How does documenting the use of collimation during a radiographic exam impact dose calculation?

• A. It does not affect dose calculations.
• B. It increases the exposed area.
• C. Collimation reduces the area exposed, directly affecting the calculated dose.
• D. It only affects image sharpness.

Answer: (C)

Documenting collimation matters because the dose a patient receives depends on the tissue actually irradiated. Narrowing the X-ray beam to the region of interest reduces the field size, so for the same technique settings (mA, kVp, exposure time) the total energy imparted to the patient is smaller. When you record the collimated field, the dose calculation can be adjusted to reflect the true exposed area, often using dose-area concepts like the dose-area product. Without noting collimation, dose estimates can overstate patient exposure by assuming a larger field than was used. While collimation also helps reduce scatter and can improve image quality, the direct impact on dose calculation comes from the reduced area that is irradiated.