ESTRO 2023 - Abstract Book

S517

Sunday 14 May 2023

ESTRO 2023

Barakaldo, Spain; 6 Genesis Care, San Francisco de Asis and La Milagrosa, Radiation Oncology, Madrid, Spain; 7 Biocruces Bizkaia Health Research Institute, Radiation Oncology , Barakaldo , Spain; 8 Biocruces Bizkaia Health Research Institute, Radiation Oncology, Barakaldo , Spain Purpose or Objective To evaluate the predictive factors for biochemical failure and distant metastases in a prospective cohort of patients with localized prostate cancer treated with the combination of HDR brachytherapy and External Beam Radiotherapy. Second, to analyze the biochemical failure-free (BFFS) and metastases-free survival (MFS) rates at 5 and 7 years of follow-up of patients stratified by risk groups. Materials and Methods Patients with histological confirmation of intermediate (IR) or high-risk (HR)prostate adenocarcinoma were analyzed. Patients without staging MRI and those with pelvic lymph node involvement were excluded from this analysis. The treatment administered consisted of a single fraction of HDR of 15 Gy combined with RT of 37.5 Gy in 15 fractions. Patients with unfavorable IR disease received ADT for 6 mo and patients with HR 24 mo of ADT. Descriptive analyses were performed. Univariate and multivariate Hazard Ratios were obtained from Cox proportional regression models. Finally, the Kaplan Meier model was used to describe the survival of the events of interest. Results 309 patients were treated prospectively (199 were IR and 110 HR). Median age was 72 years (IQR 68 – 75); 58.3% were MRI stage ≤ T2c, 34.1% T3a and 7.6% T3b; ISUP grade was 1-3 in 78.9% and ISUP 4-5 in 21.1%. 71.8% of patients had ≤ 50% positive cores in biopsy and 28.2% had >50%. Median pre-treatment PSA was 9.9 ng/mL. After a median follow-up of 77.8 months (IQR 24.9 – 107.1 months), 41 patients presented a biochemical failure and 17 developed distant metastases. Multivariate cox-regression analyses found that MR-T3b Stage was the only predictive factor (HR 3.88, 95% CI 1.68-8.94, p=0.001) for biochemical failure and the number of positive cores (>50%) the only independent predictive factor of distant metastases (HR 4.36, 95% 1.72-11-1, p= 0.002) In terms of survival, the BFFS rates at 5 and 7 years were 92.5% and 88.1% for patients with intermediate disease and 84.7% and 78.1 for patients with high-risk. MFS rates were 97.3% and 95.1% for intermediate-risk and 88.6% and 83.3% for high-risk disease. Conclusion Combined treatment of HDR BT with EBRT achieves excellent biochemical and metastatic control rates. Patients with multiparametric MRI evidence of invasion of the seminal vesicles and involvement of more than 50% of the cores in the prostate biopsy are patients with a higher risk of presenting a biochemical recurrence or developing metastases due to their prostate cancer. OC-0628 Salvage low-dose-rate brachytherapy for locally recurrent prostate cancer after radiotherapy Y. Meraouna 1 , P. Blanchard 2 , S. Losa 3 , A. Labib 1 , S. Krhili 1 , G. Crehange 1 , T. Flam 4 , J. Cosset 5 , M. Kissel 1 1 Institut Curie, Radiotherapy, Paris, France; 2 Gustave Roussy, Radiotherapy, Villejuif, France; 3 Institut Curie, Physics, Paris, France; 4 Clinique Saint Jean de Dieu, Urology, Paris, France; 5 Centre Charlebourg - La Defense - Amethyst Radiothérapie, Radiotherapy, La Garenne-Colombes, France Purpose or Objective The optimal management of locally recurrent prostate cancer after radiotherapy is still unclear but local salvage treatments are gaining interest. A retrospective, single-institution analysis of clinical outcomes and treatment-related toxicity in patients treated with salvage I-125 low-dose-rate (LDR) brachytherapy (BT) for locally-recurrent prostate cancer after radiotherapy was conducted in a Comprehensive Cancer Center. Materials and Methods A total of 94 patients with an isolated local relapse of prostate cancer after radiotherapy who underwent salvage LDR-BT between 2006 and 2021 were included. Results Median follow-up was 34 months. Initial radiotherapy was external beam radiotherapy in 73 patients (78%) with a median dose of 76 Gy [Q1-Q3: 74-76] and I-125 BT in 21 patients (22%) with a prescribed dose of 145 Gy. Median PSA at salvage brachytherapy was 3.75ng/mL [Q1-Q3: 2.4-5.9] with a median interval between first and salvage irradiation of 9.4 years [Q1-Q3: 6.7-11.7]. Histological proof of local relapse was available for all patients but one. Salvage LDR-BT was administered to either the whole gland (70%) with a dose prescription of 120 Gy for a large majority of the patients; the whole gland with a boost (20%) with a dose prescription of 90 Gy to the whole gland and 145 Gy to an MRI-based GTV; or a partial volume (hemigland or ultrafocal) (9%) with a dose prescription of 120 Gy (or 145 Gy for 1 patient only). It was associated with androgen deprivation therapy for 32% of the patients. Only 4% of the patients were castrate-resistant. Failure free survival (biological and clinical) was 82% and 66% at 2 and 3 years respectively in the whole population. The only factors associated with failure-free survival on multivariate analysis were hormonosensitivity at relapse and European Association of Urology (EAU) prognostic group. Late grade 3 urinary and rectal toxicities occurred in 12% and 1% of the patients respectively.

No significant difference in toxicity or efficacy was observed between the three implant volume groups.