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Centigray [cGy]: A Practical Unit in Radiation Therapy

The centigray (cGy) is a unit of absorbed radiation dose equal to 0.01 grays (Gy), or one-hundredth of a gray. It is widely used in clinical settings, especially in radiation therapy, where doses need to be both precise and clinically meaningful. One centigray equals 10 milligrays (mGy), making it a convenient unit for prescribing and documenting treatment doses.

In cancer treatment, therapeutic radiation is typically delivered in fractions, with each session often delivering 180–200 cGy (or 1.8–2.0 Gy) to the target area. Using centigrays allows healthcare professionals to express these fractions in whole numbers, simplifying treatment planning and communication. For example, a full course of radiation therapy might involve a total dose of 6000 cGy over several weeks.

Outside of therapy, the cGy is less commonly used, but it remains important in any context where mid-level radiation doses are applied or studied. Its use bridges the gap between small exposures (measured in mGy or µGy) and large, high-dose applications (measured in Gy), making the centigray a key unit in applied radiation science.

Picogray (pGy)

A picogray (pGy) is a very small unit of measurement used in the field of radiation physics and dosimetry. It belongs to the International System of Units (SI) and is a submultiple of the gray (Gy), which is the standard unit for absorbed radiation dose. One gray represents the absorption of one joule of radiation energy per kilogram of matter. Since a picogray is one trillionth of a gray (10⁻¹² Gy), it is an extremely tiny measure, often used in contexts where radiation levels are very low, such as environmental background radiation or highly sensitive biological experiments. Scientists and health physicists use pGy to quantify extremely small exposures that would otherwise be impractical to express in whole grays or even milligrays. For example, natural background radiation received by living organisms may sometimes be expressed in picograys when considering minute variations across different environments. This unit is important because even very small amounts of radiation can be significant in specialized studies, especially in medicine, space research, and nuclear safety. The adoption of the picogray allows researchers to describe radiation doses with greater precision and ensures consistency in international scientific communication.