What's the difference between absorbed dose and equivalent dose?

Absorbed dose (Gy) measures energy deposited per mass—pure physics. Equivalent dose (Sv) = absorbed dose × radiation weighting factor, accounting for biological effectiveness. Alpha particles cause 20× more damage than X-rays per gray, so 1 Gy alpha = 20 Sv.

Why is radiation therapy given in fractions?

Fractionation (e.g., 2 Gy/day for 30 days) allows healthy tissue to repair between doses while tumor tissue, with poorer repair mechanisms, accumulates damage. Total dose of 60 Gy would be lethal if given at once, but fractionated delivery is tolerable and effective.

How much radiation causes acute sickness?

Acute radiation syndrome begins around 0.5-1 Gy whole-body dose. Nausea starts at 1 Gy. Without treatment, 50% mortality occurs at 3-4 Gy (LD50/30). Above 6 Gy, survival without heroic intervention is unlikely. Local doses (like in therapy) are different from whole-body.

جرعة الإشعاع الممتصة Converter

About Radiation Absorbed Dose Conversion

Absorbed dose measures the energy deposited by ionizing radiation per unit mass of material. Unlike exposure (which measures ionization in air), absorbed dose applies to any material—tissue, bone, metal, or plastic—and directly relates to potential biological damage. The same absorbed dose can have different effects depending on radiation type, which is why equivalent dose (sieverts) was developed for biological risk assessment. Absorbed dose tells you the pure physics: how much energy was deposited.

The SI unit is the gray (Gy), equal to one joule per kilogram, named after British radiobiologist Louis Harold Gray. The older unit rad (radiation absorbed dose) equals 0.01 gray or 1 centigray. Absorbed dose is fundamental to radiation therapy planning, industrial radiography safety, and accident dosimetry. Medical linear accelerators deliver precisely calibrated doses in grays to tumor volumes while minimizing dose to surrounding tissue.

Our converter handles all standard absorbed dose units used in medical physics and radiation protection.

Common Absorbed Dose Conversions

From	To	Multiply By
Gy	rad	100
rad	Gy	0.01
Gy	mGy	1,000
mGy	Gy	0.001
Gy	μGy	10⁶
Gy	cGy	100
cGy	Gy	0.01
rad	mrad	1,000

Absorbed Dose Unit Reference

Gray (Gy) – The SI unit of absorbed dose, equal to 1 joule of radiation energy deposited per kilogram of material. 1 Gy = 100 rad = 100 cGy. Named after Louis Harold Gray (1905-1965), a British physicist who developed the cavity ionization theory fundamental to radiation dosimetry. Typical radiation therapy delivers 1.8-2 Gy per fraction to tumors.

Centigray (cGy) – One-hundredth of a gray: 1 cGy = 0.01 Gy = 1 rad exactly. Widely used in radiation oncology because it conveniently equals the older rad unit, allowing continuity with historical treatment protocols. Many treatment planning systems report doses in cGy.

Milligray (mGy) – One-thousandth of a gray: 1 mGy = 0.001 Gy = 0.1 rad. The typical scale for diagnostic imaging doses: chest X-ray ~0.1 mGy, CT scan 10-30 mGy, fluoroscopy procedures may accumulate hundreds of mGy to specific organs.

Rad (radiation absorbed dose) – The traditional CGS unit of absorbed dose. 1 rad = 0.01 Gy = 1 cGy = 100 erg/g. Still encountered in older US regulations, historical records, and some industrial contexts. The name is an acronym for "radiation absorbed dose."

Microgray (μGy) – 10⁻⁶ Gy = 0.1 mrad. Used for very low doses such as environmental monitoring, background radiation measurements, and some dental X-rays.

Erg per gram (erg/g) – The fundamental CGS definition of absorbed dose. 1 rad = 100 erg/g; 1 Gy = 10,000 erg/g = 1 J/kg. Rarely used in practice but clarifies the physical meaning of absorbed dose.