Where is brachytherapy administered?

Brachytherapy is a form of radiation therapy where a radioactive source is placed inside or very close to the tumor. It is commonly administered through various routes, including intravaginally, intravesically, or directly into a tumor, which is why the option indicating intracavitary administration is correct.

Intracavitary brachytherapy involves placing the radioactive source within a body cavity, effectively targeting the tumor while minimizing exposure to surrounding healthy tissues. This method is particularly useful for cancers in locations such as the cervix, uterus, and other areas where direct access to the tumor is possible.

The other options represent different methods of administering treatments or therapies but do not pertain to brachytherapy specifically. For example, oral administration typically relates to medications taken by mouth, while external radiation therapy involves directing beams of radiation from outside the body onto the tumor. Intraperitoneally would refer to treatment delivered within the abdominal cavity, which is not a standard route for brachytherapy.