ESTRO 2020 Abstract book

S676 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

different in patients submitted to post-operative RT and ENI. Very low UCLA sexual points decrease further after the treatment (p=0.000) (basal vs 1m); ADT and surgery induce lower 1m points. Acute (CTCAE 4.0) G3-4 grades were absent. G1-2 rectal and bowel toxicity is lower than 30%, G1-2 urinary is 62% (G1=46.5%; G2=16%). No differences have been observed according the treated volume, but a slightly more frequent G2 bowel toxicity in the ENI group Conclusion The study is still recruiting (till February 2020). These preliminary data show an elderly, relatively healthy population. RT seems to be well tolerated at the 1m follow up interval, in both ENI and no-ENI cases. Longer follow up data are needed before drawing any conclusion, being as important as treatment data PO-1193 18F-CHOLINE PET/68Ga-PSMA PET SBRT in oligorecurrent prostate cancer: comparative analysis R. Mazzola 1 , G. Napoli 1 , G. Francolini 2 , L. Triggiani 3 , L. Nicosia 1 , V. Figlia 1 , N. Giaj-Levra 1 , F. Ricchetti 1 , M. Rigo 1 , F. Cuccia 1 , L. Livi 2 , S.M. Magrini 3 , M. Salgarello 4 , F. Alongi 1 1 Sacro Cuore Don Calabria Cancer Care Center, Advanced Radiation Oncology, Negrar, Italy ; 2 A.O.U. Careggi- University of Florence, Radiation Oncology, Florence, Italy ; 3 ASST Spedali Civili di Brescia - Brescia University- , Radiation Oncology, Brescia, Italy ; 4 Sacro Cuore Don Calabria Cancer Care Center, Nuclear Medicine, Negrar, Italy Purpose or Objective Aim of the present analysis is to compare the impact of 18F-Choline and 68Ga-PSMA PET-CT guided metastases directed therapies (MDT) in a cohort of patients affected by castration sensitive oligorecurrent prostate cancer (PC). Material and Methods The present study is a retrospective multicenter analysis conducted at three Italian Academic Centers. Inclusion criteria of the present analysis were: i) histologically confirmed diagnosis of prostate carcinoma, ii) patients affected by biochemical relapse after primary tumor treatment (radical prostatectomy or radical radiotherapy), iii) oligorecurrent PC, defined as the presence of 1-3 hypermetabolic lesions detected by means of 18F-Choline or 68Ga-PSMA PET-CT, iv) 18F-Choline and 68Ga-PSMA PET- CT performed in a single Nuclear Medicine, v) patients treated with upfront SBRT without hormonal therapies, vi) SBRT delivered with a dose of at least 5 Gy per fraction to a biological effective dose (BED) of at least 80 Gy using an α/β ratio of 2 Gy. In case of oligoprogression after MTD, a second-course of SBRT was generally proposed if less than of ≤3 new lesions were diagnosed, outside the previous irradiated field. In the remaining cases, androgen deprivation therapy was administered. The primary endpoint was the distant progression free survival (DPFS) after SBRT, defined as the interval between the end of SBRT and the detection of a new metastasis outside the field of irradiation. Secondary endpoints were: overall survival (OS, local control (LC) and ADT-free survival. Results 118 lesions in 88 patients were analyzed. Forty-four (50%) patients underwent SBRT by means of 68Ga-PSMA PET/CT whereas the remaining 50% by 18F-choline PET/CT. The median follow-up was 25 months (range 5-87). For the entire population of study, OS and LC were 100%. In 48 patients (54.5%) a distant progression occurred. The DPFS was 22.8 months (range, 14.4-28.8 months). Median PSA value before SBRT was 2.07 ng/ml in the Choline PET cohort, and 0.6 ng/ml in the PSMA-PET arm.