Medical Physics ABR part 1 (2026/2027)
Questions And Answers Graded A+
What is the relationship between the photoelectric effect and Z?
Proportional to Z^3
How is the Compton effect dependent on Z?
Independent of Z, only dependent on electron density
What is the relationship between pair production and Z?
proportional to Zln(E)
What isodose line is SRS therapy prescribed to for LINAC based treatments?
70% isodose line
What isodose line is SRS therapy using gamma knife prescribed to?
50%
,How much of the central axis dose do physical and dynamic wedges scatter?
physical- 2.5%<br>Dynamic- 1.0%
Are electron beams a spectrum or mono energetic?
monoenergetic
What is the therapeutic depth for electrons?
R80
What is the occupational limit for 1 year?
50 mSv
What is the occupational limit for a pregnant radiation worker over the duration of
their pregnancy?
5 mSv
As field size increases, PDD ( increases or decreases) due to what?
PDD Increases because scatter increases
Scatter at 1m from a phantom is what fraction of the primary beam?
,1/1000
As SSD increases, PDD (increases or decreases) due to what?
increases due to inverse square
what is the maximum energy of lateral scatter from a photon beam?
0.511 MeV
What is the maximum energy backscattered from a photon beam?
0.255 MeV
What is the dose limit to the public in 1 year?
1 mSv
At what energy do neutrons need to be accounted for in shielding calculations?
10 MV
What is the approximate energy of neutrons produced in photo nuclear
interactions?
, 2 MeV
What is the limit for leakage?
1/1000 of central beam axis value
What energy are neutrons at the entrance of the vault?
100 keV this is the most dangerous because Wr=20
What is the average radiation exposure to someone in the US?
4-5 mSv / Year <br>
What are the sources of background radiation exposure in the US? (5)
Medical, Radon, ingested isotopes, isotopes occurring naturally, and cosmic rays
What is the k-edge of lead?
88 keV
What is the k-edge of iodine?
33 keV
Questions And Answers Graded A+
What is the relationship between the photoelectric effect and Z?
Proportional to Z^3
How is the Compton effect dependent on Z?
Independent of Z, only dependent on electron density
What is the relationship between pair production and Z?
proportional to Zln(E)
What isodose line is SRS therapy prescribed to for LINAC based treatments?
70% isodose line
What isodose line is SRS therapy using gamma knife prescribed to?
50%
,How much of the central axis dose do physical and dynamic wedges scatter?
physical- 2.5%<br>Dynamic- 1.0%
Are electron beams a spectrum or mono energetic?
monoenergetic
What is the therapeutic depth for electrons?
R80
What is the occupational limit for 1 year?
50 mSv
What is the occupational limit for a pregnant radiation worker over the duration of
their pregnancy?
5 mSv
As field size increases, PDD ( increases or decreases) due to what?
PDD Increases because scatter increases
Scatter at 1m from a phantom is what fraction of the primary beam?
,1/1000
As SSD increases, PDD (increases or decreases) due to what?
increases due to inverse square
what is the maximum energy of lateral scatter from a photon beam?
0.511 MeV
What is the maximum energy backscattered from a photon beam?
0.255 MeV
What is the dose limit to the public in 1 year?
1 mSv
At what energy do neutrons need to be accounted for in shielding calculations?
10 MV
What is the approximate energy of neutrons produced in photo nuclear
interactions?
, 2 MeV
What is the limit for leakage?
1/1000 of central beam axis value
What energy are neutrons at the entrance of the vault?
100 keV this is the most dangerous because Wr=20
What is the average radiation exposure to someone in the US?
4-5 mSv / Year <br>
What are the sources of background radiation exposure in the US? (5)
Medical, Radon, ingested isotopes, isotopes occurring naturally, and cosmic rays
What is the k-edge of lead?
88 keV
What is the k-edge of iodine?
33 keV
