Harmonizing organ-at-risk structure names using open-source large language models

Background and purpose: Standardized radiotherapy structure nomenclature is crucial for automation, inter-institutional collaborations, and large-scale deep learning studies in radiation oncology. Despite the availability of nomenclature guidelines (AAPM-TG-263), their implementation is lacking and still faces challenges. This study evaluated open-source large language models (LLMs) for automated organ-at-risk (OAR) renaming on a multi-institutional and multilingual dataset. Materials and methods: Four open-source LLMs (Llama 3.3, Llama 3.3 R1, DeepSeek V3, DeepSeek R1) were evaluated using a dataset of 34,177 OAR structures from 1684 patients collected at three university medical centers with manual TG-263 ground-truth labels. LLM renaming was performed using a few-shot prompting technique, including detailed instructions and generic examples. Performance was assessed by calculating renaming accuracy on the entire dataset and a unique dataset (duplicates removed). In addition, we performed a failure analysis, prompt-based confidence correlation, and Monte Carlo sampling-based uncertainty estimation. Results: High renaming accuracy was achieved, with the reasoning-enhanced DeepSeek R1 model performing best (98.6 % unique accuracy, 99.9 % overall accuracy). Overall, reasoning models outperformed their non-reasoning counterparts. Monte Carlo sampling showed a stronger correlation with prediction errors (correlation coefficient of 0.70 for DeepSeek R1) and better error detection (Sensitivity 0.73, Specificity 1.0 for DeepSeek R1) compared to prompt-based confidence estimation (correlation coefficient < 0.42). Conclusions: Open-source LLMs, particularly those with reasoning capabilities, can accurately harmonize OAR nomenclature according to TG-263 across diverse multilingual and multi-institutional datasets. They can also facilitate TG-263 nomenclature adoption and the creation of large, standardized datasets for research and AI development.