You can take online college courses to become a radiation therapist and you can do most of your studies online through a college course.
However even though you can do the majority of your studying online to become a radiation therapist you still need to go to a college to get hands on experience.
Then after you do your online college courses for radiation therapist and pass those exams you will need to also go to college and get hands on experience or work alongside a doctor and learn how to hands on how to become the radiation therapist.
You'll be supervised while working as an intern as a radiation therapist in some places.
Most college courses for most careers can be done online through online college courses without needing to step foot into a college for at least most of the studying.