The dose to the patient is directly related to which factor?

• A. Time
• B. Distance
• C. kVp
• D. mA

Answer: (A)

Dose to the patient changes most directly with how long the x-ray tube is energized. The longer the exposure lasts, the more photons are produced, and the more energy is deposited in the patient. This relationship is linear: doubling the exposure time doubles the dose, assuming all other factors stay the same. In radiography, the product mA × time (mAs) represents the total photon output, so time is the factor that most simply drives dose when you hold other variables constant.

Distance follows the inverse-square principle, so increasing distance reduces dose rather than increases it. kVp changes beam energy and penetrability and affects dose in a more complex way, not a direct one-to-one relation. Although increasing mA also increases dose, the question highlights the duration of exposure as the primary direct driver of dose in a single-variable context.