Absorbed dose (D) is commonly used to describe which of the following?

• A. quantity of radiation directed at the patient
• B. quantity of radiation passing through the patient
• C. quantity of radiation absorbed in the patient
• D. quantity of radiation scattered from the patient

Answer: (C)

Absorbed dose describes how much energy from the ionizing radiation actually gets deposited in tissue per unit mass. In diagnostic radiology, as the x-ray beam travels through the body, some energy is absorbed by tissues, some is scattered, and some passes through. The absorbed dose, D, is defined as the energy imparted to a mass of tissue per kilogram (dE/dm), measured in grays (1 Gy = 1 J/kg). This makes it the best descriptor for the amount of radiation energy that remains in the tissue and can cause biological effects. The other options describe the beam before or after interaction—energy directed at the patient (incident beam), energy that passes through (transmitted), or energy scattered away—not the energy actually deposited in the tissue.