SBRT is standard of care for medically inoperable patients with ES-NSCLC and can be delivered using robotic radiosurgery or standard linear accelerator (LINAC) platforms. CK uses hundreds of anterior oblique non-coplanar beams while LINAC SBRT commonly uses volumetric modulated arc therapy (VMAT) with multiple coplanar full or partial arc fields. SBRT plans are designed to cover the PTV in prescription dose while achieving steep dose fall-off in adjacent tissue which causes increased dose heterogeneity “i.e., hotspots” in the target volume. We aimed to compare the dosimetric characteristics of lung SBRT plans delivered at one institution based on CK vs LINAC VMAT technique. Patients were included who received CK-based (2012-16) or LINAC-based SBRT from (2016-17) for T1-2N0M0 NSCLC. SBRT plans of 198 patients who met inclusion criteria were analyzed (CK, n=149 and LINAC, n=59). CK plans were computed using Monte Carlo algorithm, while the LINAC-based VMAT plans were computed in collapsed cone convolution-superposition algorithm. All clinically delivered plans were reviewed to extract dosimetric parameters including target volume coverage and OARs dose distribution. Differences in mean dosimetric values by technique were estimated via Wilcoxon Rank-Sum Test. Multivariate analyses were run using logistical regression to test for confounding variables. LINAC SBRT was prescribed to a higher mean isodose line (IDL) (89% vs 80%, p<.001) yet had increased mean ratios of GTVmax (131% vs 125%, p<.001), GTVmean (120% vs 116%, p<.001), PTVmax (132% vs 126%, p<.001), and D90GTV (114% vs 111%, p<.001) doses to prescription dose compared to CK. LINAC-based SBRT had lower mean conformality index (1.10 vs. 1.21, p <.001) than CK, but there was no difference in mean R50 values (5.06 vs. 4.88, p=.67). Mean ratio of PTV to total lung volume did not differ significantly for LINAC SBRT vs. CK (1.17% vs. 1.54%, p=.08), but LINAC SBRT was associated with lower average lung V5 (18% vs. 25%, p<.001), V10 (11% vs. 14%, p=.02), mean lung dose (3.7 Gy vs. 5.1 Gy, p<.001) and lung volume (cc) receiving <12.5 Gy (3980 cc vs. 3300 cc, p=.002) than CK. LINAC SBRT was also associated with lower heart mean doses compared to CK (1.8 Gy vs. 2.5 Gy, p=.004) and heart V5 (12.7% vs. 19.5%, p=.009). There was no difference in max dose to the proximal bronchial tree. On multivariate analysis controlling for total dose, lung volume, PTV size, and target lobe the differences in lung V5 (p <.001) and mean lung dose (p <.001) by technique persisted but differences in lung cc receiving <12.5 Gy, lung V10, heart V5 and heart mean dose were no longer statistically significant. Despite being prescribed to higher mean IDLs, LINAC SBRT with VMAT technique delivered higher doses to the GTV and PTV as compared to CK and was associated with lower lung V5 and mean lung dose but not lower lung V10 or V20.