Impact of Anatomic Tumor Location on Clinical Outcomes: A Long-Term Analysis of Early Stage Non-Small Cell Lung Cancer Treated with Stereotactic Body Radiation Therapy and Fiducial Tracking

Abstract

Treatment of early stage non-small cell lung cancer (ES-NSCLC) broadly includes surgical resection and definitive radiotherapy. Although surgical resection remains the standard of care for operable patients, approximately 20% of patients are deemed inoperable. A substantial body of literature has established stereotactic body radiation therapy (SBRT) as the ideal definitive therapy for those patients ineligible for surgery. A variety of techniques exist for SBRT delivery in the thorax, each with their own accommodations for respiratory motion. Such motion is linked with the anatomical location of the tumor, with those closer to the diaphragm demonstrating larger excursions than those localized to the upper lobes. In this study, we examined the long-term outcomes of patients treated with robotic SBRT using fiducial tracking to elucidate variations in clinical outcomes as a consequence of tumor anatomical location. This is a single institutional analysis of patients with medically inoperable, biopsy-confirmed lymph-node negative (T1-3N0M0) ES-NSCLC using the AJCC 7th edition Cancer Staging Manual. Patients were treated per institutional protocol with robotic SBRT and fiducial tracking to a total dose of 45-60 Gy in 3 to 5 fractions prescribed to the planning target volume defined as a 5-mm expansion from the gross tumor volume. Estimates of overall survival, progression-free survival, local control, and locoregional control for patients were obtained using Kaplan-Meier analysis. Association with tumor stage, tumor location, histology, age, performance status, smoking history, and biologically equivalent dose were evaluated using Cox proportional hazards regression models. One-hundred medically inoperable patients with early stage NSCLC were treated from August 2005 to August 2017. The median age of all treated patients was 74 (range, 52 – 94). The majority of patients (n = 67) had tumors in the upper lobes. Most patients had T1a (n = 27), T1b (n = 27), or T2a (n = 25) tumors. After a median follow up of 3.3 years, median overall survival for the entire cohort was 50 months. At 3 years, overall survival rates were 62% for patients with upper lobe tumors and 54% for patients with lower lobe tumors (p = 0.10). Progression-free survival (62% v 54%, p = 0.38), local control (89% v 93%, p = 0.66), and locoregional control (83% v 79%, p = 0.98) rates were also similar between the two groups. Anatomical location did not appear to lead to significantly different long-term clinical outcomes. Fiducial tracking appears to work well in this diverse population of patients despite differences in respiratory motion. Future research should explore if difference in SBRT technique can lead to variations in clinical outcomes stratified by tumor anatomical location.