What is the effect of decreasing the target-to-skin distance from 40 inches to 38 inches?

Decreasing the target-to-skin distance (TSD) from 40 inches to 38 inches results in an increase in patient dose. This is primarily due to the inverse-square law, which states that the intensity of radiation is inversely proportional to the square of the distance from the source. When the distance is reduced, the exposure to radiation increases significantly.

In this specific scenario, moving from 40 inches to 38 inches represents a small change in distance, but because of the geometric relationship dictated by the inverse-square law, even a slight decrease in distance can lead to a higher radiation dose. The calculations suggest that this distance reduction can yield about an 11% increase in patient dose, as the radiation intensity more than compensates for the short distance change.

Thus, the correct answer captures the significant impact of distance on radiation exposure and reinforces the principle that closer proximity to the radiation source results in higher doses delivered to the patient.