# Equivalent dose and effective dose (sievert)

Source: https://nuclide.cc/terms/equivalent-dose/  
Nuclide record `equivalent-dose` (Term). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

A way of converting a physical radiation dose into a single number for comparing radiation risk across different types of radiation and different organs. It is used for radiation-protection purposes, not for prescribing cancer treatment doses.

## Summary

Equivalent dose (H) adjusts the absorbed dose in an organ or tissue (measured in gray) by a radiation weighting factor (wR) that reflects how biologically damaging a given type of radiation is, compared with photons or beta particles of the same absorbed dose: H_T = sum over R of wR times D_T,R. Current ICRP values are wR = 1 for photons, electrons and beta particles, wR = 2 for protons, and wR = 20 for alpha particles, reflecting alpha particles' much higher biological potency per unit of physical dose. Equivalent dose is expressed in sievert (Sv), the same unit (J/kg) as gray but with a different name to signal that a biological weighting has been applied.

Effective dose (E) goes one step further, multiplying the equivalent dose to each organ by a tissue weighting factor (wT, which sums to 1 across the whole body) that represents that organ's relative contribution to overall cancer and heritable-disease risk from uniform whole-body irradiation, then summing across organs. Effective dose, also in sievert, is the standard quantity used in radiation protection to compare the stochastic (cancer-risk) burden of different exposures, for example a diagnostic PET/CT scan versus natural background radiation.

These are protection quantities developed by the ICRP for population-level risk management and regulatory dose limits; they are not used to prescribe or evaluate radiopharmaceutical therapy, where the organ-specific absorbed dose in gray (via the MIRD formalism), sometimes adjusted for relative biological effectiveness rather than the fixed regulatory wR, is what guides treatment planning.

## Fields

- Kind: Term
- Last checked: 2026-09-22

## Sources

- ICRP: The Use of Dosimetric Quantities in Radiological Protection: https://www.icrp.org/docs/physics_icrp_found_doc_for_web_consult.pdf
- ICRPaedia: Absorbed, Equivalent, and Effective Dose: https://icrpaedia.org/Absorbed,_Equivalent,_and_Effective_Dose

## Connected records

- terms: [Absorbed dose and the gray (Gy)](https://nuclide.cc/terms/absorbed-dose-term/), [Linear energy transfer (LET)](https://nuclide.cc/terms/linear-energy-transfer/), [Relative biological effectiveness (RBE)](https://nuclide.cc/terms/relative-biological-effectiveness/)
- technologies: [In vivo dosimetry and patient-specific quality assurance](https://nuclide.cc/technologies/in-vivo-dosimetry/), [Radioligand dosimetry](https://nuclide.cc/technologies/radioligand-dosimetry/)

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