What provides an approximate skin dose where the x-ray beam is entering the patient?

What provides an approximate skin dose where the x-ray beam is entering the patient?

• A. Sievert
• B. Becquerel
• C. Air kerma
• D. Effective dose

Answer: (C)

Air kerma is the quantity that provides an approximate skin dose at the point the beam enters the patient. It measures the kinetic energy transferred from the x-ray photons to charged particles per unit mass of air in the beam’s path. Because the energy delivered to the skin is closely related to the energy that would be deposited in tissue along the entrance path, incident air kerma at the patient surface is used as a practical estimate of entrance skin dose (often adjusted with a backscatter factor to account for photons scattered back into the skin). The other options are not used for this purpose: sievert and effective dose are risk-based dose quantities for whole-body or organ-level effects, and becquerel is a measure of radioactivity, not dose.

Air kerma is the quantity that provides an approximate skin dose at the point the beam enters the patient. It measures the kinetic energy transferred from the x-ray photons to charged particles per unit mass of air in the beam’s path. Because the energy delivered to the skin is closely related to the energy that would be deposited in tissue along the entrance path, incident air kerma at the patient surface is used as a practical estimate of entrance skin dose (often adjusted with a backscatter factor to account for photons scattered back into the skin). The other options are not used for this purpose: sievert and effective dose are risk-based dose quantities for whole-body or organ-level effects, and becquerel is a measure of radioactivity, not dose.