Figure 1. Visual computing for cohort-based radiation therapy (RT) prediction. A stylized 3D view of the predicted radiation plan of the current patient is placed centrally; top pale markers (front and back of eyes) receive the least radiation; tumors (black markers) receive the most. Additional RT views show the most similar patients under our novel T-SSIM measure, who contribute to the prediction; the most similar patient is currently highlighted (white) for comparison. A scatterplot (left) shows 4 clusters generated through the T-SSIM measure, with the current (cross) and comparison patient highlighted. A parallel-marker encoding (bottom) shows the predicted (blue cross) per-organ dose distribution within the context of the most similar patients; spatially collocated organs are in contiguous sections of the x-axis.Abstract-We describe a visual computing approach to radiation therapy (RT) planning, based on spatial similarity within a patient cohort. In radiotherapy for head and neck cancer treatment, dosage to organs at risk surrounding a tumor is a large cause of treatment toxicity. Along with the availability of patient repositories, this situation has lead to clinician interest in understanding and predicting RT outcomes based on previously treated similar patients. To enable this type of analysis, we introduce a novel topology-based spatial similarity measure, T-SSIM, and a predictive algorithm based on this similarity measure. We couple the algorithm with a visual steering interface that intertwines visual encodings for the spatial data and statistical results, including a novel parallel-marker encoding that is spatially aware. We report quantitative results on a cohort of 165 patients, as well as a qualitative evaluation with domain experts in radiation oncology, data management, biostatistics, and medical imaging, who are collaborating remotely.