ESTRO 2021 Abstract Book

S1121

ESTRO 2021

stereotactic body radiotherapy (SBRT). However, one of the main criticism of nodal SBRT alone may be avoidance of prophilactic irradiation of prostate bed and elective nodal volumes. For this reason, we analysed recurrence patterns after nodal SBRT in patients affected by pelvic oligometastatic relapse after RP, and androgen deprivation therapy (ADT) free survival in this population. Materials and Methods Data about 68 patients consecutively treated in 5 different institutions for pelvic oligorecurrent disease were retrospectively reviewed and collected. Inclusion criteria were BCR after RP and imaging showing < 3 metachronous lymphoadenopaties under aortic bifurcation. Patients underwent SBRT on all sites of disease. Concomitant ADT was allowed. Patients treated on prostate bed +/- pelvic nodal volumes were excluded from the analysis. Results After a median follow-up of 23 months (IQR 14-47), 43 patients had post-SBRT radiological evidence of relapse, for a median disease-free survival (DFS) of 18 months (95% CI 9-29). Concomitant ADT was administered in 13 (19.1%) patients. Considering only patients in whom concomitant ADT was not administered, median ADT-free survival was not reached. Overall, 8 (11.8%), 18 (26.4%) and 17 (25%) patients had prostate bed only, pelvic nodal or distant relapse, respectively. Concomitant ADT, ISUP pattern at diagnosis < or > 3, time to relapse < or > 12 months, PSA at recurrence < or > 1.10 ng/m and PSMA staging were not significantly associated with DFS. After relapse, 30 patients (44.1%) received a second SBRT course +/- ADT, 5 patients (7.3%) received prostate bed radiotherapy +/-ADT, 6 patients (8.8%) received ADT alone and 2 patients (2.9%) received ADT+anti androgen therapy. Conclusion Nodal SBRT yielded encouraging DFS and ADT-free survival in this population. Despite the high rate of recurrences, only a minority of patients developed prostate bed recurrence, suggesting that local treatment may be safely avoided. Considering the high percentage of patients managed with a second SBRT course or developing distant metastases, upfront pelvic prophilactic treatment could be considered unnecessary in this population. In order to maximize benefit of this approach in pelvic nodal relapse setting, reliable selection criteria are needed. Interestingly, early detection of nodal relapse with PSMA staging did not seem to influence outcome in this setting. PO-1367 Hypofractionated radiotherapy in prostate cancer older than 70 years M.D.C. Salas Buzon 1 , C. Muñóz Higueras 2 , R. Rodríguez Sánchez 1 , S. Sayago Gil 1 , J. Alcantara Muñóz 3 1 Puerta del Mar University Hospital, Comprehensive Care Department Cancer, Radiation Oncology Service, Cadiz, Spain; 2 Puerta del Mar, University Hospital, Comprehensive Care Department Cancer, Radiation Oncology Service, Cadiz, Spain; 3 Puerta del Mar University Hospital, Comprehensive Care Department Cancer, Radiation Oncology Service, Cádiz, Spain Purpose or Objective Prostate cancer (PC) mainly affects men older than 70 years. The initial radical treatment indicated in this age subgroup is usually external radiotherapy with modern techniques such as Intensity Modulated Radiotherapy (IMRT) and Image Guided Radiation (IGRT) as the best option over surgery. The hypofractionation in 20 fractions has been proven effective and safe. We report our experience about feasibility and toxicity of a intense hypofractionation (Hypo-20) in this patient subgroup. Materials and Methods Between April 2017 and July 2019, 85 men with PC (T1c-T3a), prostate-specic antigen [PSA] 4-26 ng/dL, or gleason score [GS] 6-9, received hypofractionated treatment with 3 Gy daily fractions to a total dose of either 60 Gy in 20 fractions in 4,0 weeks, and IGRT with fiducials. 55 % of patients received short androgen deprivation (AD), 7% long AD and 37.6% without AD. The administered dose was 60 Gy at least 98% the Planning Target Volume (PTV) in 20 fractions/3Gy/day/BEDα/β2,4=187Gy/Eqd2Gy=80Gy, with IMRT and IGRT (6 Mv). Daily image guidance with electronic portal device (EPID) and fiducials (100% patients). PTV was defined as prostate ± seminals vesicles (ssvv) ± pelvic nodes with 5-7-mm. Constraints: rectum V60<10%, V40<50%; bladder V60<25%, V55<40%. Gastrointestinal (GI) and genitourinary (GU) toxicity were prospectively assessed by common terminology criteria for adverse event v5.0 (CTCAE v5.0). Results All patients completed the planned treatment. Median follow-up was 36 months (range 18-45). Median age was 70 years (range 55-79); 32% had low risk , 28% intermediate, 29% high and 12% very high risk. The PSA median before treatment was 8 ng/ml, the PSA median one month after treatment was 0,190 ng/ml and 24 month after radiotherapy was 0,165 ng/ml. There was acute GU toxicity, item frequency Grade 1 in 67% (57 patients), G2 in 19% (16p), and G3 2%(2 p). There was acute GI toxicity, item rectitis G1 in 35%(30 patients), G2 in 2(2%), and G3 3(4%) patients. There were no Grade 4-5 late GU and GI events. One patient developed biochemical failure; no patient developed metastases, 2 patients live with other tumors (bladder cancer and small cell lung cancer) and 2 died from other non-tumor causes. Conclusion In men older than 70 years with prostate cancer, treated with hipofractionated radiotherapy scheme: Hypo- 20, there is a slight increase in mild acute genitourinary toxicity G1-G2, with similar G3 toxicity and similar acute gastrointestinal toxicity G1-G2, compared to other longer schedules. Without no late GU or GI toxicity G4. This slight increase in acute GU toxicity is compensated by the shortening of the length of treatment.

PO-1368 What is clinically important in the pathology specimen for radical radiotherapy in prostate cancer?