1. A method for real-time position estimation of an oncology target in a patient, comprising: continuous monitoring of a respiratory signal of the patient; imaging of the target using a single imaging device, the imaging being done periodically to limit radiation dosage administered by the single imaging device; applying a model to estimate a centroid position of the target from a combination of said respiratory signal and target position data from said imaging; determining and updating parameters of said model by using position displacement data from said imaging; and applying said updated model in real-time to a treatment program.