The Association Between Radiation to the Immune System and Overall Survival and Disease Progression in Non-Small Cell Lung Cancer Treated With Stereotactic Body Radiation Therapy.

PURPOSE/OBJECTIVE(S) Although the effects of effective radiation dose to the immune cells (EDRIC) in advanced stage non-small cell lung cancer (NSCLC) on overall survival (OS) and progression free survival (PFS) have been studied, no other study has shown its impact in early-stage NSCLC. In this retrospective cohort, we evaluated the role of EDRIC in this population. MATERIALS/METHODS The study cohort was generated using the cancer registry data including patients with early-stage NSCLC (T1-2, N0) who received stereotactic body radiation therapy (SBRT) in our institute since 2007. Patient were excluded if the dosimetric data were not available. EDRIC was calculated as a function of the number of radiation fractions and mean doses to the lung, heart, and the remaining body. Failure was defined as any type of failure including in-field, out-field, nodal and distant metastases. Variables that were included in the univariate and multivariate analysis were age, sex, positron emission tomography (PET) scan at diagnosis, Karnofsky Performance Status (KPS), Charlson Comorbidity Index (CCI), smoking history, histology, tumor location (central versus peripheral), TNM stage, Gross Tumor Volume (GTV) size, BED and EDRIC. RESULTS 148 patients were included. 55% are female with a median age of 73 years. 23% had central lesions. 97% had diagnostic PET scan and all were treated with a mean dose of 50 Gy and Biological Effective Dose (BED) above 100 Gy. With a median follow up of 29 months, 34% of patients developed failure. The 2-year OS was 54%. In multivariate analysis, higher EDRIC (HR: 2.04) and lower KPS (HR: 0.35) continued to be associated with worse OS (P = 0.02 and P = 0.008). Considering each EDRIC quartile, there was a statistically significant difference in OS between 1st and 4th and 1st and 3rd quartile (P = 0.01, P = 0.02). The median OS in each quartile is as followed: not reached, 47, 21, 21 months. There was no association between EDRIC and PFS. However, in multivariate analysis, KPS was associated with any type of failure (HR: 0.12, P = 0.013) CONCLUSION: This study showed that EDRIC can affect OS in patients with early staged NSCLC treated with SBRT. However, it does not affect PFS and any type of failure after receiving SBRT.