Any radiation treatment has the potential to damage DNA in healthy cells. Which lists therapeutic uses of radiation based on the likelihood of affecting healthy cells in order from least likely to most likely?

Brachytherapy places the radiation source in or very near the tumor, so nearby healthy tissue is exposed less than with the other methods. Radiopharmaceuticals travel through the body, which can expose healthy tissues that take them up. Deep external beam radiation passes through healthy tissue on its way to a tumor deep inside the body, making it most likely to affect healthy cells. Thus the order is brachytherapy, radiopharmaceuticals, then deep external beam radiation therapy.

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