Image Storage Requirements for Treatment Planning and Verification

Digital imaging techniques are becoming increasingly accepted in radiation therapy, and they bring significant advantages when compared with film, especially the ease of storage and retrieval. A simple model is proposed for the estimation of digital data storage requirements in a typical department of radiation therapy. The model assumes that 100 patients are undergoing treatment at any given time, and their computed tomography (CT) images, treatment plans, digitized simulator films, and portal images are to be available at short notice ("on-line"). Off-line archival image storage is required after the completion of treatment, for 1,000 patients per year. Reasonable assumptions are postulated regarding image sizes and acquisition rates, and on-line storage requirements are estimated to be up to 300 megabytes (MB) for CT data, 170 MB for treatment plans, 200 MB for digitized simulator films, and 500 MB for digitized port films. If electronic portal imaging is used instead of port films, the on-line requirement becomes about 2 gigabytes (GB) for verification images, and 20 GB if portal movies are to be archived. Off-line storage requirements are a factor of ten larger. It is suggested that data compression may reduce these requirements by up to a factor of 20.