Helical tomotherapy (HT) is a novel technique to deliver intensity modulated radiation therapy guided by 3D megavoltage CT imaging. The purpose of our study is to assess the dosimetric parameters related to HT and 3DCRT in advanced non-small cell lung cancer (NSCLC). Eleven patients from the London Regional Cancer Centre and the Cross Cancer Institute with NSCLC underwent individualized treatment planning on both HT and 3DCRT. Corresponding HT and 3DCRT plans for each patient were analyzed using dose-volume histograms for GTV, PTV (median dose 60Gy/30 fractions), and critical structures (lung V5-30, esophageal V50-60, and spinal cord D1). Observed differences in tumor and normal tissue dosimetry were assessed for statistical significance using paired t-tests. A statistically significant improvement on GTV homogeneity but not PTV homogeneity was found in relation with HT. 3DCRT was associated with improved V5 (14%, p = 0.02), V10 (9%, p = 0.04) and V15 (6%, p = 0.04). However, there was no difference in V20 (2%, p = NS); while HT demonstrated superior V30 (5%, p = 0.002). HT achieved excellent tumor coverage relative to 3DCRT in the setting of routinely clinically planned radiation therapy with improvements in the V30 lung parameter. This was at the expense of a modest increase in V5-V15 total lung dose.