Which technology produces a photon beam by accelerating electrons with microwave energy fired from an electron gun?

• A. External Beam
• B. Linear Accelerators
• C. Brachytherapy
• D. Cobalt-60 Unit (Gamma Knife)

Answer: (B)

A linear accelerator uses microwave energy to accelerate electrons from an electron gun to high speeds, and then these fast electrons are directed at a high‑Z target to produce a photon beam. The photons are high-energy x-rays that form the external beam used to treat tumors. This setup is the standard way to generate external beam photon therapy, with beam energy and shaping options (like tailoring with collimators) to fit the tumor.

If you think about the other options, they don’t fit this mechanism: brachytherapy relies on radioactive sources placed inside or near the tumor, delivering radiation from within the body rather than as a beam produced by an accelerator. A cobalt‑60 unit emits gamma rays from a decaying radioactive source, not photons generated by accelerating electrons with microwaves. External Beam is the delivery method, but the specific technology that creates the photon beam in this context is the linear accelerator.