centigray

The centigray (cGy) is an SI-derived unit used to express absorbed dose of ionizing radiation. It quantifies the amount of energy deposited by radiation per unit mass of matter, with one centigray equaling 0.01 gray. Because the gray is defined as one joule of energy absorbed per kilogram, a centigray corresponds to 0.01 joules per kilogram absorbed by tissue.

In relation to older units, 1 cGy equals 1 rad, and conversely 1 Gy equals 100 cGy and 100 rad. The centigray is thus a convenient subunit when expressing doses on a scale closer to whole gray values, such as 60 cGy or 2 Gy, which are common in clinical practice.

The centigray measures absorbed dose—energy deposition within tissue—independent of radiation type. It does not by itself convey biological effect; to assess risk or required protection standards, the absorbed dose is typically converted to equivalent or effective dose in sieverts, using radiation weighting factors and tissue-tolerance considerations.

Usage of the centigray has diminished in favor of the gray in many contexts, because the gray is the standard SI unit. However, cGy remains encountered in older literature and in some clinical settings, especially when doses are discussed in a scale familiar to radiotherapy. The unit is appropriate for comparing doses within a single tissue or procedure, provided the limitations related to biological effect are acknowledged.