Which of the following units measures radiation dose absorbed by the body?

The correct unit to measure the radiation dose absorbed by the body is the Gray (Gy). This unit quantifies the amount of radiation energy absorbed per kilogram of tissue, making it a direct measure of absorbed dose. The use of the Gray is vital in the context of radiation therapy as it provides a clear understanding of how much radiation a patient receives, which is crucial for treatment planning and ensuring safety.

While Sieverts and REMs also relate to radiation, they are specifically used to quantify biological effects of radiation exposure. The Sievert accounts for the biological impact of dose on human tissue, considering factors like the type of radiation. The REM, which stands for "roentgen equivalent man," is a now largely obsolete unit that also considers biological effects but has been largely replaced by the Sievert in most applications.

Roentgen is a unit primarily related to the exposure to X-rays and gamma rays and does not measure absorbed dose, but rather the ionization produced in air. Thus, understanding that the absorbed dose is specifically quantified by the Gray is key in radiation protection and therapy.