Which of the following is a form of external beam radiation therapy?

Both intensity-modulated radiation therapy (IMRT) and stereotactic radiation therapy are indeed forms of external beam radiation therapy.

Intensity-modulated radiation therapy is a sophisticated form of radiation that allows for the precise delivery of radiation doses to a tumor while minimizing exposure to surrounding healthy tissue. It achieves this through the modulation of the intensity of the radiation beams, meaning that different areas of the target can receive varying doses of radiation based on the tumor's shape and location.

Stereotactic radiation therapy, on the other hand, involves delivering highly focused radiation beams to tumors, often with a high degree of accuracy. It can be used for both treatment and diagnostic purposes and is particularly effective for treating small tumors or lesions, usually in the brain or other parts of the body, with minimal impact on the surrounding normal tissues.

Both IMRT and stereotactic techniques utilize external beams to irradiate the tumor from outside the body, confirming that they fall under the umbrella of external beam radiation therapy. Thus, the correct answer reflects the inclusion of both modalities as viable forms of this therapy.