Stereotactic body radiation therapy for the re-irradiation of local relapse from prostate cancer: results in terms of outcomes and toxicity

Abstract

BACKGROUND: The aim is to retrospectively evaluate toxicity and outcomes of re-irradiation (re-RT) for macroscopic local relapse in patients with prostate cancer (PCa) treated with previous definitive or postoperative radiotherapy (RT). METHODS: Thirty-six patients affected by local relapse after previous definitive or post-operative RT were treated with re-RT in our institute. Treatment dose was 25-30 Gy in 5 fractions. Gastrointestinal (GI) and genitourinary (GU) toxicity was reported according to Common Terminology Criteria for Adverse Events score version 5. Endpoints were Biochemical Relapse Free Survival (BRFS) and Distant Metastases Free Survival (DMFS), assessed with Kaplan-Meier analysis. Univariate and multivariate Cox regression was carried out to evaluate the association between clinical factors and survival outcomes. RESULTS: Twenty-six patients received re-RT after definitive RT and 10 after post-operative RT. At time of re-RT median PSA was 2.57 ng/mL (range 0.23-13.10) and local relapse was detected with choline-Prostate Specific Membrane Antigen (PSMA) – Positron Emission Tomography (PET) or magnetic resonance imagig (MRI) in 18, 17 and one, respectively. Median Clinical Target Volume (CTV) was 17.8 cc (range 1-93.1). In 39% of patients the target corresponds to macroscopic relapse, while in 61% target was the whole prostate or prostate bed. Median follow-up was 28.2 months. No late >2 side effects were collected. Only one patient experienced GI toxicity (G2), while GU side effects were observed in eight patients (six G1 and two G2). Median BRFS survival was 19.0 months, with 1- and 2-year BRFS rates of 63.5% (95% CI 42.5-78.6) and 37.0% (95% CI 17.5-56.8), respectively. At univariate analysis, PSA value at time of re-RT was a predictive factor for BRFS (HR 1.43, 95% CI 1.19-1.73; P=0.000). DMFS rates at 1 and 2 years were 88.0% (95% CI 66.8-96.0) and 72.4% (95% CI 48.1-86.8), respectively. Median DMFS was 19.6 months in with re-RT of the relapsing nodule, while was not reached in patients treated on the whole prostate gland or surgical bed. At univariate analysis, irradiation of the macroscopic relapse vs the whole gland/bed (HR 5.91, 95% CI 1.35-25.80; P=0.018) and increasing PSA at time of re-RT (HR 1.20, 95% CI 1.01-1.41; P=0.030) were negative predictive factors. At multivariate analysis, treatment of the macroscopic relapse only remained an independent predictive factor of distant metastases free survival (DMFS) (HR 4.48, 95% CI 1.09-18.37; P=0.037). CONCLUSIONS: Re-RT in patients treated previously with definitive or postoperative RT was safe and showed promising results in terms of toxicity and biochemical outcomes.