Final answer:
The correct answer to the branch of healthcare that deals with treating cancer using radiation is Radiation Oncology (D). This field employs high-energy radiation to target and destroy cancer cells, which can be delivered externally or internally.
Step-by-step explanation:
The branch of healthcare involved in the treatment of disease, particularly cancer, by means of high-energy radiation and/or radioactive substances is D) Radiation Oncology. Radiation therapy, a component of radiation oncology, utilizes high-energy radiation to damage the DNA of cancer cells, leading to their death or preventing them from dividing. Oncologists employ this therapy in various forms, including external beam radiation therapy from outside the body or internal radiation therapy (brachytherapy) using a radioactive substance introduced into the body. This therapy may be administered alone or in conjunction with other treatments such as surgery and chemotherapy, and is a critical tool in cancer management.