Purpose/Objective(s): Stereotactic ablative radiotherapy (SABR) for the treatment of oligometastases is being investigated in ongoing prospective studies, with available phase II data suggesting favorable outcomes. However, there is little data regarding the use of SABR for oligometastatic lymph nodes (LNs). The objectives of the study are to report the demographics, toxicity and outcomes of all patients treated provincially with SABR to oligometastatic LNs. Materials/Methods: We conducted an analysis of all patients who underwent SABR to oligometastatic LNs in our provincial program, from 2013 to 2017. Some of the patients were treated on clinical trials, and data was prospectively collected. For the remaining majority of the patients, baseline patient, tumor, treatment and clinical outcome data were collected through retrospective review. Local control (LC), progression-free survival (PFS) and overall survival (OS) were analyzed by Kaplan-Meier method. Cox regression analysis was used to identify predictors of outcomes. Results: Twenty-four patients underwent SABR to 35 LNs (median 1 and mean 1.5 LNs per patient). The primary sites were colorectal 8 (22.9%), kidney 6 (17.1%), esophagus 4 (11.4%), gallbladder 4 (11.4%), stomach 3 (8.6%), lung 3 (8.6%), skin 2 (5.7%), pancreas 2 (5.7%), liver 1 (2.9%), duodenum 1 (2.9%), and unknown origin 1 (2.9%). Four (11.4%) LNs were in the neck / supraclavicular regions, 14 (40.0%) in the hilum / mediastinum and 17 (48.6%) in the abdomen / pelvis. All patients had treated and controlled primary sites at the time of SABR. The median follow-up post-SABR was 31.7 months. The SABR dose fractionation ranged between 30-60 Gy in 5-10 fractions, with median BED 10 of 72 Gy (range 41.3-105 Gy). All patients were treated with VMAT technique, with 4DCT and respiratory gating used for motion management in 19 (54.3%) cases. The 1-and 3-year LC were 85.4% and 62.7%. The median PFS was 7.6 months, with 1-year PFS at 25.7% and 3-year at 18.4%. The median OS was 45.0 months, with 1-year OS at 91.3% and 3-year at 55.7%. Thirteen (54.2%) patients initiated systemic therapy after SABR, at a median time for these patients of 10.0 months following completion of SABR. The median systemic therapy-free survival (STFS) for all patients after SABR was 17.8 months. There was no grade 3-5 toxicity as per CTCAE V5 criteria. On multivariate analysis, younger age (pZ0.019) and female gender (pZ0.046) were found to be factors predictive of improved OS. Conclusion: SABR to oligometastatic LNs achieves meaningful STFS, without significant toxicity. While the treatment yields moderate rates of long-term LC, the PFS was limited in this cohort. Further evaluation of patient and tumor selection is warranted.

OBJECTIVE:The aim of this study was to perform dosimetric analysis of radiotherapy (RT) plans with or without elective nodal irradiation (ENI) and estimate whether the increase in mean doses (MDs) in the heart and lungs with ENI may lead to late side effects that may surpass the benefits of treatment. METHODS:The dosimetric analysis of 30 treatment plans was done with or without ENI. The planning and dose-volume histograms were analyzed, and the impact on the mortality of cardiovascular and lung cancer was estimated based on the correlation of the dosimetric data with data from population studies. RESULTS:RT with ENI increased the doses in the lungs and heterogeneity in the plans compared to breast-exclusive RT. When the increase in MDs is correlated with the increase of late side-effect risks, the most important effect of ENI is the increased risk of lung cancer, especially in patients who smoke (average increase in absolute risk=1.38%). The increase in the absolute risk of cardiovascular diseases was below 0.1% in the all the situations analyzed.CONCLUSIONS: ENI increases the heterogeneity and the doses at the lungs. When recommending ENI, the risks and benefits must be taken into account, considering the oncology factors and the plan of each patient. Special attention must be given to patients who smoke as ENI may lead to a significant increase in MD in the lung and the increased risk of radiation-induced lung cancer may surpass the benefits from this treatment.