1573P Involved field and elective nodal irradiation presented similar treatment efficiency in concurrent chemoradiation for locally advanced ESCC

Concurrent chemoradiation is standard treatment for locally advanced esophageal squamous cell carcinoma (ESCC), while the optimal regimen of radiotherapy, especially in terms of total dose and planned range of target field, remained unclear. We performed this phase III clinical trial (ChiCTR-IPR-15007172) to compare the survival benefits between different radiation dose and different target field. This trial compared two radiation treatment aspects of total dose and field under two-by-two factorial design. The involved field irradiation (IFI) group and elective nodal irradiation (ENI) group adopted different radiation plans of clinical target volume. The high radiation dose group (HD) totally received 59.4Gy radiation and standard dose group (SD) received 50.4 Gy. The participants were assigned to one of the four groups (HD+ENI, HD+IFI, SD+ENI and SD+IFI) by simple randomization (1:1:1:1 ratio). The planned sample size was 147 in each arm (588 totally) and the primary endpoint was overall survival (OS). All statistical analysis was performed according to intention-to-treat principle. The median follow-up time reached 64.6 months up to April 2023. In comparison of target field, patients in IFI or ENI presented similar OS (HR=0.99, log rank test p =0.93) and PFS (HR=1.02). The HD treatment did not present significantly prolonged OS (HR=0.90, log rank test p value=0.318) compared with SD but suggested improved PFS (25.2 months to 18.0 months, HR=0.76). No significant synergistic effect was detected between dose and radiation field in interaction analysis (p=0.11). In subgroup analysis, the HD radiation suggested benefits in T4 tumors, and the ENI treatment was associated with better OS in N0 patients. No significant difference in occurrences of severe adverse events was detected in dose or field comparisons. The IFI has similar treatment efficiency to ENI, which indicated a reasonable choice for locally advanced ESCC. HD radiation did not suggest significant benefits in OS, but associated with better PFS compared to SD.