American Registry of Radiologic Technologists (ARRT)
What you will find: provides certification in four disciplines, including radiation therapy.
Radiation Research Society
What you will find: hosts an annual conference, provides information on jobs, funding and fellowships, and publishes a newsletter.
Radiation Therapy Oncology Group (RTOG)
What you will find: conducts clinical trials on cancer treatments and provides publications that discuss results from research and clinical trials.