ESTRO 2020 Abstract book

S670 ESTRO 2020

Clinical data, early and late GI toxicity (RTOG scale) and dose-volume parameters were collected and analyzed. Based on literature, dosimetric parameters such as V15, V30, V40, V45, V50, V60, V70, Dmax, Dmean and median volume of sigma were evaluated. Sigma was contoured 2 centimeters above the PTV with an expansion of 1 centimeter in all directions. Results Fifty-eight patients with prostate acinar adenocarcinoma treated from 2015 to 2018 were analyzed; median age was 72 (range 45-81). Hormonal therapy was administered in 43 patients (74%). Treatment intent was exclusive, adjuvant or salvage in 17 (29.3%), 18 (31%) and 13 (biochemical: 20.7%; macroscopic recurrence: 1.7%) patients, respectively. According to treatment doses (66- 70Gy vs 72-78Gy) and volumes (whole pelvis vs no-whole pelvis), sigma dose-volume parameters were evaluated in 4 subgroups of patients (Table). The median follow-up was of 18.45 months (range 6-39.5). Early and late Grade 1 GI toxicity (diarrhea, tenesmus, rectal bleeding) was reported in 12% and 5.2% patients, respectively; early and late Grade 2 GI toxicity (diarrhea, tenesmus, rectal bleeding, fecal incontinence) was reported in 10.3% and 1.7% patients, respectively and no early and/or late GI toxicity > Grade 2 was reported. Overall, limited volumes of sigma in treatment field was reported in all subgroups with no significant differences between the 4 subgroups. Furthermore, high doses were delivered to limited volumes of sigma with no early and late GI toxicity > G2. Conclusion Our results on a limited number of patients did not show Grade > 2 GI toxicity and high doses (V50%, V60%, V70%) were delivered only to small volumes of sigma, although specific constraints for sigma were not applied during planning optimization. These preliminary data seem to be promising and applicable to daily clinical practice, pointing out the ability of IMRT/VMAT to reduce acute and late toxicity. The study is still ongoing on a larger number of patients and a longer follow-up. PO-1184 The significance of nomograms for predicting node metastasis in 68ga-PSMA-PET/CT in prostate cancer C. Onal 1 , O.C. Guler 1 , N. Torun 2 , M. Reyhan 2 1 Baskent University Adana Dr Turgut Noyan Research and Treatment Center, Department of Radiation Oncology, Adana, Turkey ; 2 Baskent University Adana Dr Turgut Noyan Research and Treatment Center, Department of Nuclear Medicine, Adana, Turkey Purpose or Objective To evaluate the accuracy of clinical parameters and nomograms in predicting 68 Ga-PSMA positive lymph node metastasis as initial staging examination for prostate cancer patients. Material and Methods The clinical parameters of 271 treatment-näive prostate cancer patients were retrospectively analyzed. All patients had 68 Ga-PSMA-PET/CT for initial staging procedure. The correlation between serum PSA, SUV max of primary tumor and lymph node metastasis was evaluated. The risk of lymph node involvement was calculated using Roach formula (RF), Yale formula (YF) and Partin nomogram (PN) and compared with 68 Ga-PSMA-PET/CT

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.