ESTRO 2020 Abstract Book

S622 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).

Tomography (PSMA-PET) and choline-PET. PSMA-PET has a higher sensitivity, but it is unknown if this results in better outcomes for SABR. We hypothesize that PSMA-PET based SABR results in longer response duration and longer delay in starting ADT, due to a lower risk of missing small metastases. In this study we compared the clinical outcomes of patients selected for SABR with PSMA-PET and choline-PET. Material and Methods Patients diagnosed with oligometastatic recurrence (≤ 4 metastases) of prostate cancer without evidence of local recurrence based on PSMA-PET or choline-PET, who were treated with SABR were included. Primary endpoints were 1) PSA response after SABR, defined as decrease in PSA level of ≥ 25% compared with the last measured PSA level before start of SABR (according to previous PSA evaluating studies) and 2) PSA rise after SABR, defined as 2 consecutive PSA rises >0.2ng/mL after prostatectomy and rising PSA level >2ng/mL above the nadir in patients treated with radiotherapy. Secondary endpoint was ADT- free survival. Results Fifty patients with in total 72 lesions treated with SABR from January 2012 until December 2017 were included. In 40 patients PSMA-PET was used for detection of metastases and in 10 choline-PET. Median follow-up was 22.6 months. SABR resulted in PSA response in 28/50 patients (56%). Of PSMA-PET imaged patients 57.5% (n=23/40) had PSA response compared to 50% (n=5/10) of choline-PET imaged patients. The median response duration of PSA responding patients imaged by PSMA-PET was 24.8 months (95% CI, 14.4-35.1) and 14.7 months (95% CI 4.7-24.7) for choline- PET patients (p=0.005). Non-PSA responding patients imaged by PSMA-PET had a longer time to PSA rise than patients imaged by choline-PET (12.0 months (95% CI, 7.9- 16.1) vs. 7.8 months (95% CI, 7.8-7.9)) (p=0.03). ADT-free survival of PSMA-PET diagnosed patients was 27.5 months (95% CI, 18.4-36.7) compared to 14.9 months (95% CI, 5.7- 24.1) for choline-PET diagnosed patients (p=0.03). Conclusion The results of our small group choline-PET patients are in line with previously published data. PSMA-PET is superior to choline-PET to select patients with oligometastatic recurrent prostate cancer without local recurrence for SABR to postpone ADT, as it results in a longer response duration and prolonged ADT-free survival. PO-1183 Do we need sigma constraints in era of intensity-modulated radiation therapy for prostate cancer? F. Patani 1 , D. Fasciolo 1 , A. Allajbej 1 , M. Trignani 1 , M. Di Tommaso 1 , A. Augurio 1 , A. Vinciguerra 1 , L. Caravatta 1 , D. Genovesi 1 1 “SS. Annunziata” Hospital, Radiation Oncology Unit, Chieti, Italy Purpose or Objective Intensity and/or volumetric modulated radiotherapy (IMRT, VMAT) have demonstrated to significantly reduce high doses to rectum and bladder and related acute and late toxic effects. Currently, these radiotherapy techniques represent the standard of care in the treatment of prostate cancer. Moreover, the wide atlases availability allows a high accurate definition of treatment volumes and organs at risk (OARs) with likely outcomes improvement. According to RTOG atlas, sigma represents to date an OAR in prostate radiotherapy. However, dose constraints for sigma are up to now not available. In this context, the aim of this study was to analyze sigma dose-volume parameters and intestinal (GI) toxicity in prostate cancer patients treated with IMRT/VMAT. Material and Methods A retrospective evaluation of all patients with sigma included in the treatment field treated in our Institution and with a minimum follow-up of 6 months was conducted.

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