The equivalent dose (H_T) is a measure of the radiation dose to tissue where an attempt has been made to allow for the different relative biological effect of different types of ionizing radiation. Equivalent dose is therefore a less fundamental quantity than radiation absorbed dose, but is more biologically significant. Equivalent dose has units of sieverts. Another unit, Röntgen equivalent man (REM or rem), is still in common use in the US, although regulatory and advisory bodies are encouraging transition to sieverts (1 REM = 1/100 sievert.) ^[1]

Equivalent dose (H_T) is calculated by multiplying the absorbed dose to the organ or tissue (D_T) with the radiation weighting factor, w_R. This factor is selected for the type and energy of the radiation incident on the body, or in the case of sources within the body, emitted by the source. The value of w_R is 1 for x-rays, gamma rays and beta particles, but higher for protons, neutrons, alpha particles etc.

Where H_T,R = equivalent dose to tissue T from radiation R

D_T,R = absorbed dose D (in grays) to tissue T from radiation R

References

• ICRP. ICRP Publication 60: 1990 Recommendations of the International Commission on Radiological Protection. Elsevier Science Pub Co (April 1, 1991). ISBN 0-08-041144-4.

See also

• Ionizing radiation units
• Rad (unit)
• Gray (unit)
• Counts per minute
• Curie
• Becquerel
• Roentgen
• Röntgen equivalent man
• Sievert