An efficient method and system of contouring target volumes and normal tissues at risk using an expert case as interactive tutorial reference for radiation therapy treatment plan is disclosed. Target volume contours based on guidance from a disease-matched expert case is selected by the user. The second imaging data set of a new patient is then displayed and linked with expert's case in a the slice-by-slice and side-by-side fashion and at comparable field-of-view angles. Users can generate the target volume contours on the new patient using expert case as tutorial guidance or overlaying the expert contours onto the new patient's imaging data set followed by reforming the target volume contours to fit the anatomical terrain of the patient. Users can then modify the target volume contours of their patient using expert case as tutorial guidance linked in a the slice-by-slice and side-by-side fashion and at comparable field-of-view angles.