Abstract: Methods of predicting relapse of a prostate cancer patient treated by radiation therapy, associated software, and systems for implementing such methods. Patient-specific PSA data are collected including np measurements of serum prostate specific antigen (PSA) at np dates for a newly-diagnosed prostate cancer patient before and after an external beam radiation therapy (EBRT) regimen. Patient-specific parameters P0, ?n, ?s, ?d, and RD are identified that render an optimal fit of the patient-specific PSA data to a personalized model. Using the personalized model and the patient-specific parameters, a set of one or more predicted PSA values are calculated at one or more time horizons from 0 to 2 years after the last PSA measurement. If and/or when a relapse of the prostate cancer patient will occur is predicted based on the one or more predicted PSA values.