- Determining the quality of radiation exposure or dose is termed dosimetry.
- Dose is used to describe amount of energy absorbed per unit mass at site of interest.
- Radiation absorbed dose (D).
- Equivalent dose (HT).
- Effective dose (E).
- Collective effective dose or collective dose.
- Dose rate.
- Exposure or radioactivity.
This is the measure of amount of energy absorbed from the radiation beam per unit mass of tissue.
- S I unit- Gray, (Gy) measured in joules/kg.
- Sub unit- milligray, (mGy)(x10-3).
- Original unit: rad, measured in ergs/g.
- Conversion I Gy =100 rads.
It is used to compare the biologic effects of different types of radiation to a tissue or organ.
Equivalent dose= Radiation absorbed dose (D) X Radiation weighting factor (WR)
- S I unit- Sievert (Sv).
- Sub unit:
- millisievert (mSv) X10-3
- microsievert (µSv)X 10-6
- Original unit- rem.
- Conversion 1 Sievert = 100rems.
- The effective dose is used to estimate the risk in humans.
- The international commission on radiological protection (ICRP) has allocated each tissue a numerical value known as tissue weighting factor based on its radio sensitivity.
- Greater the risk, the higher tissue weighting factor.
- Effective dose (E) = Equivalent dose (HT) X Tissue weighting factor(WR).
- S I unit- Sievert (Sv).
- Sub unit-millisievert (mSv).
- This measure is used when considering the total effective dose to a population, from a particular investigation or a source of radiation.
- Collective dose= effective dose(E) X Population
- S I unit = man- sievert (man-sv)
Exposure is the measure of radiation quality, the capacity of radiation to ionized air.
- S I unit= Air kerma.
- Traditional unit: Roentgen(R).
- Kerma measures the kinetic energy transferred from photons to electrons and is expressed in units of dose (Gy), where 1 Gy equals 1 joule/kg.
- Kerma is the sum of the initial kinetic energies of all ionizing radiation (neutrons and photons) in a sample of matter, divided by the mass of the sample.
- It is the measurement of radioactivity (A) describes the decay rate of a sample of radioactive material.
- S I unit= Becquerel (Bq)
- The traditional unit is the curie (Ci).
- 1Bq=2.7×10-11 Ci.
- 1Ci=3.7×1010 Bq.
- Goaz PW, White SC Radiation physics. Book of oral radiology, principles and interpretation 2nd edition 1990;41-43.
- White SC, Pharaoh MJ Physics of ionizing radiation. Book of oral radiology principles and interpretations 5th edition 2009;20-21.
- Whaites E Dose units and dosimetry. Book of Essentials of dental radiography and radiology 3rd edition 2002;25-27.