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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.

Femtogray [fGy]: A Tiny Unit of Radiation Dose

The femtogray (fGy) is a unit of absorbed radiation dose equal to 10⁻¹⁵ grays (Gy). The gray (Gy) is the standard SI unit used to measure the amount of ionizing radiation energy absorbed per kilogram of matter. One femtogray, therefore, represents a quadrillionth (0.000000000000001) of a gray. This unit is extremely small and is primarily used in theoretical research, nanodosimetry, or highly sensitive radiation studies where even the smallest levels of energy absorption can have measurable effects on microscopic or molecular systems. While real-world applications like medical imaging or radiation therapy use much larger units such as milligray (mGy) or gray (Gy), the femtogray can help researchers simulate or analyze interactions of radiation with DNA, proteins, or other cellular components. Although it is impractical for most everyday uses due to its tiny scale, the femtogray plays a valuable role in scientific fields requiring ultra-precise radiation dose measurements. It demonstrates how finely scientists can scale radiation measurements to better understand the effects of energy on matter at the smallest biological or atomic levels.