ESTRO 2020 Abstract book

S669 ESTRO 2020

radiotherapy (IMRT 51.9%) and stereotactic-ablative radiotherapy (SABR 48.1%) +/- ADT (80.5%). Prostate was irradiated in 5 cases due to synchronous local failure. Twenty-one patients received a second MDT, 7 patients a third MDT and 1 patient 4 MDTs. No grade >2 toxicity occurred. At a median follow-up of 29 months (2-66), local control of treated lesions was 70.1%. The 3-yr bFFS, CRFS, OS and CSS were 20.3%, 76%, 80% and 91% respectively. On multivariate analysis, initial T3-T4 stage and presence of bone metastases at first MDT were associated with worse bFFS (HR 2.75, 95%CI 1.42-5.33 (p=0.003) and HR 2.46, 95%CI 1.27 – 4.76 (p=0.017), respectively). Presentation with M1 de novo disease was associated with worse CRFS (HR 7.56, 95%CI 2.44 – 24.44 (p<0.001).Among nodal-only disease group, no difference in bFFS was seen between IMRT and SBRT modalities (p = 0.45). Among the 16 patients who developed CRPC after MDT, the time to CR (although not statistically significant) was one year longer in patients treated with repeated MDT vs patients treated with one MDT only (2.9 vs 1.9 years, p = 0.27).

Material and Methods Single-centre, retrospective casenote review of 57 patients and 72 abdomino-pelvic lesions treated with 30 Gy in 3 or 5 fractions (5 fractions used for re-irradiation cases) between 2016-18. Survival endpoints were calculated using the Kaplan-Meier method and univariable Cox regression analyses were performed to test association of patient, disease and treatment factors with survival endpoints. Results Primary tumour site was prostate, colorectal and other in 37, 14 and 6 patients respectively. Median follow-up duration was 15.6 months (range 1-39.4 months). PET-CT staging was used in 30/37 prostate and 12/14 colorectal patients. 39, 13 and 4 patients had 1, 2 and 3 lesions treated respectively. 1 year local control (LC), overall survival (OS) and progression-free survival (PFS) was 96.3%, 100% and 80.5% for prostate patients and 66.7%, 90% and 51.9% for colorectal patients respectively. 1 year PFS following SABR with concurrent androgen deprivation therapy was 86% versus 67% without ( p =0.044). No factors evaluated using univariable Cox regression analyses were found to be statistically significant. A trend to inferior PFS was observed where SABR was not the first intervention for relapsed disease (1 year PFS 44.9% versus 78.1%, p =0.2). Further relapses occurred adjacent to the treated node in 5 patients and in distant metastatic sites in 13 patients. For prostate cancer, side of T3 primary disease was associated with side of nodal relapse on chi square analysis 1 year OS and LC rates were good, especially for prostate cancer. Acknowledging the modest follow up duration, PFS was comparable with published results. Most patients relapsed with distant metastases, which reflects the limitations of current staging investigations. 5 patients relapsed adjacent to the treated node, which often precludes further SABR. This suggests a strategy of concurrent treatment of the nodal chain/whole pelvis alongside SABR to the involved node could be advantageous. PO-1181 Metastasis-Directed Therapy influence in clinical outcomes of oligorrecurrent prostate cancer A. Gonzalez Lopez 1 , D. Büchser 1 , F. Suarez 1 , E. Mayrata 1 , F. Casquero 1 , P. Bilbao 1 , A. Gomez-Iturriaga 1 1 Hospital de Cruces, Radiation Oncology, Barakaldo, Spain Purpose or Objective Interest in metastases-directed therapy (MDT) in oligometastatic cancer is increasing due to various studies suggesting this approach may improve clinical outcomes. The aim of this study was to analyze the influence of single or repeated MDT in clinical response of oligorrecurrent From 2012 to 2019, 200 oligometastatic lesions were treated in 77 PCa patients with oligometastatic disease at our institution. Seven patients were de novo M1 disease and there were 7 castrate-resistant (CR) PCa at first MDT. After biochemical failure (bF), patients underwent repeated Choline-PET-CT, and patients with oligorecurrent metastases were offered subsequent MDTs. Descriptive statistics were used to summarize patient characteristics. The Kaplan-Meier method assessed rates of bF-free survival (bFFS) and castrate-resistant-free survival (CRFS). Univariate and multivariate analysis were done to evaluate the influence of prognostic factors in clinical outcomes. Results At first MDT, 159 lesions were treated (71.4% nodal, 26% bone, 2.6% combination of both). Median PSA before Ch- PET was 6.21 ng/mL with a median doubling-time of 8.71 mo. MDT modalities were intensity-modulated ( p =0.008). Conclusion prostate cancer (PCa). Material and Methods

Conclusion Long-term oncologic control may be achievable in patients treated with MDT for oligometastases. Initial T-stage and the presence of bone oligometastases predict worse bFFS and M1 de novo disease is associated with worse CRFS. Subsequent salvage MDT may prolong the time to castrate resistant disease. PO-1182 PSMA-PET is superior to choline-PET based SABR for ADT deferral in oligometastatic prostate cancer C. Deijen 1 , G. Vrijenhoek 1 , W. Vogel 2 , L. Moonen 1 , F. Pos 1 , H. Van der Poel 3 , G. Borst 1 1 The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Radiation Oncology, Amsterdam, The Netherlands ; 2 The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Radiation Oncology & Nuclear Medicine, Amsterdam, The Netherlands ; 3 The Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Urology, Amsterdam, The Netherlands Purpose or Objective In patients with oligometastatic recurrence from hormone- sensitive prostate cancer and no local recurrence, standard treatment is deferred androgen deprivation therapy (ADT). ADT has many side effects and impact on quality of life, e.g. hot flushes, fatigue, decrease of libido, erectile dysfunction, loss of muscle and bone mass and depression. Stereotactic ablative radiotherapy (SABR) can decrease PSA levels and postpone ADT. Modalities to localize disease activity and select patients for SABR are prostate-specific membrane antigen-Positron Emission