The purpose of this retrospective study is to evaluate the cumulative imaging doses, the associated cancer risk and the cost related to the various radiological imaging procedures in image-guided radiotherapy of cancers. Correlations between patients' size and Monte Carlo simulated organ doses were established and validated for various imaging procedures, and then used for patient-specific organ dose estimation of 4,832 cancer patients. The associated cancer risk was estimated with published models and the cost was calculated based on the standard billing codes. The average (range) cumulative imaging doses to the brain, lungs and red bone marrow were 38.0 (0.5-177.3), 18.8 (0.4-246.5), and 49.1 (0.4-274.4) cGy, respectively. The associated average (range) lifetime attributable risk of cancer incidence per 100,000 persons was 78 (0-2798), 271 (1-8948), and 510 (0-4487) for brain cancer, lung cancer and leukemia, respectively. The median (range) imaging cost was $5256 (4268-15896) for the head scans, $5180 (4268-16274) for the thorax scans, and $7080 (4268-15288) for the pelvic scans, respectively. The image-guidance procedures and the accumulated imaging doses should be incorporated into clinical decision-making to personalize radiotherapy for individual patients.