Increasing the kVp from 60 to 69 kVp with identical technique parameters yields receptor exposure of which value?

Increasing the kVp from 60 to 69 kVp with identical technique parameters yields receptor exposure of which value?

• A. 10 Gy
• B. 17.5 Gy
• C. 20 Gy
• D. 25 Gy

Answer: (C)

When you raise the kilovoltage while keeping all other exposure factors the same, the beam becomes more penetrating and delivers more photons to the image receptor. A common approximation for how receptor exposure changes with kVp at fixed mA and time is that it varies with the square of kVp: I ∝ (kVp)^2. So the new exposure is the old exposure multiplied by (69/60)^2. That factor is about (1.15)^2 ≈ 1.32, a roughly 32% increase. If the exposure at 60 kVp was 15 Gy, it becomes 15 × 1.32 ≈ 19.8 Gy, which rounds to about 20 Gy. Therefore the receptor exposure is about 20 Gy. The other values would require a smaller or larger change than this 32% increase.

When you raise the kilovoltage while keeping all other exposure factors the same, the beam becomes more penetrating and delivers more photons to the image receptor. A common approximation for how receptor exposure changes with kVp at fixed mA and time is that it varies with the square of kVp: I ∝ (kVp)^2.

So the new exposure is the old exposure multiplied by (69/60)^2. That factor is about (1.15)^2 ≈ 1.32, a roughly 32% increase. If the exposure at 60 kVp was 15 Gy, it becomes 15 × 1.32 ≈ 19.8 Gy, which rounds to about 20 Gy.

Therefore the receptor exposure is about 20 Gy. The other values would require a smaller or larger change than this 32% increase.