If a radiologic technologist reduces the mAs from 50 to 20 while increasing the kVp from 76 to 94, what would the new entrance skin dose (ESD) be if the old ESD was 6 mGya?

To understand why the new entrance skin dose (ESD) would be 3.6 mGya after reducing the mAs and increasing the kVp, it is crucial to grasp how mAs and kVp affect radiation dose.

The entrance skin dose is influenced by both milliampere-seconds (mAs) and kilovoltage peak (kVp). The mAs is directly proportional to the amount of radiation produced; thus, reducing the mAs directly decreases the radiation dose. Conversely, increasing the kVp enhances the quality and penetrability of the X-ray beam, leading to more efficient imaging, which can decrease the dose required to achieve a diagnostic image.

In this scenario, the mAs is reduced from 50 to 20, which results in a decrease (specifically to 40% of the original value since 20 is 40% of 50). In terms of dose, if we calculated the effect solely from the change in mAs, the entrance skin dose would decrease proportionally.

However, the increase in kVp from 76 to 94 increases the quality of the X-ray beam, effectively allowing for fewer photons to be required to produce a quality image. The increase in kVp affects the dose because