3513 - Impact of Elective Nodal Irradiation (ENI) vs. Involved Field Irradiation (IFI) on Estimated Dose Radiation to Immune Cells (EDRIC) and Prognostic Analysis in Esophageal Carcinoma

Purpose/Objective(s): To evaluate the differences in EDRIC between ENI and IFI in patients with esophageal squamous cell carcinoma and analyze their impact on survival, thereby providing evidence for radiotherapy decision-making.

Materials/Methods: A retrospective analysis was performed on 325 ESCC patients who underwent definitive chemoradiotherapy from January 2011 to December 2015. Patients were divided into the ENI group and the IFI group based on irradiation field extent. Propensity Score Matching with a 1:1 ratio was applied to balance confounding factors between the two groups. The changes in EDRIC and peripheral blood lymphocyte counts were compared. Spearman's rank correlation was utilized to evaluate the relationships between variables, and survival outcomes were analyzed.

Results: (1) A total of 212 patients (Stage II-III: 107; Stage IV: 105) with good balance in observed co-variables were enrolled. The 3-, 5-, and 10-year OS rates for patients receiving IFI were 30.1%, 22.0% and 16.3%, respectively, and for those receiving ENI, the rates were 27.7%, 15.9%, and 9.5%, respectively (p=0.458).(2)The mean EDRIC of patients receiving IFI was 6.83±2.06 Gy, whereas that of ENI was 8.77±2.16 Gy (p<0.001). EDRIC showed a positive correlation with PTV and a negative correlation with the lymphocyte nadir (r=0.527, p<0.001; r=-0.355, p<0.001). Patients receiving ENI experienced more G4 lymphopenia than those receiving IFI (21.70% versus 11.32%, p=0.042).(3)The OS, PFS and LRFFS rates of patient with EDRIC=7.82 Gy were significantly higher than those with EDRIC>7.82 Gy (p=0.014, 0.044, 0.020), with the 10-year OS and PFS rates at 19.2% versus 10.1% and 23.7% versus 15.0%, respectively. Multivariate analysis showed that high EDRIC was a significant independent predictor of poor prognosis.(4)Based on the median EDRIC (7.82 Gy) and the extent of the irradiation field (IFI vs. ENI), patients were divided into four groups. Pairwise comparisons indicated that patients receiving IFI with EDRIC =7.82 Gy experienced the best PFS and LRFFS among the four groups, with 5-, 10-year PFS rates of 34.4% and 29.6%, and 5-, 10-year LRFFS rates of 38.9% and 33.5%, respectively. The OS rates of patients receiving IFI with EDRIC=7.82 Gy were significantly higher than those receiving ENI with EDRIC>7.82 Gy. The 10-year OS rates were 26.2% versus 10.3%, respectively (p=0.010).

Conclusion: For esophageal carcinoma, both ENI and IFI treatments resulted in comparable long-term survival rates. However, ENI resulted in a higher EDRIC and a greater reduction in peripheral blood lymphocyte counts. A high EDRIC was an independent prognostic risk factor for survival. Esophageal cancer patients who received IFI and had an EDRIC =7.82Gy exhibited the best survival outcomes.