W/L Ch 25 Electron Beam Quiz Flashcards
Which processes are responsible for electron interactions with matter?
I. Collisional processes
II. Radiation processes
III. Gradient processes
a. I and II
b. I and III
c. II and III
d. I, II, and III
a. I and II
What are electrons scattered with enough energy to cause further ionization and excitations in other atoms?
a. Alpha particles
b. Beta particles
c. Delta rays
d. Gamma rays
c. Delta rays
Which processes are responsible for the majority of energy loss for electron energy ranges useful in radiation therapy?
I. Collisional processes
II. Radiation processes
III. Gradient processes
a. I only
b. II only
c. III only
d. I and II
a. I only
Which treatment energy for electrons is most likely to use a scanning beam technique rather than a scattering foil?
a. 4 MeV
b. 12 MeV
c. 20 MeV
d. 25 MeV
d. 25 MeV
Scanning beams are especially useful above 25 MeV, when the thickness of the required scattering foils would result in difficulties with their mechanical size and would cause problems with electron contamination.
Which technique is most likely to result in photon contamination of the electron beam?
a. Use of an electron gun
b. Use of a bending magnet
c. Use of a scattering foil
d. Use of a scanning beam
c. Use of a scattering foil
What effect will an increase in the nominal energy of an electron beam have on the depth of the 80% isodose line?
a. Increase
b. Decrease
c. Remain the same
d. Dose dependence
a. Increase
Interactions with which of the following is not a cause of photon contamination of an electron beam?
a. Scattering foils
b. Collimators
c. Air
d. Patient
d. Patient
Given a mean energy of an electron beam is 6 MeV, what is the depth of the 50% isodose line?
a. 2.5 mm
b. 14.4 mm
c. 2.5 cm
d. 14.4 cm
c. 2.5 cm
What will be the energy of an electron beam at a depth of 4 cm that had a surface energy of 16 MeV?
a. 4 MeV
b. 12 MeV
c. 14 MeV
d. 16 MeV
b. 12 MeV
?
What is the practical range of a 25-MeV electron beam?
a. 12.5 cm
b. 12.5 mm
c. 50 cm
d. 50 mm
a. 12.5 cm
Practical range
E = MeV/2.
E = 25 MeV / 2
= 12.5 cm
What is the depth of the 80% isodose line of a 15-MeV electron beam?
a. 3 cm
b. 3.75 cm
c. 5 cm
d. 7.5 cm
c. 5 cm
80% isodose = MeV / 3
or = MeV x 1/3
15 MeV x 1/3
= 5 cm
What is the depth of the 90% isodose line of a 9-MeV electron beam?
a. 2.25 cm
b. 3 cm
c. 4.5 cm
d. 9 cm
a. 2.25 cm
90% isodose = MeV / 4
or = MeV x 1/4
9 MeV x 1/4
= 2.25 cm
Which electron beam’s diameter (field size) is most likely to have an effect on a 20-MeV beam’s surface dose and percent depth dose?
a. 5 cm
b. 10 cm
c. 15 cm
d. 20 cm
a. 5 cm
There is little effect of field size on both surface dose and percent depth dose of electron beams, provided the fields are of sufficient size. The rule is that the electron beam’s diameter (field size) in centimeters should not be less than the practical range.
p 541
Which electron beam energy is most likely to under-dose at the surface?
a. 9 MeV
b. 12 MeV
c. 16 MeV
d. 20 MeV
a. 9 MeV
Which of the following is not an application of bolus when used with electron beams?
a. Increase surface dose
b. Tissue compensator
c. Shape isodose distributions
d. Increase the effective energy at depth
d. Increase the effective energy at depth
What effect will an increase in the energy of an electron beam have on the lateral bulge of the 80% isodose line?
a. Increase
b. Decrease
c. Remain the same
d. Dose dependence
b. Decrease
According to the Association of Physicists in Medicine (AAPM) Task Group 25 report, what distance is considered an extended source-skin distance (SSD) for electron beams?
a. Greater than 100 cm SSD
b. Greater than 110 cm SSD
c. Greater than 115 cm SSD
d. Greater than 130 cm SSD
c. Greater than 115 cm SSD
Which process is responsible for the majority of energy loss for electron energy ranges useful in radiation therapy?
I. Effective point source method
II. Virtual source method
a. I only
b. II only
c. I and II
d. Neither I nor II
c. I and II
What thickness of lead is necessary to adequately shield a 9-MeV electron beam?
a. 3 cm
b. 3.6 cm
c. 4.5 cm
d. 5.4 cm
c. 4.5 cm
“The thickness of lead in millimeters required for shielding is approximately given by the energy in MeV divided by 2.”
9/2
What thickness of Lipowitz alloy is necessary to adequately shield a 9-MeV electron beam?
a. 3 cm
b. 3.6 cm
c. 4.5 cm
d. 5.4 cm
d. 5.4 cm
“The thickness of lead in millimeters required for shielding is approximately given by the energy in MeV divided by 2.” The thickness of Lipowitz alloy (Cerrobend) required may be obtained by multiplying the thickness in lead indicated by the rule of thumb by 1.2.
9/2
= 4.5
4.5 x 1.2
= 5.4 cm
What is the danger to tissue in front of an internal shield when used with electron beams therapy?
a. Photon contamination
b. Under dosing
c. Electron backscatter
d. Infection
c. Electron backscatter
Surface dose values for electron beams in the 6- to 20-MeV range vary from __________.
a. 100% to 105%
b. 95% to 100%
c. 80% to 90%
d. 70% to 80%
c. 80% to 90%
To produce a therapeutically useful electron beam, the stream of electrons leaving the electron gun must contact the ___________ before exiting the gantry head.
a. target
b. scattering foil
c. flattening filter
d. mirror and bulb assembly
b. scattering foil
As the mean energy of an electron beam increases, the _________________________.
a. surface dose decreases
b. surface dose increases
c. percent depth dose decreases
d. practical range depth decreases
b. surface dose increases
Which of the following is one very important consideration during the use of internal shields when administering electron therapy?
a. Shielding materials become radioactive
b. Dose to tissues directly in front of the shield is increased
c. Internal shields need to be secured by suturing
d. Shielding material thickness is found by MeV/3
b. Dose to tissues directly in front of the shield is increased
