Radiation therapist degree and education. To become a radiation therapist, one should complete an entry-level education (high school diploma or GED or its equivalent) and complete a degree in radiation therapy.One can complete either a four-year bachelor’s degree in radiography or a two-year associate’s degree in radiation therapy from an accredited school.o become a radiation therapist, one should complete an entry-level education (high school diploma or GED or its equivalent) and complete a degree in radiation therapy.