Quantifying Dose Flashcards
What is the relationship of KERMA to dose?
KERMA is the kinetic energy released from a proton to an electron (= the kinetic energy of a charged particles released by a photon in a mass ‘m’). Dose is the damage done by the electron to surrounding medium.
What is the linear attenuation coefficient?
(u) is the fraction of photons removed per path length (from scattering or transfer of energy). When normalized to density, you get the mass energy transfer coefficient
What are the components of KERMA?
The electrons released delivery dose by collisions (Kc) and by radiative energy released (Kr). Kr is a small number and contributes minimally to dose.
What are the weighting factors for conservative dose equivalents?
photons = 1 protons/pions = 2 alpha particles = 20 fast neutrons = 20 slow neutrons = 2.5
How does an ion chamber measure kerma?
Exposure is the kerma released per mass of air. As a photon traverses an air cavity, it creates ion pairs. These ions are then attracted to opposite plates, where an electrometer measures the total charge produced. The total charge per unit of air = C/kg. 1 Roentgen = 2.58 e-4 C/kg air.
What is the Bragg-Gray Cavity theory?
For therapeutic photons (>3MeV), exposure cannot be directly measured due to the long range of secondary electrons in air. If you embed a chamber (cavity) in a medium, and that is small enough to not alter the distribution of electrons, you CAN measure dose based on exposure.
How does a TLD work?
The thermoluminescent diode (TLD) is exposed and cumulative radiation is stored in a crystal (ionizing radiation causes the electrons to a higher energy state and are trapped in impurities in the lattice). Later as the crystal is heated/cooled, the electrons drop back down and release photons.
How does an OSLD work?
The optically stimulated luminescence dosimeter (OSLD) operates on the same concept of a TLD, but instead of heating the crystals, they are stimulated with a laser to release energy.
What is Fricke gel and how does it work?
Fe2+ ions are oxidized by radiation to Fe3+. The concentration of 3+ ions are measured by spectrophotometry
How do solid state diodes work?
Impurities in the silicon wafers allow for “electron-rich” and “hole” areas. When irradiated, the middle zone splits into electrons and ‘holes’. Each migrates to their opposite side, modulating an electric current which can be measured.
