This retrospective exploratory dosimetric study compared radiotherapy treatment plans utilized under identical optimization constraints using TrueBeam, Halcyon, and Tomotherapy platforms in patients with stage III non-small cell lung cancers (NSCLC). A retrospective analysis was conducted on fifteen patients with histopathologically confirmed NSCLC. For each patient, four treatment plans were generated using Helical tomotherapy (HT), Halcyon-VMAT (h-VMAT), VMAT, and IMRT techniques. Target coverage, conformity index (CI), homogeneity index (HI), D95, monitor units (MU), and treatment time (TT) were analyzed and compared. HT technique achieved significantly superior conformity compared with h-VMAT, VMAT and IMRT (p < 0.001). However, no statistically significant difference was found across the four techniques regarding the HI. The dose delivered to 95% of the PTV (D95) value obtained with VMAT was found to be significantly superior to that obtained with HT (p = 0.018). While the average MU values required for treatment were lowest in the VMAT technique, the highest value was found in the HT technique. The shortest TT was observed with h-VMAT (p < 0.001). The results indicate that HT may be advantageous when high conformity prioritized, whereas h-VMAT may improve treatment efficiency through reduced delivery time. However, these results should be interpreted cautiously given the limited sample size and the use of dose calculation algorithm. This comparison provides clinically relevant insight that may support technique selection according to specific radiotherapy treatment priorities. It should be noted that dose calculations were performed using different algorithms across platforms, which may lead to systematic differences in dose estimation, particularly in low-density lung regions.