ESTRO 2023 - Abstract Book

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ESTRO 2023

This multicentric retrospective analysis evaluates the feasibility and efficacy of PC re-irradiation, using a 0.35 T MR Linac.

Materials and Methods Patients affected by local recurrences of PC and treated in five european institutions between 2019 and 2022 were retrospectively collected. All patients had undergone a previous long course Radiation Therapy (RT) in definitive or adjuvant setting. Re-treatment MRgSBRT was delivered with a total dose ranging from 25 to 40 Gy in 5 fractions. Acute and late toxicity were scored according to CTCAE v 5.0 and treatment response was assessed at the end of the treatment and during follow-up visits. Results Eighteen patients were included in the analysis. All the patients had previously undergone External Beams Radiation Therapy (EBRT) with dose ranging from 59.36 to 80 Gy. SBRT re-treatment planning and delivery were performed on hybrid 0.35 T MRI images. Median cumulative Biologically Effective Dose (BED) of SBRT re-treatment was 213,3 Gy (103,1-560), considering an α / β of 1.5. Median FUP time was 4 months (range 2-30). Complete response was achieved in 4 patients (22.2%). No grade ≥ 2 acute genitourinary (GU) toxicity events were recorded, while gastrointestinal (GI) acute toxicity events occurred in 4 patients (22.2%). Table 1 summarizes 1-year and 2-years percentage for investigated clinical outcomes, Table 2 summarizes acute and late toxicity rates.

Conclusion This experience encourages to consider MRgSBRT as a valid therapeutic approach for the treatment of clinically relapsed PC. The accurate identification of the target volumes provided by the higher soft tissue contrast of MRI treatment images and the automatic gating delivery allow to safely deliver high doses to the target, reaching promising outcomes.

PO-1498 Stereotactic re-RT for local recurrence of PCa after primary surgery and RT: a retrospective study.

C. Lorubbio 1,2 , I. Repetti 1,2 , G. Marvaso 1,2 , G. Corrao 1,2 , M. Pepa 1 , M. Zaffaroni 1 , M.G. Vincini 1 , D. Zerini 1 , C. Fodor 1 , G. Musi 2,3 , G. Petralia 2,4 , O. De Cobelli 2,3 , F. Cattani 5 , R. Orecchia 6 , B.A. Jereczek-Fossa 1,2 1 IEO, European Institute of Oncology, IRCCS, Division of Radiation Oncology, Milan, Italy; 2 University of Milan, Department of Oncology and Hemato-Oncology, Milan, Italy; 3 IEO, European Institute of Oncology, IRCCS, Division of Urology, Milan, Italy; 4 IEO, European Institute of Oncology, IRCCS, Precision Imaging and Research Unit, Department of Medical Imaging and Radiation Sciences, Milan, Italy; 5 IEO, European Institute of Oncology, IRCCS, Unit of Medical Physics, Milan, Italy; 6 IEO, European Institute of Oncology, IRCCS, Scientific Directorate, Milan, Italy Purpose or Objective Re-irradiation by stereotactic body radiotherapy (SBRT) represents a valid option for treating locally recurrent prostate cancer (PCa). The aim of this retrospective study was to determine the efficacy and safety of such treatment. Materials and Methods The study included patients who underwent salvage radiotherapy for isolated PCa local recurrence after primary surgery and previous salvage/adjuvant radiotherapy or brachytherapy at our Institution between 2010 and 2021. Patients who received hormone therapy and those who underwent more than one local re-irradiation were also included. Local relapse in the prostate bed was assessed by MRI and/or choline or PSMA-PET. Histological confirmation was not mandatory. Salvage SBRT re-irradiation was delivered with image-guided radiation therapy (IGRT) using the BrainLab VERO System. Results Forty-five patients met the inclusion criteria and were included in the study. Patients and treatment characteristics are listed in Table 1 . Most lesions (29 out of 45, 64.4%) were peri-anastomotic. PET was available for 25 (55.5%) and MRI for 39 (86.7%) patients. Five patients (11.1%) received more than one SBRT treatments for prostate bed recurrence, with one of