Determining optimal clinical target volume margins on the basis of microscopic extracapsular extension of metastatic nodes in patients with non–small-cell lung cancer

Purpose: To determine the optimal clinical target volume (CTV) margins around the nodal gross tumor volume (GTV) in non–small-cell lung cancer (NSCLC) patients by assessing microscopic tumor extension beyond regional lymph node capsules. Methods and Materials: The incidence of nodal extracapsular extension (ECE) and relationship with nodal size were reviewed in 243 patients. Histologic sections of dissected regional lymph nodes up to 30 mm in size were examined to measure the extent of microscopic ECE. We determined the distribution of cases according to extent of ECE and the relationships between ECE extent and lymph node size, regional nodal disease extent, histologic type, and degree of differentiation. Results: The nodal ECE was seen in 41.6% of patients (101/243) and 33.4% of lymph nodes (214/640), and the incidence correlated to larger lymph node size positively. The extent of ECE was 0.7 mm in mean (range, 0–12.0 mm) and ≤3 mm in 95% of the nodes. Positive correlations were found between extent of ECE and larger lymph node size (≥20 mm vs. 10–19 mm or