ESTRO 2023 - Abstract Book

S447

Sunday 14 May 2023

ESTRO 2023

(TURBT). The target delineation was guided by either intravesical injection of Lipiodol or through fusion of the pre treatment imaging to the planning CT. The majority of cases were treated with daily image-guided IMRT/VMAT. Kaplan Meier was used to characterize overall survival (OS) and progression-free survival (PFS). Cumulative incidence function (CIF) was used to estimate local (intravesical) recurrence (LR), regional recurrence (RR) and distant metastasis (DM). Univariable and multivariable cause-specific hazard model was used to assess factors associated with LR. Results The median age was 73 years (range 43, 95). The median EQD2 to the boost volume was 66Gy (range 52.1, 70). Lipiodol injection was used in 64 patients (55%), all treated with IMRT/VMAT. 95 (81%) received concurrent chemotherapy along with the RT, of whom, 44 (38%) received neoadjuvant chemotherapy. The median follow-up was 37 months (IQR 16.2, 83.3). At 5-year, OS and PFS were 79% (70.5-89.2) and 46% (36.5-57.5), respectively. Forty-five patients had bladder relapse, and the CIF of LR at 5-year was 44% (33.5- 54.5), of which 30 of the 45 patients with LR (67%) were at site of the tumor bed. Nine patients underwent salvage-cystectomy. Neoadjuvant chemotherapy was a significant predictor factor for lower incidence of LR, in both univariate and multivariable analysis [HR (95% CI) 1.98 (1.01, 3.87); p=0.046 and 2.11 (1.01, 4.42); p=0.047, respectively]. Late high-grade (G3-G4) genitourinary and gastrointestinal toxicity were 3% and 1%. Conclusion Partial boost RT technique in MIBC is associated with good local disease control and high rates of cystectomy free survival. We observed a pattern of predominantly local failure in the tumor bed, supporting the use of a dose-painted approach/de escalation strategy to the uninvolved bladder. Prospective trials are required to compare oncological and toxicity outcomes between dose-painted and homogeneous bladder RT techniques. PD-0566 MRI before salvage radiotherapy after radical prostatectomy in prostate cancer: a case-control study L. Cavallini 1 , C. Gaudiano 2 , E. Galietta 1 , F. Mammini 1 , S. Paolinelli 1 , V. Laghi 1 , D. Vallerossa 1 , E. Natoli 1 , A.G. Morganti 1 , A. Arcelli 3 , S. Cammelli 1 , G. Macchia 4 , F. Deodato 5 , R. Golfieri 6 , G.P. Frezza 7 , M. Ntreta 3 1 Radiation Oncology, Department of Experimental, Diagnostic and Specialty Medicine-DIMES, Alma Mater Studiorum University of Bologna, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 2 Department of Radiology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 3 Radiation Oncology, IRCCS Azienda Ospedaliero Universitaria di Bologna, Bologna, Italy; 4 Radiation Oncology Unit, Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Campobasso, Italy; 5 Radiation Oncology Unit, Istituto di Radiologia, Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Università Cattolica del Sacro Cuore, Campobasso, Roma, Italy; 6 Department of Radiology, IRCCS Azienda Ospedaliero-Universitaria, Bologna, Italy; 7 Radiotherapy Department, Ospedale Bellaria, Bologna, Italy Purpose or Objective Current international guidelines recommend choline-PET or PSMA-PET in patients with prostate cancer candidates for salvage radiotherapy (RT) to rule out the presence of lymph node or hematogenous metastases prior to RT. However, in our centers, we tested the use of pelvic MRI in order to evaluate its effectiveness in detecting locoregional relapses and therefore to optimize salvage RT. Therefore, the aim of this analysis is to compare two matched cohorts of patients who underwent or did not undergo MRI before salvage RT in terms of biochemical disease control. Materials and Methods One hundred sixteen patients from three centres were included in this study. Patients in the two cohorts were matched according to: PSA before SRT (<0.2; 0.2-0.5; 0.5-1.0; >1.0 ng/ml), pathological tumor stage, ISUP grade group (1, 2, 3, 4, 5), pelvic nodal irradiation, and adjuvant hormonal therapy. Kaplan-Meier survival curves were compared using the log rank test. This analysis is part of a multicenter observational study (ICAROS trial) approved by the ethics committees of the participating centers. Results Macroscopic locoregional relapse was identified in forty-two/58 patients (72.4%) undergoing pelvic MRI and therefore these patients were treated with a median total dose of 70.4 Gy (range: 66-72.6), while patients without MRI or with negative MRI received a median total dose of 66 Gy (range: 62.5-72.0). Indeed, in patients with MRI-detected relapse, a focal boost (sequential or concomitant) was administered with a median dose of 4.4 Gy (range: 4.4-70.5). Overall, comparing the cohorts of patients who underwent and did not undergo MRI, a significantly higher rate of biochemical relapse-free survival was recorded in the first group (2-year rates: 91.5% versus 73.6%; p = 0.006; Figure 1).