Dose and Nuclear Medicine Flashcards
2 forms of radiation
indirect/direct action
indirect action
electron interacts with a water molecule to produce a radical which damages the DNA
direct action
electron interacts directly with DNA
Radiation dose definition
energy deposited in matter by ionizing radiation per unit mass
Energy fluence
fluence (change in the number of particles with respect to change in unit area) x energy of the particle in a monoenergetic beam
mass energy transfer coefficient
product of the mass attenuation coefficient and the fraction of energy transferred to the patient as a result of the type of interaction
locally transferred meaning
absorbed by a local region
Difference between KERMA and Dose
KERMA : Total energy transferred to a local region vs Total energy absobred by a local region
Weighting by tissue
S_v (sievert / dose absorbed by tissue) = Dose x Weighting by tissue
imaging particles
gamma rays
therapeutic particles
electrons
Decay processes involved in gamma imaging
Beta decay
Beta+ decay
Electron capture
Transition processes
unstable nuclei with gamma emissions
isomeric transition
Beta- decay
neutron rich isotope
beta- is emitted
charge must be conserved
proton is therefore emitted
beta- decay where is the excedent energy transferred to
gamma rays
beta+ decay
proton-rich isotope to stabilise the n/p ratio (increase)
neutron is emitted
positron is emitted in the form of gamma rays
what happens to beta+ particle
loses energy to surrounding tissue
annihiates with an electron
opposite charge
produces 2 photons (pair production)
Electron capture
orbital electron is captured by the nucleus and combines with a proton to become a neutron
Change in number of electrons due to electron capture
-1 electron
vacancy in the atomic shell filled by another electron
photoelectric effect
energy released when electron falls by energy levels in the form of x-ray
Isomeric transition
decay into an unstable state for a while
which then decays to another state where a gamma ray is emitted
why does beta produce dose
low energy lose it quickly and stop in the body
properties of a useful isotope
emit gamma or x rays only as those are what appear on the image
medium energy emissions
appropriate half life (few minutes - hours )
easily produced
