Final answer:
A patient undergoing internal radiation therapy, or brachytherapy, which involves the introduction of radioactive substances into the body, is considered radioactive. In contrast, external radiation therapy does not render the patient radioactive since it's delivered from outside the body. The radioactive substances used in brachytherapy can include iodine-131 or actinium-225, among others.
Step-by-step explanation:
When comparing which patient is considered radioactive between one undergoing internal radiation therapy and one undergoing external radiation therapy, the patient with internal radiation therapy would be considered radioactive. Internal radiation therapy, or brachytherapy, involves the introduction of a radioactive substance into the body. Examples of this include the use of iodine-131 for treating hyperthyroidism or actinium-225 attached to a monoclonal antibody for prostate cancer treatment. These radioactive substances can emit radiation from within the body, making the patient radioactive. On the other hand, external radiation therapy involves a machine that delivers radiation to the patient from outside the body, so the patient does not become radioactive. Brachytherapy can involve the implantation of pellets or rods that emit radiation, and as long as these are inside the body, the patient will emit radiation and thus be considered radioactive.