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Poster: Clinical track: Urology-non-prostate PO-1212: SBRT in patients with oligometastatic renal cell carcinoma in the era of immunotherapy O.C. Güler, P. Hurmuz, B. Tilki, G. Ozyigit, B.A. Yildirim, F. Akyol, C. Onal. [Extracted from the article]

Prospective randomized phase 3 trials have shown that hypofractionated radiotherapy (RT) regimens are safe and effective for definitive prostate RT. There is, however, a scarcity of data describing the outcomes of ultra-hypofractionation in the postoperative setting. The purpose of this study was to assess the safety of ultra-hypofractionated RT to prostate bed using stereotactic body RT (SBRT) technique. The clinical data of 69 prostate cancer patients who received postoperative prostate bed SBRT between August 2018 and September 2020 were reviewed retrospectively. All patients had had radical prostatectomy, and 44 (63.8%) had pelvic lymph node dissection, with a median of 14 (range: 2–34) lymph nodes dissected. The primary endpoints were failure from biochemical failure (FFBF) and acute and late gastrointestinal (GI) and genitourinary (GU) toxicities. Secondary endpoint was progression free survival (PFS). The median age was 64 years (range: 43–76 years). Thirty patients (43.5%) received adjuvant RT and 39 (56.5%) had salvage RT median 12.4 months (range: 1.5–137.6 months) after surgery. Median SBRT fraction and total doses were 7 Gy (range: 6–7.3 Gy) and 30 Gy (30–36.5 Gy), respectively delivered in 5 days. Majority of patients (82.7%) had high risk disease and only 13 patients (18.8%) had lymph node metastasis. Seminal vesicle invasion was observed in 22 patients (31.9%) and 49 patients (71%) had extracapsular invasion. Forty-eight patients (69.6%) had positive surgical margin. Pre-SBRT and post-SBRT PSA values were 0.37 ng/mL and 0.05 ng/mL, respectively. 27 patients (39.1%) also received adjuvant androgen deprivation therapy (ADT) after SBRT and post-treatment PSA nadir value was 0.01 ng/mL. Median follow-up time was 23.8 months (range: 2.8–37.2 months). The 2-year FFBF and PFS were 91.4% and 87%, respectively. Seven patients (10.1%) had BF median 18.5 months (range: 1.7–33.5 months) after completion of SBRT. Disease progression was observed in 10 patients (14.5%) median 13.9 months after treatment. Acute GI and GU system toxicities of grade 2 or greater were observed in 13% and 14.5% of patients, respectively. Late GI and GU toxicities of grade 2 or greater were observed in 4.3% and 16% of patients, respectively. SBRT delivered to the prostate bed over a 5-day period was found to be safe, with acceptable acute and late toxicities. Longer follow-up and randomized trials with a large patient population, however, are required to validate our findings. [ABSTRACT FROM AUTHOR]

Previous studies demonstrated the efficacy of stereotactic-body radiotherapy (SBRT) for oligometastatic renal cell carcinoma (RCC) patients. However, it has not been well-studied in patients with bone-only metastatic RCC. This study aimed to analyze the prognostic factors associated with overall survival (OS) and progression-free survival (PFS) in patients with bone-only metastatic RCC who have five or fewer lesions treated with SBRT. The clinical data of 54 patients with 70 bone metastases undergoing SBRT treated between 2013 and 2020 with a fraction dose of at least 6 Gy per fraction, and a biologically effective dose (BED) of at least 90 Gy was retrospectively evaluated. The prognostic factors associated with OS and PFS were assessed. The majority of lesions were located in the spine (57.4%), and had only one metastasis (64.8%). The median SBRT fraction and total doses were 10 Gy (range: 6–18 Gy) and 20 Gy (range: 12–40 Gy), and SBRT was administered with a median fraction of 3 (range, 1–5). The median BED of SBRT was 108.4 Gy (range: 90.0–202.2 Gy). After a median follow-up of 22.4 months, the 1- and 2-year OS rates were 84.6% and 67.3%, respectively, and median OS was 43.1 months. The 1- and 2-year PFS rate, and median PFS were 63.0%, 38.9%, and 15.3 months, respectively. After completion of metastasis-directed treatment (MDT), disease progression occurred in 26 patients (48.1%) at a median of 12.7 months (IQR 7.1–29.9 months). There were 22 (84.6%) with distant metastasis, one (3.8%) with in-field local recurrence, and three (11.6%) with both distant metastasis and local recurrence. In SBRT-treated lesions, only 4 patients (7.4%) experienced local recurrence, and the 1- and 2-year LC rates per lesion were 94.9% and 92.0% per lesion. Age, metastasis localization, and number of fractions for SBRT were significant prognostic factors for OS in univariate analysis. In multivariate analysis, patients with spine metastasis had a better OS [HR=3.1 (95% CI, 1.3–7.7; p = 0.001)] compared to their counterparts, and patients who received single fraction SBRT [HR=2.2 (95%, 1.2–4.2; p = 0.01)] had a better PFS than those who did not. No patient experienced acute or late toxicities of grade 3 or greater. To the best of our knowledge, this is the first multicenter study of bone-only oligometastatic RCC patients treated with SBRT. Despite excellent LC at the oligometastatic site treated with SBRT, disease progression was observed in nearly half of patients 13 months after MDT, particularly as distant disease progression other than treated lesion, necessitating an effective systemic treatment to improve treatment outcomes. Prospective trials of SBRT for oligometastatic bone sites are warranted because they may shed light on disease control, survival, and quality of life after such therapy. [ABSTRACT FROM AUTHOR]