Automated evaluation of organ sparing in prostate stereotactic body radiation therapy using dose-gradient metrics.

Background and purpose: Traditional dose-volume histogram (DVH) metrics used in radiotherapy plan evaluation lack spatial information and are sensitive to organ volume variations. This study investigated the use of Dose Gradient Curves (DGCs) as a robust, volume-independent alternative for assessing organ sparing in prostate stereotactic body radiation therapy (SBRT). Materials and methods: Treatment plans of 154 prostate cancer patients were retrospectively analysed. A benchmark set of 20 high-quality plans was established, and average DVH (aDVH) and DGC (aDGC) curves were derived for the bladder and anorectum. Plan quality of the remaining 134 plans was assessed using aDVH, aDGC, and expert-reviewed ground truth. A ΔAUC-based classifier was developed to automatically detect suboptimal organ sparing. The robustness of benchmark set size was evaluated by comparing subsets of five plans with extreme organ volumes. Results: The inclusion of dose-gradient information improved accuracy and precision compared to DVH-based methods. For the bladder, DGC analysis achieved 99% accuracy and precision, compared to 87% and 94% for DVH. For the anorectum, DGC yielded 97% accuracy and 100% precision. The ΔAUC classifier achieved F1 scores of 97.1% (bladder) and 89.7% (anorectum). Reducing the benchmark set to five plans did not significantly affect DGC-based evaluations, unlike DVH-based assessments. Conclusions: DGC-based plan evaluation offers a reliable and volume-independent method for assessing organ sparing in prostate SBRT. It enabled automated detection of suboptimal plans and remained robust even with reduced benchmark sizes. Further investigation prior to clinical implementation is required.