When the source-to-image distance (SID) is increased, the absorbed dose to the patient will

When the source-to-image distance (SID) is increased, the absorbed dose to the patient will

• A. Increase
• B. Decrease
• C. Remain the same
• D. Fluctuate

Answer: (B)

Increasing the source-to-image distance lowers the dose the patient receives because the X-ray beam spreads out as it travels, and intensity follows the inverse square law. That means if you double the distance, the beam reaching the patient is reduced to one-quarter of its previous value, so the absorbed dose decreases, provided the exposure factors (mA and exposure time) are not changed. In practice, if you need the same image receptor exposure after increasing distance, you’d raise the exposure factors, which could offset the dose reduction, but with no change to exposure factors, the patient dose goes down as distance goes up.

Increasing the source-to-image distance lowers the dose the patient receives because the X-ray beam spreads out as it travels, and intensity follows the inverse square law. That means if you double the distance, the beam reaching the patient is reduced to one-quarter of its previous value, so the absorbed dose decreases, provided the exposure factors (mA and exposure time) are not changed. In practice, if you need the same image receptor exposure after increasing distance, you’d raise the exposure factors, which could offset the dose reduction, but with no change to exposure factors, the patient dose goes down as distance goes up.