Secondary shielding is designed to stop what?

• A. Neutrons only
• B. Primary beam
• C. Scatter and leakage
• D. Visible light

Answer: (C)

Secondary shielding is designed to reduce radiation that emerges from the treatment area after the beam interacts with material, mainly the scatter produced in the patient and surrounding components, plus any leakage from the machine housing. Scatter photons deflect in many directions, so even outside the direct beam path they can contribute dose to staff or adjacent areas. Leakage is the small amount of radiation that escapes the housing despite shielding and collimation. Both of these are what secondary shielding targets to keep exposure low in areas not in the direct beam line.

This isn’t about stopping the primary beam—that job belongs to primary shielding placed directly in the beam’s path. Visible light isn’t a radiation protection concern in this context, and while neutron shielding can be relevant at very high energies, the primary function of secondary shielding is to attenuate scatter and leakage photons, which are the main sources of stray dose in typical radiotherapy rooms.