1The app is well structured and easy to use. 2The app content is relevant to radiation oncology. 3The audio lessons enhanced my learning. 4The quizzes and cases enhanced my learning. 5My overall knowledge in radiation oncology has increased. 6I would recommend this application to a colleague. 25 participants completed the survey on the advanced learning module. 70% of all survey participants ""agree"" or ""strongly agree"" to the five statements listed below: 1The module was well structured. 2The module is relevant to radiation oncology. 3The module was an appropriate level of complexity. 4My overall knowledge about breast cancers has increased. 5I would recommend this module to a colleague. Overall, the application and advanced learning modules were well received and the trainees express a desire for other advanced learning modules in the free text responses. This free smartphone application provides an easily accessible resource for self-directed learning in radiation oncology. Initial feedback was very favourable and recommended use of this innovative learning resource among a wider group of trainees. In response to trainee feedback, future work will focus on the development of additional modules, incorporating interactive virtual patient cases, in other tumour sites. As web-based learning continues to become increasingly popular, this application can be a useful educational resource for medical trainees." Background Radiation oncology (RO) textbooks and primary references are often complex, technically advanced, and inaccessible to medical trainees. To address this, we designed a free, interactive smartphone application, to introduce trainees to the basics of RO. Methods We created and implemented an Apple iOS smartphone application with RO content, targeted for medical trainees. The beta version is free for download via the TestFlight application (https://testflight.apple.com/join/4A6qXjq2). The application incorporates both introductory topics relevant to radiation oncology and advanced, site-specific modules, that focus on the different tumour sites and their management. Content includes written text, audio lectures, interactive quizzes, and clinical cases. Two questionnaires were implemented to elicit feedback; one for application design and the other a knowledge-quiz for an advanced learning module on breast cancers. Both contain quantitative 5-point Likert-scale questions and one qualitative freeform text question seeking suggestions for improvement. Results There have been over 70 unique downloads of the application. 40 participants completed the survey on application design. Over 80% have selected ""agree"" or ""strongly agree"" to the six statements listed below: Radiation oncology (RO) textbooks and primary references are often complex, technically advanced, and inaccessible to medical trainees. To address this, we designed a free, interactive smartphone application, to introduce trainees to the basics of RO. We created and implemented an Apple iOS smartphone application with RO content, targeted for medical trainees. The beta version is free for download via the TestFlight application (https://testflight.apple.com/join/4A6qXjq2). The application incorporates both introductory topics relevant to radiation oncology and advanced, site-specific modules, that focus on the different tumour sites and their management. Content includes written text, audio lectures, interactive quizzes, and clinical cases. Two questionnaires were implemented to elicit feedback; one for application design and the other a knowledge-quiz for an advanced learning module on breast cancers. Both contain quantitative 5-point Likert-scale questions and one qualitative freeform text question seeking suggestions for improvement. There have been over 70 unique downloads of the application. 40 participants completed the survey on application design. Over 80% have selected ""agree"" or ""strongly agree"" to the six statements listed below: