Mid-trial dosimetric analysis of the korean radiation oncology group 19 − 09 multi-institutional prospective cohort study on breast cancer

Background The Korean Radiation Oncology Group 19 − 09 multi-institutional clinical trial investigates the effect of regional nodal irradiation (RNI) omission on regional recurrence rates after neoadjuvant chemotherapy followed by breast-conserving surgery, and sentinel lymph node biopsy in cT1-3N1 and ypN0 breast cancer patients. This mid-trial analysis evaluates dosimetric deviations among enrolled patients using an artificial intelligence (AI) auto-contouring engine. Methods We analyzed dose-volume histograms of 366 patients enrolled from eight institutions based on an AI auto-contoured reference structure set. Of these, 176 received whole breast and regional nodal irradiation (WBI + RNI), while 190 received whole breast irradiation only (WBI). Results Dosimetric outliers were observed in both groups. In the WBI + RNI group, 25 (14%) and 30 (17%) patients were outliers in D95% of axillary levels II and III, respectively. The corresponding counts in the WBI group were 17 (9%) and 16 (8%), respectively. Especially, 7 (58%) of 12 patients treated by one physician in the WBI + RNI group were outliers for axillary level III. Similarly, among the 49 patients treated by another physician in the WBI + RNI group, 21 (43%) were outliers for axillary level II and 21 (43%) for level III. Regarding the breast CTV, all outlier patients except one were treated by the two physicians. Conclusion Significant dose deviations were observed, indicating that comparing the WBI + RNI and WBI groups alone may inadequately assess the clinical impact of RNI omission. Therefore, the final analysis will evaluate the association between specific regional nodal doses and clinical outcomes.