Stereotactic Body Radiotherapy of Lymph Node Oligometastases

The aim of this retrospective study is to evaluate the efficacy and toxicity of extracranial stereotactic radiotherapy for the treatment of oligometastatic lymph node involvement in the mediastinum, retroperitoneum, and pelvis in a consecutive group of patients from real clinical practice.

Of a total of 50 patients treated between 2011 and 2017, 29 were men and 21 were women, and the mean age was 62 years (median 66 years, range 25-81 years). Patients were most often irradiated in five fractions; the dose was selected according to dose-volume histograms of organs-at-risk in proximity to the planning target volume. The primary objectives were local control (LC), progression-free survival (PFS), time to multiple dissemination not allowing the use of local treatment methods (freedom from widepread dissemination - FFWD), and overall survival (OS). Acute and delayed toxicity were evaluated as well.

The median dose equivalent at α/β = 10 (BED10) was 54 Gy (range 48-80 Gy). The median follow-up period was 40.4 months. LC after irradiation was 90% in 1 year and 75% in 3 years. Median time to local progression was not achieved. Patients irradiated with a high dose had significantly better LC than patients irradiated with a low dose; the cut-off was the median of the applied dose (ie BED10 = 54 Gy). Pathological node localization had no significant effect on LC. The median PFS was 8.2 months (95% CI 7.4-11.6 months). PFS in 1 year was 38.5% and 17% in 3 years. The median OS was 37.3 months (95% CI 23.2-51.4 months). One-year OS was 83% and 3-year OS was 51%. The median FFWD was 13.6 months (range 8.7-18.5 months). The one-year FFWD was 55% and the 3-year FFWD was 24%. None of these parameters (PFS, OS, FFWD) was dose or localization dependent. No grade III or IV toxicity was reported.

Our study shows that targeted stereotactic radiotherapy is a very effective low toxic treatment for oligometastatic lymph node involvement. It can delay cytotoxic chemotherapy and thus improve/maintain the quality of life of patients. Approximately one fifth of patients treated with extracranial stereotactic radiotherapy for oligometastatic lymph node involvement survived without signs of disease for prolonged periods. Future studies should aim at identifying patients who would benefit most from this treatment, adjusting the timing of extracranial stereotactic radiotherapy depending on the treatment strategy, and optimizing the dose prescription. This work was supported by grant of the Ministry of Health of the Czech Republic AZV 19-00354 and by grant of the Ministry of Health of the Czech Republic - Conceptual development of a research organization (MMCI 00209805). The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers.