What is the SI unit used for measuring absorbed dose in patients?

The correct answer is the Gray (Gy), specifically referring to the absorbed dose of radiation. The Gray is defined as the absorption of one joule of radiation energy by one kilogram of matter—in this case, human tissue. This unit is critical in the field of radiology and radiation therapy, as it provides a measurable way to assess the amount of radiation energy that is absorbed by biological tissues, which is essential for evaluating the potential biological effects of exposure to radiation.

While the Sievert (Sv) also relates to radiation exposure, it is primarily used to quantify the biological effects of radiation, taking into account the type of radiation and its impact on different tissues. Röntgen (R) is an older unit related to the measurement of ionization in air, not directly applicable for absorbed dose in tissues. The Rem is a traditional unit considering biological effects but has largely been replaced by the Sievert due to its more comprehensive nature. Thus, the Gray is the most relevant choice when specifically discussing the measurement of absorbed dose in patients.