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KEY FACTS
Clinical Implications
TERMINOLOGY
Definitions
- Radiation intensity
- Roentgen (R) [non-Standard International (SI) units]; as measured with ionization chamber in milliroentgen per hour (mR/hr)
- Radiation intensity required to produce ionization charge of 0.000258 coulombs per kg of air (SI units)
- Absorbed dose
- Total amount of energy deposited in material
- Any type of radiation, any radiation intensity, any material
- Expressed as radiation absorbed dose (rad) (non-SI units), or gray (Gy) (SI units)
- 100 rads = 1 Gy; 1 rad = 10 mGy
- 1 rad = absorption of 100 ergs per g of tissue
- In nuclear medicine, this depends on many factors
- t1/2 of radiopharmaceutical
- Biological t1/2 of radiopharmaceutical
- Percentage taken up by body and differential uptake in organs
- Type of radiation emitted by radiopharmaceutical
- Absorbed dose for different nuclear medicine studies is estimated based on biodistribution studies in animals
- Total amount of energy deposited in material
- Equivalent dose
- Amount of radiation dose weighted based on damaging effects of type of radiation on tissue
- Accounts for differences in types of radiation type and intensity
- Based on relative biological effectiveness (RBE): Compares dose of standard radiation that yields biological response to dose of different radiation to produce similar biological response
- e.g., alpha particle with mass and charge (weighting factor Q of 20) will do more damage than gamma photon without mass or charge (weighting factor Q of 1)
- Measured in roentgen equivalent man (rem) (non-SI units), or sievert (Sv) (SI units)
- 100 rem = 1 Sv; 1 rem = 10 mSv
- rem = rad x weighting factor (Q)
- Amount of radiation dose weighted based on damaging effects of type of radiation on tissue
- Effective dose
- Equivalent dose while accounting for tissue/organ sensitivity and specific damage from radiation
- Tissue-weighted sum of equivalent doses in all tissues/organs of body
- e.g., tissue weighting factor (Wt) is high for breast tissue at 0.12 (12%) but low for brain tissue at 0.01 (1%); tissue weighting factors summed for all organs in body should add up to 1 (100%)
- Measured in rem (non-SI units) or Sv (SI units)
- Useful in estimating long-term biological risks to population from radiation exposure
- Direct effects
- Primarily from particulate and charged radiation (alpha, beta) where radiation directly damages cell
- Indirect effects
- Primarily from gamma and x-ray photons (no mass or charge) that primarily cause chemical changes from interactions with water and other molecules that lead to secondary chemical changes and indirect cell damage
- Radiation intensity
CLINICAL IMPLICATIONS
Molecular Effects of Radiation
Deterministic Effects of Radiation
Stochastic Effects of Radiation
Dose-Response Models
Radiation Epidemiology
Internal Radiation Dosimetry
Selected References
- NCRP Report No. 184: Medical Radiation Exposure of Patients in the United States, 2019
- Hall E et al: Radiobiology for the Radiologist. 8th ed. Wolters Kluwer, 2018
- NCRP Report No. 160: Ionizing Radiation Exposure of the Population of the United States, 2009
- Cherry et al: Physics in Nuclear Medicine. 3rd ed. Saunders, 2003
- Bolus NE: Basic review of radiation biology and terminology. J Nucl Med Technol. 29(2):67-73; test 76-7, 2001
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References
Tables
Tables
KEY FACTS
Clinical Implications
TERMINOLOGY
Definitions
- Radiation intensity
- Roentgen (R) [non-Standard International (SI) units]; as measured with ionization chamber in milliroentgen per hour (mR/hr)
- Radiation intensity required to produce ionization charge of 0.000258 coulombs per kg of air (SI units)
- Absorbed dose
- Total amount of energy deposited in material
- Any type of radiation, any radiation intensity, any material
- Expressed as radiation absorbed dose (rad) (non-SI units), or gray (Gy) (SI units)
- 100 rads = 1 Gy; 1 rad = 10 mGy
- 1 rad = absorption of 100 ergs per g of tissue
- In nuclear medicine, this depends on many factors
- t1/2 of radiopharmaceutical
- Biological t1/2 of radiopharmaceutical
- Percentage taken up by body and differential uptake in organs
- Type of radiation emitted by radiopharmaceutical
- Absorbed dose for different nuclear medicine studies is estimated based on biodistribution studies in animals
- Total amount of energy deposited in material
- Equivalent dose
- Amount of radiation dose weighted based on damaging effects of type of radiation on tissue
- Accounts for differences in types of radiation type and intensity
- Based on relative biological effectiveness (RBE): Compares dose of standard radiation that yields biological response to dose of different radiation to produce similar biological response
- e.g., alpha particle with mass and charge (weighting factor Q of 20) will do more damage than gamma photon without mass or charge (weighting factor Q of 1)
- Measured in roentgen equivalent man (rem) (non-SI units), or sievert (Sv) (SI units)
- 100 rem = 1 Sv; 1 rem = 10 mSv
- rem = rad x weighting factor (Q)
- Amount of radiation dose weighted based on damaging effects of type of radiation on tissue
- Effective dose
- Equivalent dose while accounting for tissue/organ sensitivity and specific damage from radiation
- Tissue-weighted sum of equivalent doses in all tissues/organs of body
- e.g., tissue weighting factor (Wt) is high for breast tissue at 0.12 (12%) but low for brain tissue at 0.01 (1%); tissue weighting factors summed for all organs in body should add up to 1 (100%)
- Measured in rem (non-SI units) or Sv (SI units)
- Useful in estimating long-term biological risks to population from radiation exposure
- Direct effects
- Primarily from particulate and charged radiation (alpha, beta) where radiation directly damages cell
- Indirect effects
- Primarily from gamma and x-ray photons (no mass or charge) that primarily cause chemical changes from interactions with water and other molecules that lead to secondary chemical changes and indirect cell damage
- Radiation intensity
CLINICAL IMPLICATIONS
Molecular Effects of Radiation
Deterministic Effects of Radiation
Stochastic Effects of Radiation
Dose-Response Models
Radiation Epidemiology
Internal Radiation Dosimetry
Selected References
- NCRP Report No. 184: Medical Radiation Exposure of Patients in the United States, 2019
- Hall E et al: Radiobiology for the Radiologist. 8th ed. Wolters Kluwer, 2018
- NCRP Report No. 160: Ionizing Radiation Exposure of the Population of the United States, 2009
- Cherry et al: Physics in Nuclear Medicine. 3rd ed. Saunders, 2003
- Bolus NE: Basic review of radiation biology and terminology. J Nucl Med Technol. 29(2):67-73; test 76-7, 2001
