Three-dimensional conformal radiation may deliver considerable dose of incidental nodal irradiation in patients with early stage node-negative non-small cell lung cancer when the tumor is large and centrally located

Background and purpose: To determine the dose to regional nodal stations in patients with T_1-3N₀M₀ non-small cell lung cancer (NSCLC) treated with three-dimensional conformal radiation therapy (3DCRT) without intentional elective nodal irradiation (ENI). Materials and methods: Twenty-three patients with medically inoperable T_1-3N₀M₀ NSCLC were treated with 3DCRT without ENI. Hilar and mediastinal nodal regions were contoured on planning CT. The prescription dose was normalized to 70 Gy. Equivalent uniform dose (EUD) and other dosimetric parameters (e.g., V₄₀) were calculated for each nodal station. Results: The median EUD for the whole group ranged from 0.4 to 4.4 Gy for all elective nodal regions. Gross tumor volume (GTV) and the relationship between GTV and hilum were significantly correlated with irradiation dose to ipsilateral hilar nodal regions (P < .05). For patients with GTV ≥ 30.2 cm³ (diameter ≈ 4 cm) and or having any overlap with hilum, the median EUDs were 9.6, 22.6, and 62.9 Gy for ipsilateral lower paratracheal, subcarinal, and ipsilateral hilar regions, respectively. The corresponding median V₄₀ were 32.5%, 39.3%, and 97.6%, respectively. Conclusions: Although incidental nodal irradiation dose is low in the whole group, the dose to high-risk nodal regions is considerable in patients with T_1-3N₀ NSCLC when the primary is large and/or centrally located.