ESTRO 2020 Abstract Book

S629 ESTRO 2020

At the time of the analysis, disease free survival was 63.6% compared to 34% in the 68Ga-PSMA and Choline PET group, respectively. . No difference was observed regarding the DPFS between the two arms (p-value 0.06). The ADT administration rate was higher after PET-Choline guided SBRT (p-value 0.0003) due to the higher incidence of polymetastatic disease after a first-course of PET-Choline SBRT comparing to 68Ga-PSMA guided SBRT, as shown in figure 1. Conclusion In the present comparative analysis, SBRT-guided by 68Ga- PSMA PET allowed to obtain a higher rate of ADT free patients if compared to SBRT-guided by 18F-Choline PET, in the setting of oligorecurrent castration-sensitive PC. Randomized trials are strongly advocated. PO-1194 MR-based adaptive IGRT of prostate cancer: feasibility, plan adaptation and acute toxicity D. Wegener 1 , F. Paulsen 1 , C. De Colle 1 , D. Thorwart 2 , U. Grosse 3 , A. Othman 3 , S. Afat 3 , J. Bedke 4 , A. Stenzl 4 , K. Nikolaou 3 , D. Zips 5 , A. Müller 5 1 University Hospital Tübingen, Department of Radiation Oncology, Tübingen, Germany ; 2 University Hospital Tübingen, Department of Radiation Oncology- Section Medical Physics- German Cancer Consortium DKTK- partner site Tübingen- and German Cancer Research Center DKFZ- Heidelberg- Germany, Tübingen, Germany ; 3 University Hospital Tübingen, Department of Radiology, Tübingen, Germany ; 4 University Hospital Tübingen, Department of Urology, Tübingen, Germany ; 5 University Hospital Tübingen, Department of Radiation Oncology- German Cancer Consortium DKTK- partner site Tübingen- and German Cancer Research Center DKFZ- Heidelberg- Germany, Tübingen, Germany Purpose or Objective Conventional fractionated dose-escalated radiotherapy (RT) up to 80 Gy +/- androgen deprivation therapy (ADT) is a standard treatment option for prostate cancer (PC). Since ADT reduces prostate volume by ~10% per month a significant decrease of the target volume and increased overlap with organs at risk at the end of IGRT might be expected. Therefore, we studied whether multiparametric MRI-based treatment planning and threshold-/constraint- based adaption of the radiation treatment plan using a weekly MRI is able to reduce G2+ gastrointestinal (GI) and genitourinary (GU) side effects within a prospective phase II study (M-base Pro 1.0). Material and Methods Patients with MRI-staged PC (cT1-3b N0 M0) were included in this prospective study (ClinicalTrials.gov Identifier: NCT02724670). Treatment consisted of 78 Gy (39 frx) to prostate and seminal vesicles (low/intermediate/high risk or cT3b: 0/1/2cm or complete SV). ADT was given according to national guidelines. Diagnostic 3T MRI was performed at diagnosis, after neoadjuvant ADT (treatment planning), at week 2 and 7 of RT. 1.5 T MRIs without gadolinium (T2w, DWI) were performed before and weekly during RT. Daily Image-guided RT (IGRT, gold fiducials, cone-beam CT) was planned with a PTV margin of 6 mm, dorsally 5 mm. The need for plan adaption was weekly checked by MRI. In case of prostate volume changes ≥25% / ≥20ml or unmet predefined OAR-constraints the radiation treatment plan was adapted. Acute toxicity (RTOG, CTC) was scored before RT start, weekly during RT and 3 months post RT in the predefined exploratory cohort All 25 patients of the exploratory cohort were able to follow the study protocol. Plan adaptions were performed in 28% of patients (n=7). CTC urinary frequency decreased from baseline with 12% (G1) to 4% (G1) after neo-ADT, increased during IGRT (climax at week 8: G1=75%; G2=8%) and decreased three months after IGRT to 26% of G1. Acute RTOG bladder toxicity (Fig. 1) increased from 4% (G1) at (n=25). Results

baseline to week 8 (G1= 80%, G2=8%) and decreased again three months later (G1=8%). CTC proctitis was absent at baseline and reached 40% (G1) and 16% (G2) at week 8 and decreased to 18% of G1 3 months post RT. Acute RTOG rectum toxicity (Fig. 2) increased from baseline (0%) to 60% of G1 at week 8 and decreased to 8% of G1 three months after IGRT. No grade 3+ acute toxicity occurred in any scored item. Conclusion In this single-arm prospective study we were able to demonstrate feasibility of an ambitious imaging protocol with MR-based adaptive IGRT. In addition, the extent of acute toxicity of this weekly adaptive IGRT in PC was very encouraging. PO-1195 Impact of Adjuvant Radiotherapy in node positive prostate cancer patients G. Corrao 1 , M. Montesano 1 , G. Marvaso 1 , G.C. Mazzola 1 , J. Franzetti 1 , C. Fodor 1 , D. Zerini 1 , S. Gandini 2 , S.P. De Angelis 2 , F. Cattani 3 , O. De Cobelli 4 , R. Orecchia 5 , B.A. Jereczek-Fossa 1 1 European Istitute of Oncology, Radiotherapy, Milan, Italy ; 2 European Istitute of Oncology, Epidemiology and Biostatistics, Milan, Italy ; 3 European Istitute of Oncology, Medical Physics, Milan, Italy ; 4 European Istitute of Oncology, Urology, Milan, Italy ; 5 European Istitute of Oncology, Scientific Directorate, Milan, Italy Purpose or Objective Large, prospective randomized studies have demonstrated that low volume-nodal prostate cancer (PCa) patients (one or two positive lymph nodes) have significantly higher survival rates compared to ones with higher volume-nodal disease, regardless of adjuvant treatment administrated. Anyway, the management of this setting of patients is still under debate. The aim of this retrospective study was to assess the impact of adjuvant radiotherapy (aRT) in patients with pathological positive lymph nodes (pN1) in terms of Overall Survival (OS), biochemical, clinical and distant metastasis Progression Free Survival (b-PFS, c-PFS and m-PFS) and to correlates oncological outcomes with tumor characteristics. Urinary and rectal toxicities were evaluated. Material and Methods Patients with pN1 PCa, treated between 2008 and 2018 with radical prostatectomy, extended pelvic lymph node dissection, aRT within 6 months from surgery and +/- hormonal therapy, were included in this mono- institutional cohort. Log-rank tests and Cox proportional hazards were used to compare and identify independent prognostic factors of biochemical and clinical recurrence, with adjustment for relevant covariates. Results Hundred eighty-seven patients were included in this study with a median follow-up of 49 months (range 3-172). At 5- years, we observed b-PFS, c-PFS, m-PFS and OS of 56 %, 68 %, 71 % and 94 % respectively. To perform the analysis, patients were divided in two groups according to the most informative cut-off of positive nodes. A significant statistical impact was observed for patients who harbored 5 or more lymph-nodes (Figure. 1). At univariate analysis, vascular invasion and the number of positive nodes were significant predictors of b-PFS (all p < 0.002). Multivariate analysis confirmed an increased risk of biochemical relapse for initial PSA value (iPSA) (HR= 1.01 and 95% CI: 1.00 to 1.02 and p-value= 0.021), a reduced risk in patients without vascular invasion (HR= 0.5 and 95% CI: 0.31 to 0.79 and p-value= 0.003) and number of lymph-nodes from 1 to 4 vs 5 or more (HR= 0.47 and 95% CI: 0.27 to 0.83 and p- value= 0.010) (Table. 1). Multivariate proportional Cox hazard models confirmed also significantly reduced risk of c-PFS and m-PFS for ISUP < 3 and lymph-nodes <5. OS was correlated only with the increase in iPSA value (HR= 1.02 and 95% CI: 1.01 to 1.03 and p-value= 0.002).