The impact of adjuvant radiotherapy (aRT) on overall survival (OS) in early-stage type II endometrial carcinoma (EC) remains uncertain. This study aimed to develop nomograms and a web-based calculator to identify these patients who may benefit from aRT.

Data were extracted from the Surveillance, Epidemiology, and End Results (SEER) database and divided into the developing and validation cohorts. LASSO Cox regression identified prognostic factors, and nomograms were constructed to predict 1-, 3-, and 5-year OS with/without aRT. The expected OS benefit from aRT was reflected in the difference between the two predicted OS nomograms. Validation involved ROC analysis, calibration curves, and decision curve analysis. A web calculator was created for estimating aRT's net OS benefit.

Among the 6084 patients, aRT did not improve OS across all patients but showed benefits in specific subgroups, such as those with clear cell carcinoma and carcinosarcoma. Nomograms were constructed for patients with/without aRT to predict 1-, 3-, and 5-year OS, and they can accurately forecast OS. Additionally, the web-based calculator was developed to estimate the net OS benefit of aRT.

The nomograms provide accurate OS estimates for early-stage type II EC patients with/without aRT, thereby supporting individualized treatment decisions. The web calculator offers a quantitative tool for optimizing aRT use based on clinicopathological characteristics.