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Stereotactic Body Radiation Therapy (SBRT) is now accepted as a standard of care for medically inoperable early stage non-small cell lung cancer (NSCLC) [1], [2]. Long term results of retrospective series show excellent local control rates but poor survival with higher rates of distant metastasis despite early stage at presentation [3], [4], [5], [6]. Development of a prognostic tool to recognize factors can allow for stratification to test treatment strategies in future trials and selection of risk appropriate treatment strategies. These prognostic factors could be the bridge from empirical to individualized treatments for this patient population. Previous studies have recognized patient, tumor and treatment related factors associated with overall survival (OS) or distant metastases free survival (DMFS) like the age at presentation, tumor size, histology, radiation dose, maximum standardized uptake value (SUVmax) of the primary tumor and various hematologic parameters [7], [8]. Many studies have evaluated the role of absolute leucocyte, neutrophil, monocyte, lymphocyte or platelet count, ratios of various parameters like neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), lymphocyte to monocyte ratio among others and found conflicting results and a variety of threshold values with prognostic importance [9], [10], [11], [12], [13], [14]. However, most of these studies have evaluated patients with advanced stage or medically operable early stage NSCLC who underwent surgery. There are very few studies evaluating their role in stage I NSCLC undergoing SBRT [15], [16]. Most of these studies have limited their blood values measured within the 3 month period prior to initiating therapy [9], [10], [11], [12], [13], [15], [17]. Moreover, none of the studies have evaluated the changes in the values of the hematological parameters between pre-SBRT and post-SBRT. Therefore, in our study we evaluated the role of hematologic and other known prognostic factors including the trends of change in the hematological parameters between pre-SBRT and post-SBRT in early stage NSCLC patients treated with SBRT for various survival end points. We included CBC values that were produced within 6 months prior to and after SBRT in order to evaluate if these values show prognostic significance like that of the values within 3 months in other studies.