Long-term Outcomes of Six-Fraction Stereotactic Ablative Radiotherapy to Limited Lymph Node Metastases: An Institutional Case Series

Abstract

Lymph node (LN) metastasis is one of the most common sites to develop disease recurrence or progression after initial cancer treatment. Aggressive local treatment such as surgery or radiotherapy might benefit selected patients with limited metastatic LN(s). Stereotactic ablative radiotherapy (SABR) has been shown to achieve high local control rates with limited toxicities, yet the efficacy and patterns of failure have not been well studied with long-term follow-up. Herein, we report institutional outcomes of patients receiving six-fraction-SABR to involved metastatic LN(s). Since 2012, patients with oligo-metastatic or oligo-progressive LN(s) referred for radical radiotherapy and underwent six-fraction SABR were enrolled for retrospective chart and image review. Response was assessed by RECIST 1.1. Failure patterns and toxicities were recorded. Progression-free survival and overall survival (OS) were estimated by Kaplan-Meier method and log-rank test was used for analysis of prognostic factors. Forty-two patients with forty-six irradiation nodal sites were treated with SABR in this retrospective study. The majority (23/42) were lung cancer patients and the most frequent treatment sites were mediastinum and hilum (26/46). The median SABR dose was 45 Gy (range 30-45 Gy). Only one patient experienced grade 3 gastrointestinal toxicity. With the median follow-up of 52.8 months, median OS is 26.7 months (range 3.3–73.9 months). In-field failure rate is less than 5% (n = 2), and five patients (10.9%) developed isolated recurrences at elective regional lymphatics. The One-year and two-year cumulative isolated regional failure rates are 8.7% and 10.9%, respectively. Patients received >40 Gy (BED10 66.6 Gy) had a significant superior OS compared to those treated with <40 Gy (median OS: 33.6 months versus 10.0 months, log-rank test p = 0.01). Radical treatment of oligo-metastatic or oligo-progressive involved LN(s) with SABR in six fractions seems to provide high local control rate with low-risk of treatment-related toxicities and is not associated with excessive recurrence rates at elective nodal regions after long-term follow-up. A prospective phase II trial to further evaluate the efficacy, safety and patterns of failure for SABR in limited LN metastases was ongoing. Table Failure Sites after LN(s) SABR (N = 46)Abstract 2418; TableVariableNumberWithin RT field2 (4.3%)Isolated elective field5 (10.9%)Distant field35 (76.1%) Open table in a new tab