Prostate cancer is the second most common cancer in men, and almost 300,000 individuals are diagnosed with it each year in the U.S. To develop a consistent method of estimating prostate cancer size, which can help clinicians more accurately make informed treatment decisions, Mass General Brigham researchers trained and validated an AI model based on MRI scans from more than 700 prostate cancer patients. The model was able to identify and demarcate the edges of 85% of the most radiologically aggressive prostate lesions. Tumors with a larger volume, as estimated by the AI model, were associated with a higher risk of treatment failure and metastasis, independent of other factors that are normally used to estimate this risk. Furthermore, for patients who received radiation therapy, the tumor volume performed better than traditional risk stratification for predicting metastasis. Researchers believe the tool could be used to help clinicians understand a tumor’s aggressiveness, to inform more personalized treatment plans, and to guide radiation therapy. The study is published in the journal Radiology.