Acute Palliation of Intrathoracic Symptoms: No Improvement with Dose-Escalated Hypofractionated External Beam Radiotherapy

Abstract

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.