Which term describes radiotherapy delivered from outside the body?

• A. Brachytherapy
• B. Stereotactic radiosurgery
• C. Proton therapy
• D. External beam irradiation

Answer: (D)

When radiation therapy is delivered from outside the body, the treatment beams come from machines located outside the patient and pass through the skin to reach the tumor. This approach is called external beam irradiation. It contrasts with brachytherapy, where the radiation source is placed inside or very near the tumor, delivering dose from within. Proton therapy is a specific external beam modality that uses protons instead of photons, as another way to deliver the same outside-the-body approach. Stereotactic radiosurgery is a highly precise form of external beam radiotherapy, but the general term for radiotherapy given from outside the body is external beam irradiation.