link
Bookmarks
Radiation Biology and Dose
Angela P. Bruner, PhD, DABR; Umesh D. Oza, MD
To access 4,300 diagnoses written by the world's leading experts in radiology, please log in or subscribe.Log inSubscribe

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/h)
        • 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, 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 estimated based on biodistribution studies in animals
      • 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 R 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)
      • 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) 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 & 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

    CLINICAL IMPLICATIONS

    • Molecular Effects of Radiation

      • Deterministic Effects of Radiation

        • Stochastic Effects of Radiation

          • Dose-Response Models

            • Radiation Epidemiology

              • Internal Radiation Dosimetry

                Selected References

                1. Cherry et al: Physics in Nuclear Medicine, 4th edition. Saunders, 2012
                2. Hall E: Radiobiology for the Radiologist. Lippincottt Williams & Wilkins, 2011
                3. Mahesh M: NCRP Report Number 160: its significance to medical imaging. J Am Coll Radiol. 6(12):890-2, 2009
                4. Bolus NE: Basic review of radiation biology and terminology. J Nucl Med Technol. 29(2):67-73; test 76-7, 2001
                5. Society of Nuclear Medicine and Molecular Imaging, PET Center of Excellence. http://www.snmmi.org/AboutSNMMI/PetCenterOfExcellence.aspx?ItemNumber=6558. Accessed June 2017.
                6. Axumin (Fluciclovine F-18) FDA Package Insert. http://www.axumin.com/pdf/formulary_information/Dosing_Admin_03%20FINAL.pdf. Created August 2016. Accessed June 2017.
                Related Anatomy
                Loading...
                Related Differential Diagnoses
                Loading...
                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/h)
                      • 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, 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 estimated based on biodistribution studies in animals
                    • 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 R 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)
                    • 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) 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 & 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

                  CLINICAL IMPLICATIONS

                  • Molecular Effects of Radiation

                    • Deterministic Effects of Radiation

                      • Stochastic Effects of Radiation

                        • Dose-Response Models

                          • Radiation Epidemiology

                            • Internal Radiation Dosimetry

                              Selected References

                              1. Cherry et al: Physics in Nuclear Medicine, 4th edition. Saunders, 2012
                              2. Hall E: Radiobiology for the Radiologist. Lippincottt Williams & Wilkins, 2011
                              3. Mahesh M: NCRP Report Number 160: its significance to medical imaging. J Am Coll Radiol. 6(12):890-2, 2009
                              4. Bolus NE: Basic review of radiation biology and terminology. J Nucl Med Technol. 29(2):67-73; test 76-7, 2001
                              5. Society of Nuclear Medicine and Molecular Imaging, PET Center of Excellence. http://www.snmmi.org/AboutSNMMI/PetCenterOfExcellence.aspx?ItemNumber=6558. Accessed June 2017.
                              6. Axumin (Fluciclovine F-18) FDA Package Insert. http://www.axumin.com/pdf/formulary_information/Dosing_Admin_03%20FINAL.pdf. Created August 2016. Accessed June 2017.