1. A radiation treatment planning apparatus comprising: a processor configured to: generate a statistical model for a change in radiation therapy plan (RTP) data based on change data of RTP data collected in association with radiation therapy results data; set first RTP data based on a medical image of a region of interest of a patient; acquire radiation therapy results data based on the first RTP data; acquire statistical data corresponding to the first RTP data and the radiation therapy results data from the statistical model; and generate second RTP data using the statistical data.