Which of the following is a type of radiation therapy?

External radiation therapy is indeed a recognized type of radiation therapy used in oncology. This method involves the use of high-energy beams, typically X-rays, that are directed at a tumor from outside the body. The primary goal of external beam radiation is to damage the DNA of cancer cells, causing them to die or be unable to multiply. It can be precisely targeted to minimize damage to surrounding healthy tissues, making it a common choice for treating various types of cancer.

In contrast, surgical radiation refers to intraoperative radiation therapy and is more specific and less utilized. Thermal radiation is not a standard term within the context of cancer treatment and typically does not refer to any established therapeutic method for oncology. Chemotherapeutic radiation is misleading as chemotherapy and radiation are two distinct treatment modalities, with chemotherapy involving the use of drugs to kill cancer cells through systemic effects. Thus, external radiation therapy stands out as a widely accepted and specifically defined treatment in the field of oncology.