Postoperative tumor bed radiation versus T-shaped field radiation in the treatment of locally advanced thoracic esophageal squamous cell carcinoma: a phase IIb multicenter randomized controlled trial.

Background: Postoperative radiotherapy (PORT) is crucial for patients with thoracic locally advanced esophageal squamous cell carcinoma (LA-ESCC, pT3-4aN0-3M0) following esophagectomy. However, the appropriate radiation volume has not been well established. This study aimed to determine the optimal PORT volume for LA-ESCC patients.

Methods: LA-ESCC patients post-esophagectomy were randomly assigned to either the large-field irradiation (LFI, primary lesion and lymph node tumor bed plus elective nodal irradiation) group or the small-field irradiation (SFI, primary lesion and lymph node tumor bed alone) group. Stratification was based on T stage and the number of lymph node metastases. The primary endpoint was disease-free survival (DFS), while the secondary endpoints included overall survival (OS), adverse events, and patterns of initial failure.

Results: A total of 401 patients were randomly assigned to the intention-to-treat analysis(LFI group, n = 210; SFI group, n = 191). The median DFS of patients in the LFI group was 47.9 months and 48.1 months in the SFI group (HR = 0.87, 95%CI, 0.65 to 1.16; p = 0.32). The estimated one-year and three-year OS rates were 89.2% and 63.2% for patients in the LFI group, compared to 86.6% and 60.7% for the SFI group, respectively. The difference of OS between the two groups was not significant (HR = 0.86, 95%CI, 0.63 to 1.16; p = 0.35). Fewer patients in the LFI group experienced locoregional recurrence compared to the SFI group (12.9% vs 20.4%, p = 0.013). Additionally, locoregional recurrence-free survival of the LFI group was significantly longer than that of SFI group (HR = 0.54, 95%CI, 0.34-0.87; p = 0.01). The most common toxicity was grade 2 esophagitis, observed in 22.9% of the LFI group and 16.8% of the SFI group. Grade 3 adverse events occurred in 6.7% of the LFI group and 2.6% of the SFI group. No grade 4 or 5 toxicities were observed. Adverse events did not significantly differ between the two groups.

Conclusions: Postoperative radiotherapy, with the specified radiation volume shows encouraging survival outcomes that are comparable to those of neoadjuvant chemoradiotherapy in patients with thoracic LA-ESCC. Both postoperative irradiation fields were found to be feasible and safe.