**Question:** Linear accelerator produces

A. Electrons
B. Protons
C. Neutrons
D. Gamma rays

**Core Concept:** Linear accelerators (LINACs) are devices used in radiation oncology to generate ionizing radiation for cancer treatment. They primarily produce two types of particles: electrons and protons. Gamma rays are produced by other radiation sources, such as cobalt-60 devices, while neutrons are not a direct output of a linear accelerator.

**Why the Correct Answer is Right:** A linear accelerator is an electromagnetic device that accelerates charged particles, in this case, electrons and protons, to high speeds. When these particles collide with a target, they emit radiation, such as photons (gamma rays) and secondary particles (e.g., neutrons). In the context of this question, the correct answer focuses on the primary output of the linear accelerator: electrons and protons.

**Why Each Wrong Option is Incorrect:**

A. Electrons are the primary output of a linear accelerator, but the question overlooks the fact that protons are also a significant output.
B. Although protons are also generated by a linear accelerator, the focus of this question is on the primary outputs, which are electrons and protons.
C. Neutrons are not produced directly by a linear accelerator but are generated through a process called neutron activation, which occurs during post-acceleration processes in radiotherapy.
D. Gamma rays are a byproduct of neutron activation, not the primary outputs of a linear accelerator.

**Clinical Pearl:** Linear accelerators are versatile devices used in radiation therapy for cancer treatment. By adjusting the accelerator settings, physicians can tailor the energy, dose rate, and particle types (electrons, protons, or a combination of both) to target specific tumors effectively.