The radiation dose unit Gray (Gy) measures:

• A Biological effectiveness of radiation weighted for tissue sensitivity
• B Exposure dose in air measured in Roentgens
• C Absorbed energy per unit mass of tissue (1 Gy = 1 J/kg) ✓
• D Effective dose accounting for radiation quality and tissue weighting factors

Explanation

The Gray (Gy) is the SI unit of absorbed radiation dose, defined as the absorption of 1 joule of energy per kilogram of matter (1 Gy = 1 J/kg). It measures only energy deposition, regardless of radiation type or tissue type. The Sievert (Sv) accounts for biological effectiveness — it equals absorbed dose in Gy multiplied by radiation weighting factor (WR: 1 for X-rays/gamma, 20 for alpha particles) and by tissue weighting factor for effective dose. Roentgen is the old unit of exposure (ionization in air). Effective dose (Sv) is used for radiation protection calculations comparing risks across different exposure scenarios.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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