to reduce overtreatment, while avoiding dangerous delays in treatment administration. To address these voids, we retrospectively compared long-term biochemical recurrence rates (BCR) in pN1 patients that underwent aRT vs. observation + /- salvage RT (sRT) after robot-assisted radical prostatectomy (RARP). Materials and Methods We retrospectively identified 500 pN1 PCa patients without distant metastases, treated with RARP and extended pelvic lymphadenectomy at a single high volume centre between 2010 and 2020. We lately excluded all patients with an inadequate number of lymph nodes removed (less than 10) or with high burden nodal disease (more than 10 positive lymph nodes). Moreover, patients with persistently detectable PSA after RARP and patients with missing data were also excluded. Finally the 220 (44 %) remaining patients represented the study population of the current study. All patients that underwent aRT or sRT received androgen deprivation