[en] Not many people know of a field called “medical physics” and that there are physicists working in hospitals. The roles of physicists in medicine include: 1) developing x-ray images for disease diagnosis; 2) ensuring radiation safety for patients and hospital workers; 3) ensuring accurate and precise radiation therapy delivery. X-rays have been used in medicine since their discovery more than a hundred years ago. In imaging, medical physicists use x-rays to construct three dimensional anatomic images, assisting physicians to see the internal anatomy of a patient without cutting the patient open. In therapy, medical physicists ensure the powerful x-ray aim toward to cancer site, killing the cancer cells. With these medical applications, medical physicists apply their knowledge in nuclear physics and modern physics to play the essential roles. In this presentation, we will show some examples of specific physicist’s roles in medicine. (author)