Computed tomography (CT) is frequently used for medical scanning and can deliver high doses of radiation to patients. Yet because few standards exist for CT examinations, the radiation doses that patients receive during CT vary widely. Routinely, doses are higher than needed for medical diagnoses-and high enough to be associated with increased cancer risk. The proposed project is a multisite collaboration studying improved standards for conducting CT, including the radiation doses used, and developing strategies to apply (implement) and spread (disseminate) these standards in different clinics and hospitals. The project will use a mixture of methods including a randomized controlled trial, observational data, and key informant interviews. The work strives to improve CT safety and cancers associated with radiation from CT by lowering the doses that patients receive. The project includes an implementation trial to learn how to broadly teach clinics and hospitals about the best and safest CT practices. The process of change will vary with different health care settings and different organizational structures. This study seeks to understand the best strategies to adapt CT safety interventions by learning what factors improve both implementation and dissemination of the best practice guidelines. Our project is a partnership with diverse health care delivery organizations in the US, Canada, and Europe in collaboration with Bayer Health. These public, private, academic, and community-based care systems include both fee-for-service and prepaid care organizations and will serve as our test bed sites. Non-US institutions are included since radiation safety around medical imaging is a great concern in these countries, and their hospitals and researchers have experience in CT radiation dose monitoring and optimizing. Our research team includes scientists with expertise in biostatistics, radiology, radiation physics, and dissemination and implementation sciences, and health system leaders who focus on quality improvement and are champions for optimizing medical imaging doses. All participating health care systems already use eXposure, the Bayer Health software for radiation dose monitoring. The purchase of eXposure shows the interest and commitment of the health care organizations to collecting data on the radiation doses used in clinical practice and using data to optimize medical imaging doses. The sites are thus ideal partners for this project. Each has project champions, but not the expertise or strategy to optimize CT radiation dosages. Organizing the project around existing relationships that can already collect data securely from a range of software platforms minimizes data collection complexity, overcoming a main hurdle in developing a widely implementable quality improvement program. This will allow our research team to focus on the proposed study aims of disseminating and implementing change. We will 1) conduct a randomized controlled pragmatic trial with a stepped-wedge design to compare simple audit with feedback vs. a tailored, multicomponent intervention as strategies for facility-level optimization of CT radiation dose, 2) assess the degree of implementation and identify facilitators, barriers and successful and failed strategies for implementing dose optimization and sustaining improvements in CT radiation dosing over 2 years following intervention, and 3) broadly disseminate and evaluate dissemination of the intervention at several institutions, focusing on the most effective solutions from the pragmatic trial.