Radiation Therapy Exam A+ Pass
Latest Update
What are the steps to planning a CT Simulation - Answer- Rx to a point at depth,
Assume we are made of water, Open fields, Monitor Unit Calcs
What is the primary photon interaction used for calculating dose in targets with photon
energy > 1 MeV - Answer- Compton scattering
What is the assumption in compton scattering/klein nishina total cross section - Answer-
Assume the electron struck by the incoming photon is unbound and stationary (free
electron) is cross section is independent of Z, need to look at electron density
Based on Klein Nishina Total Cross section, what does water equivalent really mean? -
Answer- Means electron density equivalent (electrons/cm^3
How is electron density calculated from mass density and atomic composition - Answer-
calculated with rho e= rho m * Na * (Z/A)
Compton scattering is almost independent of - Answer- Z
What are hounsfield units? - Answer- They are known as CT numbers- the grey scale
value
Name 3 hounsfield parameters and what their values are - Answer- HUwater= 0, HU
air= -1000, HU bone=+700
What should be done if you get a new CT scanner or if it goes significant survicing
where the effective energy changes? - Answer- The CT numbers vs the Relative
Electron density curve should be measured
What equation should you use to re measure the CT scanner? - Answer- Hounsfield
one utissue-uwater/uwater
With the hounsfield equation, the energy ________________________, as the
interactions shift from photoelectric to ______________ - Answer- increases as it shifts
to compton scattering
Difference between CT and CT sim - Answer- CT is used to identify malignancies in
diagnostic but the rad onc CT sim is for a simulation to obtain geometric accuracy of the
are that woul dbe treated. You would match the CT sim with diagnostic imaging to help
with target deliniation
Latest Update
What are the steps to planning a CT Simulation - Answer- Rx to a point at depth,
Assume we are made of water, Open fields, Monitor Unit Calcs
What is the primary photon interaction used for calculating dose in targets with photon
energy > 1 MeV - Answer- Compton scattering
What is the assumption in compton scattering/klein nishina total cross section - Answer-
Assume the electron struck by the incoming photon is unbound and stationary (free
electron) is cross section is independent of Z, need to look at electron density
Based on Klein Nishina Total Cross section, what does water equivalent really mean? -
Answer- Means electron density equivalent (electrons/cm^3
How is electron density calculated from mass density and atomic composition - Answer-
calculated with rho e= rho m * Na * (Z/A)
Compton scattering is almost independent of - Answer- Z
What are hounsfield units? - Answer- They are known as CT numbers- the grey scale
value
Name 3 hounsfield parameters and what their values are - Answer- HUwater= 0, HU
air= -1000, HU bone=+700
What should be done if you get a new CT scanner or if it goes significant survicing
where the effective energy changes? - Answer- The CT numbers vs the Relative
Electron density curve should be measured
What equation should you use to re measure the CT scanner? - Answer- Hounsfield
one utissue-uwater/uwater
With the hounsfield equation, the energy ________________________, as the
interactions shift from photoelectric to ______________ - Answer- increases as it shifts
to compton scattering
Difference between CT and CT sim - Answer- CT is used to identify malignancies in
diagnostic but the rad onc CT sim is for a simulation to obtain geometric accuracy of the
are that woul dbe treated. You would match the CT sim with diagnostic imaging to help
with target deliniation
