Gray
Pronunciation: gray
Also written as: Gy — Gray
Standard unit of absorbed radiation dose, abbreviated as Gy, replacing the older unit rad.
Full Definition
The Gray (Gy) is the International System of Units (SI) standard for measuring absorbed radiation dose, defined as the absorption of one joule of radiation energy per kilogram of matter. One Gray equals 100 rad (the older unit). In clinical oncology, radiation doses are typically prescribed in Gray or centigray (cGy), where 1 Gy = 100 cGy. Total treatment doses commonly range from 20-80 Gy depending on treatment intent, tumor type, and location. The Gray specifically measures absorbed dose, distinct from equivalent dose (measured in Sieverts) which accounts for biological effectiveness.
Usage
Usage note: Always capitalize when abbreviated as Gy. Distinguish from centigray (cGy) and older rad unit.
In Context
- "The total prescribed dose was 60 Gray delivered in 30 fractions." — Radiation therapy prescription
- "Spinal cord dose was limited to a maximum of 45 Gy to prevent myelopathy." — Treatment planning document