Knowledge-based radiotherapy treatment planning is expanded to include spatial information from, for example, positron emission tomography (PET). Information that is specific to a patient is accessed. A prediction of a spatial dose distribution inside a target volume in the patient is determined using the patient-specific information as an input to a prediction model. The prediction model is established using training data that includes data resulting from applying other radiation treatment plans to other patients. The training data includes spatially distributed information indicating a level of activity in target volumes in the other patients (e.g., PET image data). A dose-volume histogram and associated three-dimensional dose distribution information based on the prediction are produced. The dose-volume histogram and the three-dimensional dose distribution information can be used to develop a radiation treatment plan for the patient.
