Assessing the role of Stereotactic Body Radiation Therapy in a large cohort of patients with lymph node oligometastases: Does it affect systemic treatment's intensification?

Background and purpose: Lymph nodes (LN) are common site of oligometastases and stereotactic body radiation therapy (SBRT) represents an effective ablative treatment. Aim of this study was to analyze a large cohort of nodal oligometastases treated with SBRT to identify impact on systemic therapy intensification, pattern of recurrence, and predictive factors.

Materials and methods: We included patients with a maximum of 5 oligometastases. Concomitant treatments were allowed. Patients were treated with Volumetric Modulated Arc Therapy (VMAT) and end points were local control of treated metastases (LC), locoregional nodal control (LRNC), distant nodal control (DNC), distant metastases free survival (DMFS), overall survival (OS) and freedom from treatment intensification (FFTI).

Results: 418 LN were treated in 278 patients with 327 SBRT treatments. Patients were more commonly affected by colorectal (20.9%) and prostate cancer (17.99%). Most represented schedule was 45 Gy in 6 fractions, with a median BED10 of 78.75 Gy. After median follow-up of 15.1 months, LC at 1 and 2 years were 87.2% and 76.8%, respectively. Prostate primary tumor, small volume, oligorecurrence, and BED10 ≥75 Gy were associated with higher LC. One and 2 years FFTI were 82.8% and 74.5%; in patients reporting intensification of systemic therapy, median time was 8.43 months, while for patients who repeated SBRT, median FFTI was 14.6 months. Rates of LRNC at 1 and 2 years were 70.9% and 57.6%, and DNC were 82.0% and 77.9%.

Conclusion: With the present analysis, we confirmed on a large cohort the benefit from SBRT on lymph node oligometastases in multidisciplinary management. Combination of SBRT with new systemic therapies, including immunotherapy and targeted therapy, should be investigated to reduce the risk of progression out of the field of irradiation.