Distribution of FDG-avid nodes in esophageal cancer: Implications for radiotherapy target delineation.

Abstract

151 Background: Clinical target volumes (CTV) for radiation therapy (RT) in esophageal cancer (EC) are based on standard expansions of the primary tumor volume. Data is needed to better define the regions at highest risk for occult disease, based on histology and location of the primary tumor. We therefore reviewed PET scans in EC patients to characterize the frequency and location of FDG-avid lymph node metastases (LNM). Methods: We identified 474 EC patients with reviewable pre-treatment PET-CT scans who received RT. Tumors were classified by histology and location: upper esophageal (above carina, 15%), or lower/GE junction (85%). Locations of suspicious LNM were classified using standard radiographic nodal atlases, and distances from primary tumor to paraesophageal LNM were also measured. Results: FDG-avid LNM were identified and characterized in 204 patients. The most common LNM in upper EC were supraclavicular (1), retrotracheal (3P) and paratracheal (4). The most common LNM in lower EC were paraesophageal (8), and those in the gastrohepatic space (abdominal stations 1, 3 and 7). Overall, 55% of paraesophageal LNM were adjacent to the primary tumor. Of upper esophageal tumors with paraesophageal LNM, 87% were adjacent to the tumor and none were >6cm from tumor. However, 57% of lower esophageal tumors with paraesophageal LNM had non-adjacent paraesophageal nodes, half of which were >5cm from the tumor. Conclusions: A more data-driven and individualized approach to CTV delineation could improve the therapeutic ratio of RT in esophageal cancer. These results can guide CTV delineation by indicating the potential distribution of nodal involvement in esophageal cancer according to tumor location and histology. Because most paraesophageal LNM are adjacent to primary tumor, the necessity for uniformly large, longitudinal CTV expansions along the esophagus is unclear. [Table: see text]