ESTRO 2023 - Abstract Book

S1241

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ESTRO 2023

1 University Hospital Center Mother Teresa, Oncology, Tirana, Albania; 2 University Hospital Center Mother Teresa, Urology, Tirana, Albania; 3 Catholic Hospital " Nostra Signora Del Buon Consiglio", Radiology, Tirana, Albania; 4 Fier Regional Hospital, Oncology, Fier, Albania Purpose or Objective Bladder cancer is common in patients over 65 years old. Patients with potentially curable muscle invasive bladder cancer (MIBC) who are unfit for surgery or trimodal treatment may be evaluated for hypo-fractionated radiation therapy (RT), as a potential curative treatment solution. The aim of our study was to evaluate the efficacy and toxicity of hypofractionated RT in MIBC, in elderly patients unfit for surgery or chemoradiation therapy. Materials and Methods We retrospectively analyzed the data of 16 patients with confirmed nonmetastatic muscle-invasive carcinoma of the bladder, stage T2-T4aN0M0, who underwent transurethral resection of bladder cancer, and were treated with hypofractionated RT alone in our department from September 2018- October 2021. Patients’s Karnofsky Performance State was ≥ 60% and comorbidity was assessed by Charlson Comorbidity Index. Computed tomography imaging and cystoscopy and were used to evaluate treatment outcome. Results Sixteen patients with mean age 78,7 years (range: 72-89 years) and Charlson Comorbidity Index ≥ 5 were analyzed. Male to female rate was 6:1. Pre-treatment staging was T3-T4N0 in 75% of patients and 41% had hydronephrosis. Nine patients (56%) had an uncomplete transurethral resection. 81% percent of the patients were treated with 3D Conformal Radiotherapy (3DCRT) and 19% with Intensity Modulated Radiation Therapy (IMRT). Patients were irradiated with 52.5-55 Gy in 20 fractions to the bladder only. All treatments were completed without interruption. The median follow-up time was 25 months (range:3-36 months). Acute gastrointestinal (GI) grade 2 and grade 3 toxicities occurred in 25% and 9%, respectively.The rate of acute genitourinary (GU) grade 2 and 3 toxicity were 35% and 25%. None of the patients developed GI and GU grade 4 acute toxicity. No statistically significant correlation was found between the radiotherapy technique and toxicity profile. Local control was achieved in 58% of the patients. Recurrent or progressive disease occurred in 24% of the patients. Overall survival at 1 year and 2 year was 83% and 58%, respectively. At the last follow up, 73% of the surviving patients had a functioning bladder. Conclusion Hypofractionation RT alone is a feasible, well tolerated and provides a good local control in elderly unfit patients for trimodal treatment achieving high biological effective dose with a minimal severe acute toxicity profile 1 Institut cancerologique de l'ouest, 44805, Saint Herblain, France; 2 Institut cancerologique de l'ouest, 44805, Saint herblain, France; 3 Institut cancerologique de l'ouest, 44805, saint herblain, France; 4 CHU breast, 29200, Brest, France; 5 chu rouen, 76100, rouen, France; 6 Institut cancerologique de l ouest, 44805, saint herblain, France; 7 institut cancerologique de l'ouest, 44805, saint herblain, France Purpose or Objective Current management for prostate cancer (PCa) relapse in irradiated prostate bed is based on palliative androgen deprivation therapy (ADT). Recently, stereotactic radiotherapy (SBRT) has been developed in this situation. Otherwise, data showed interaction between metformin and radiotherapy (9). We propose a phase I/II study of SBRT reirradiation for relapses in prostate bed, potentiated by metformin. We report phase 1 preliminary results. Materials and Methods We prospectively included patients with biochemical recurrence of PCa occurring at least 2 years after radiation therapy of prostate bed and ADT. Patient should have isolated local recurrence, visible on MRI and PET (Choline or PSMA), and PSA doubling time >6 months.Patient with grade ≥ 2 late post-radiotherapy gastro-urinary toxicity were excluded. Phase I will evaluate SBRT at 5x6Gy, every other day, then according to tolerance, 6x6Gy or5x5Gy. A dummy-run was performed and treatment plan of the first patient of each center was prospectively validated. Metformin is administered during 12 weeks. Patients were followed up weekly during SBRT and after every 4 weeks. Toxicities (SAEs) were graded according to the CTCAE 5.0. The phase I primary objective is the selection of the recommended dose for salvage-SBRT (5 × 6, 6 × 6 or 5 × 5Gy) based on dose-limiting toxicity (DLT), using a time-to-event continual reassessment method based on DLT. DLT is a grade ≥ 3 gastrointestinal or urinary toxicity or any other grade ≥ 4 adverse event that occurs during the 12 weeks following the start of SBRT. Results From November 2020 to November 2021, 6 patients were treated by SBRT and metformin in 2 medical centers. According to the D’Amico classification, 2 patients were at intermediate risk (33%), and 3 were at high risk (50%) (data missing for 1 patient). The median dose delivered to prostatic bed was of 66Gy (range, 60-74) and pelvic node irradiation was delivered in 1 patient. ADT was associated with radiotherapy in 1 patient. Median time since first radiotherapy was 8.3 years (range, 3.4-13.3). Median PSA at recurrence was 1.13 ng/mL (range, 0.18-2.62). Three patients were treated at 1st step 5x6 Gy, and due to the absence of DLT, the following 3 patients were treated at 2nd step 6x6 Gy. All patients received full dose of Metformin. In step 5x6Gy, there were 7 AEs. Toxicities due to SBRT were 2 diarrheas grade 1, 1 diarrhea grade 2, 1 fecal incontinence grade 1, 2 urinary incontinences grade 1, 1 hematuria grade 1, 1 pollakiuria grade 1. No Metformin-related AEs were observed. At step 6x6Gy, there were 5 AEs. Toxicities due to SBRT were 1 grade 1 diarrhea and 1 grade 1 urinary incontinence. Toxicities due to Metformin were 3 grade 1 diarrhea. No SAE, DLT or grade ≥ 3 toxicity were observed. At 6 month follow-up 5 patients (83%) had a biochemical response. PO-1527 REPAIR-GETUG P16: stereotactic reirradiation with metformin for relapse in irradiated prostate bed V. guimas 1 , S. Supiot 1 , E. rio 2 , S. chiavassa 3 , A. blanc lapierre 3 , U. schick 4 , M. roge 5 , L. vaugier 6 , T. perennec 7