2364 - Impact of Systematic Invasive Mediastinal Staging on Recurrence Rates Following SBRT for Early-Stage NSCLC

Purpose/Objective(s): The purpose of this study is to compare local, regional, and distant recurrence rates of patients with Stage I Non-Small Cell Lung Cancer (NSCLC) undergoing Stereotactic Body Radiation Therapy (SBRT) who received systematic Invasive Mediastinal Staging (IMS), random sampling IMS, or non-invasive mediastinal staging alone via PET/CT. We hypothesize that patients undergoing systematic IMS will exhibit lower local, regional, and distant recurrence rates than those undergoing random sampling IMS or non-invasive staging with PET/CT. The National Comprehensive Cancer Network (NCCN) Guidelines currently state that for medically inoperable patients with Stage I NSCLC, the risk associated with IMS may outweigh the benefit, with data supporting the use of IMS being mixed. Therefore, this study is important in advancing the literature on the impact IMS has on recurrence rates for patients with early-stage NSCLC undergoing SBRT treatment.

Materials/Methods: This retrospective chart review included 209 cT1–2N0 NSCLC patients treated at one of five locations around an urban metro area. Inclusion criteria involved being 18 years or older with cT1–2N0 NSCLC, treatment with definitive SBRT between 2015-2020, and receiving 3–10 fraction regimens with a biologically effective dose of =100 Gy. Patients without a PET/CT performed for initial staging or with no follow-up CT after treatment with SBRT were excluded. Kaplan–Meier survival analysis, log-rank tests, and Cox regression models were utilized for statistical analysis.

Results: Systematic IMS was performed on 103 patients (49.28%), random sampling IMS on 45 patients (21.53%), and PET alone on 61 patients (29.19%). The mean follow-up was 91 months and the median follow-up was 45 months. Systematic IMS was found to have a statistically significant lower rate of local recurrence compared to random sampling IMS (p = 0.006). No statistically significant difference in local recurrence rates was seen between systematic IMS and PET staging. The systematic IMS group had the lowest local recurrence rate (3.88%) compared to random sampling IMS (20.00%) and PET (14.75%). There was no statistically significant difference seen in regional or distant recurrence between the different staging modalities. Regional progression rates were 13.33% (random sampling IMS), 8.20% (PET), and 5.83% (systematic IMS). Distant progression rates were 9.71% (systematic IMS), 8.89% (random sampling IMS), and 8.20% (PET).

Conclusion: Systematic IMS was shown to have lower local recurrence rates following SBRT compared to random sampling IMS, but not statistically different from PET alone. The finding of lower local recurrence rates without a similar improvement in regional or distant control with systematic IMS may be related to the extent of follow-up. The initial findings of this study support further analysis of this cohort at a longer follow-up to determine if local recurrence benefit manifests with improvement in regional and distant control.