This study evaluates the impact of target delineation on the dosimetric outcomes and therapeutic efficacy of iodine-125 seed implantation in the treatment of non-small cell lung cancer. A retrospective analysis was conducted on 31 patients who underwent iodine-125 seed implantation at our center. Post-operative dosimetric parameters, including target volume (Vol), minimum peripheral dose received by 90% of the target Vol (D₉₀), as well as the percentage of target Vol covered by 100% (V₁₀₀), 150% (V₁₅₀), and 200% (V₂₀₀) of the prescription dose, were recorded. Patients were divided into two groups based on treatment response: Group A (complete remission [CR]) and Group B (non-CR group). In addition, the gross target Vol (GTV) of both groups was expanded by 5 mm (clinical target volume [CTV]_5mm) and 1 cm (CTV_1mm), and the corresponding dosimetric parameters were obtained. The independent sample t-tests were used to assess differences between the two groups. All patients successfully completed surgery; among them, 15 achieved CR, 12 had partial response, three had stable disease, and one experienced disease progression. Intraoperative complications included pneumothorax (32%), with three cases (10%) requiring pleural drainage, and intrapulmonary hemorrhage (42%), including hemoptysis (13%), all of which recovered after hemostatic treatment. No other adverse reactions occurred. Statistical analysis revealed no significant difference in dosimetric parameters between the two groups immediately after surgery. However, for CTV_5mm, D₉₀ was significantly lower than its immediate post-operative value (p=0.03, <0.05), whereas the other parameters were not significantly different. Expanding the GTV by 5 mm to define the CTV improves treatment outcomes and may enhance local tumor control.