(1)
University of Miami Sylvester Cancer Center, Miami, Florida, USA
Treatment planning is the central task for dosimetrists and is also a very important task for medical physicists. Planning skill and experience are the major standards in the job market for dosimetrists.
Readers are expected to be very familiar with TPS tools (e.g., contouring, BEV, wedges, EDW, MLC, bolus, blocks, IDLs, DVH, etc.), case-specific skills, optimization skills, and dose calculation algorithms (correction-based, model-based), as well as the principles standing behind those tools.
Intensity-modulated radiotherapy (IMRT) was developed after 3-dimensional conformal radiation therapy (3D-CRT) had been popularly applied. The primary goal for IMRT was to spare dose to normal tissue and hence significantly reduce normal tissue complication probability (NTCP). The implementation of IMRT was the key reason that the field of medical physics and dosimetry has been booming since the 1990s.
3.1 Isodose Curve Parameters and Isodose Distributions (Questions)
Quiz 1 (Level 2)
1.
A plot of the volume of a given structure receiving a certain dose or higher as a function of dose is the definition of?
A.
Differential DVH
B.
Cumulative integral DVH
C.
Dose volume histogram (DVH)
D.
Beam’s eye view
2.
Which of the following about dose volume histograms (DVH) are correct?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Provide quantitative information with regard to how much dose is absorbed in how much volume
II.
Are a great tool for evaluating a given plan or comparing competing plans
III.
Summarize the entire dose distribution into a single curve for each anatomic structure of interest
IV.
Display the area where hot spot is located
3.
Which of the following about isodose charts are correct?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Consist of a family of isodose curves.
II.
Isodose curves are usually drawn for equal increments of percent depth dose.
III.
Have lines that represent equal percentage depth dose for a particular field size and SSD at a specific plane in the tissue.
IV.
Give you specific hot spot location.
4.
Which of the following are correct according to the following DVH?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
Fig. 3.1.1 Courtesy of the University of Miami, Sylvester Cancer Center
I.
Line A, max dose is approximately 9 Gy.
II.
Line B, V20 Gy <20 % was achieved.
III.
Line C, 30 % of the volume receives at least 30 Gy.
IV.
Line D, Rx dose of 60 Gy (>95 % coverage) was not achieved.
5.
Based on the following graph, line B represents the oral cavity and the prescription dose is 60 Gy to a head and neck area. What percentage of the oral cavity received more than the prescribed dose (V60 Gy)?
Fig. 3.1.2 Courtesy of the University of Miami, Sylvester Cancer Center
A.
0 %
B.
20 %
C.
70 %
D.
96 %
6.
Which of the following dose volume histogram (DVH) has been found to be more useful and more commonly used?
A.
Differential
B.
Cumulative
C.
Isodose curve
D.
Beam’s eye view
7.
Which of the following scenarios will not include a DVH?
A.
3D conformal planning
B.
IMRT planning
C.
IMRT ARC planning
D.
Electron clinical setup
8.
Which of the following plans should contain a dose volume histogram (DVH) of the PTV and organs at risk?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
3D conformal planning
II.
HDR breast planning
III.
IMRT planning
IV.
Electron planning
9.
Which of the following isodose lines (IDLs) typically represent the field edge or border?
A.
100 % isodose line
B.
75 % isodose line
C.
50 % isodose line
D.
Cannot be identified
10.
Which of the following statements are true?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
When a composite plan is done, it is essential that the doses contributed by each plan be added together and a composite isodose distribution be displayed.
II.
When a composite plan is done, just the current plan isodose distribution is needed to be displayed on the contour and DVH.
III.
Isodose charts are produced by measuring the dose distribution in a water phantom.
IV.
A DVH is the only way to analyze a plan.
11.
In general, the ideal DVH for a treatment target like a PTV is?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
95 % of the volume to receive 100 % of the prescribed dose.
II.
50 % of the volume to receive 100 % of the prescribed dose.
III.
5 % of the volume should not receive more than 110 % of the prescribed dose.
IV.
5 % of the volume should receive more than 110 % of the prescribed dose.
12.
Which of the following about isodose curves are correct?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
They are lines passing through points of equal dose.
II.
They are expressed as a percentage of the dose at a reference point.
III.
They represent levels of absorbed dose.
IV.
They represent the hot spot location.
13.
The depth dose values of the isodose curves are typically normalized:
A.
I, II, and III.
B.
II and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
At 50 % of the prescribed dose
II.
At the point of the central axis
III.
At the point of maximum dose in any area of the field
IV.
At a fixed distance along the central axis in the irradiated medium
14.
Which of the following statements are true?
A.
The dose at depth is greatest on the central axis of the beam and gradually decreases toward the edges of the beam.
B.
The dose at any depth is lower on the central axis of the beam and gradually increases toward the edges of the beam.
C.
Near the field edges, the dose rate increases rapidly as a function of lateral distance from the beam axis.
D.
Isodose curves at specified depth are not of concern when defined physical penumbra.
15.
Horns are?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
High-dose areas near the surface in the periphery of the field
II.
Low-dose areas near the surface in the periphery of the field
III.
Are created by the flattening filter
IV.
Are created by the scatter in the body
16.
Which of the following statements is/are true?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
The field size is defined as the medial distance between the 50 % isodose lines at a reference depth.
II.
The field size is defined as the lateral distance between the 50 % isodose lines at a reference depth.
III.
The field-defining light is made to coincide with the 100 % isodose line of the radiation beam projected on a plane perpendicular to the beam axis.
IV.
The field-defining light is made to coincide with the 50 % isodose line of the radiation beam projected on a plane perpendicular to the beam axis.
17.
The following graph represents the:
A.
Isodose chart
B.
Isodose distribution
C.
Dose volume histogram
D.
Beam profile
Fig. 3.1.3 Courtesy of the University of Miami, Sylvester Cancer Center
18.
Which of the following parameters affect the isodose distribution?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Beam energy
II.
Source size, SSD, and SDD
III.
Collimation
IV.
Field size
19.
Which of the following statements are true?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
The depth of a given isodose curve increases with beam quality or energy.
II.
Lower-energy beams cause the isodose curves outside the field to bulge out.
III.
The isodose curves outside the primary beam are greatly distended in the case of orthovoltage radiation.
IV.
The isodose curves outside the primary beam are minimized for megavoltage beams as a result of predominantly forward scattering.
20.
Which of the following has the greatest influence in determining the shape of the isodose curves?
A.
Field size
B.
Flattening filter
C.
Source-to-skin distance (SSD)
D.
Beam energy
21.
The function of the flattening filter is?
A.
To reduce the penumbra of a therapy beam
B.
To measure and verify precise amounts of radiation to the patient
C.
To make the beam intensity distribution relatively uniform across the field
D.
To power high-energy linear accelerators
22.
The most commonly used isodose beam-modifying device is?
A.
Block
B.
Wedge
C.
Cut out
D.
Bolus
23.
Which of the following are correct about wedges?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Tilt the isodose curves toward the thin end of the wedge.
II.
Tilt the isodose curves toward the thicker end of the wedge.
III.
The degree of tilt depends on the slope of the wedge filter.
IV.
The degree of tilt depends on the position of the wedge (RT, LT, in or out).
24.
Match the following dose volume histogram.
A.
Differential DVH displayed in absolute dose
B.
Cumulative DVH displayed in absolute dose
C.
Cumulative DVH displayed in absolute volume
I.
Fig. 3.1.4 Courtesy of the University of Miami, Sylvester Cancer Center
II.
Fig. 3.1.5 Courtesy of the University of Miami, Sylvester Cancer Center
III.
Fig. 3.1.6 Courtesy of the University of Miami, Sylvester Cancer Center
25.
Which of the following DVHs is used to evaluate a particular volume for a critical structure?
A.
Differential DVH displayed in absolute dose
B.
Cumulative DVH displayed in absolute dose
C.
Cumulative DVH displayed in absolute volume
26.
The advantages of parallel opposed fields are?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Simplicity and reproducibility of the setup
II.
More homogeneous dose to the tumor than a single field
III.
Less chances of geometrical miss
IV.
Excessive dose to normal tissues and critical organs above and below the tumor
27.
The isodose uniformity distribution depends on?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Patient thickness
II.
Beam energy
III.
Beam flatness
IV.
Correct weighting
28.
Which of the following dose is used by NIST and/or an ADCL?
A.
Absolute dose
B.
Integral dose
C.
Relative dose
D.
Radiation dose
29.
Some strategies used to maximize dose to the tumor while minimizing dose to surrounding tissue are?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Increasing the number of fields
II.
Selecting appropriate beam direction
III.
Adjusting beam weights
IV.
Using appropriate beam energy
30.
What is an isocentric treatment technique?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
It consists of placing the isocenter of the machine at a depth within the patient and directing the beams from different directions.
II.
The distance of the source from the isocenter (SAD) remains constant irrespective of the beam direction.
III.
Source-to-skin distance (SSD) may change, depending on the beam direction and shape of the patient contour.
IV.
Isocenter is the point of intersection of the collimator axis and the gantry axis of rotation.
31.
For an isocentric treatment technique, the source-to-skin distance is?
A.
SSD = SAD − d
B.
SSD = SAD + d
C.
SSD = SAD/d
D.
SSD = SAD × d
32.
The lateral distance between two specified isodose curves at specified depth is used to estimate?
A.
Tissue lateral effect
B.
Transmission penumbra
C.
Physical penumbra
D.
Beam profile
33.
Outside the geometric limits of the beam and the penumbra, the dose variation is the result of?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Side scatter from the field
II.
Lateral scatter from the medium
III.
Leakage and scatter from the collimator
IV.
Leakage from the head of the machine
34.
Isodose charts can be measured by means of?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Ion chambers
II.
Solid-state detectors
III.
Radiographic films
IV.
Calorimeter
35.
The ionization chamber used for isodose measurements should?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Be small (sensitive volume, less than 15 mm long and inside diameter of 5 mm or less)
II.
Be energy dependent
III.
Be energy independent
IV.
Be as big as possible to cover the beam
36.
When using a wedge pair technique:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
The high-dose region (hot spot) is moved to the thick end of the wedges (heel).
II.
The high-dose region (hot spot) is moved to the thin end of the wedges (toe).
III.
The high-dose region (hot spot) decreases with field size and wedge angle.
IV.
The high-dose region (hot spot) increases with field size and wedge angle.
37.
Which of the following techniques can be used to obtain an acceptable uniform dose distribution?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Wedge pair
II.
Field in field
III.
Open field and wedged field combinations
IV.
Open field and block MLC field combinations
38.
The treatment planning process is based on?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Pathology
II.
Staging
III.
Diagnostic exams
IV.
Karnofsky score
39.
Which of the following organizations established or proposed a general dose specification system to be adopted universally?
A.
International Commission on Radiation Units and Measurements (ICRU)
B.
Nuclear Regulatory Commission (NRC)
C.
National Council on Radiation Protection and Measurements (NCRP)
D.
Atomic Energy Commission (AEC)
40.
The gross tumor volume (GTV):
A.
Is the tumor(s) if present and any other tissue with presumed tumor or microscopic disease
B.
Is the extent and location of the visible tumor only
C.
Compensates for internal physiological movements and variation in size, shape, and position of the CTV
D.
Includes the CTV and setup margin for patient movement and setup uncertainties
41.
Which of the following statement(s) are true?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Delineation of CTV assumes that there are no tumor cells outside this volume.
II.
Delineation of the GTV is possible if the tumor is visible, palpable, or demonstrable through imaging.
III.
The margin around CTV in any direction must be large enough to compensate for internal movements as well as patient motion and setup uncertainties.
IV.
GTV can be defined if the tumor has been surgically removed by outlining the tumor bed.
42.
Which of the following are correct about planning organ at risk (OAR)?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
It needs adequate protection.
II.
All organs at risk need the same margins.
III.
It may need margins to compensate for its movements, internal, as well as setup.
IV.
It is not of importance if abutting the PTV.
43.
Which of the following are correct about treatment volumes?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct
I.
It is larger than the planning target volume.
II.
It is a margin added to the target volume to allow for limitations of treatment technique.
III.
It depends on a particular treatment technique.
IV.
It is larger than the irradiated volume.
44.
The highest dose in the target area that covers a minimum of 2 cm2 is called:
A.
Hot spot
B.
Mean target dose
C.
Maximum target dose
D.
Modal target dose
45.
The reference point used to record target dose recommended by the ICRU:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Should represent dose throughout the PTV
II.
Should be selected where the dose can be accurately calculated
III.
Should not lie in the penumbra region
IV.
Should lie where steep dose gradient is
46.
The reference point used to record target dose recommended by the ICRU for parallel opposed, unequally weighted beams:
A.
Should be specified at the center of rotation in the principal plane
B.
Should be on the central axis midway between the beam entrances
C.
Should be specified on the central axis placed within the PTV
D.
Should be at the intersection of the central axes of the beams placed within the PTV
47.
Which of the following detectors is possibly traceable by NIST and/or ADCL?
A.
Ion chamber
B.
Radiochromic film
C.
Silicon detector
D.
TLD
3.2 Electron Beam Dose Distributions (Questions)
Quiz 1 (Level 2)
1.
Electron dose rate and isodose distribution depend on?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Electron energy
II.
Specific linear accelerator
III.
Secondary blocks
IV.
Field size
2.
The PDD for electron beams is uniform within the first few cm in tissue followed by a rapid falloff of dose. The depth at which this rapid falloff of dose is located depends on?
A.
Electron cutout
B.
Electron field size
C.
Electron cone
D.
Electron energy
3.
What electron energy in MeV should be selected if a tumor is located at 4 cm depth?
A.
6 MeV electron energy
B.
9 MeV electron energy
C.
12 MeV electron energy
D.
16 MeV electron energy
4.
The most clinically useful energy range for electrons is?
A.
12–24 MeV
B.
6–12 MeV
C.
6–20 MeV
D.
16–20 MeV
5.
Electron treatment can be used for all of the following except?
A.
Boost dose to nodes
B.
Skin and lip lesions
C.
Chest wall/breast irradiation
D.
Prostate irradiation
6.
Electrons interact with atoms through?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Inelastic collisions with atomic electrons
II.
Inelastic collisions with nuclei
III.
Elastic collisions with atomic electrons
IV.
Elastic collisions with nuclei
7.
The rate of electron energy loss depends primarily on:
A.
Electron density of the medium
B.
Type of cutout used
C.
Electron energy
D.
Type of collision
8.
The rate of energy loss per gram per cm squared (stopping power) is greater for?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
High atomic number materials
II.
Low atomic number materials
III.
High-Z materials
IV.
Low-Z materials
9.
The energy loss rate of electrons per cm in water is roughly about?
A.
3 MeV/cm of water
B.
2 MeV/cm of water
C.
1 MeV/cm of water
D.
2 KeV/cm of water
10.
For bremsstrahlung photon creation, the rate of energy loss in electron beam per cm is proportional to?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Electron energy
II.
Electron mass
III.
Square of the atomic number (Z 2)
IV.
Rest mass of an electron (0.511 MeV)
11.
The electron scattering power varies?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Inversely as the electron mass
II.
Approximately as the square of the atomic number (Z 2)
III.
Approximately as the square of the kinetic energy
IV.
Inversely as the square of the kinetic energy
12.
The practical electron range is defined as?
A.
The depth of the point where the tangent to the descending linear portion of the curve intersects the extrapolated background
B.
The depth at which the dose is 50 % of the maximum dose
C.
A point in space that is the same distance from the source for all gantry angles
D.
The thickness of the material that reduces the intensity of the beam to half (50 %) its original value
13.
As electron beam energy increases:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Dose increases
II.
Surface penumbra decreases
III.
Penumbra at depth increases
IV.
Surface penumbra increases
14.
What will be the correct energy if a physician asks the dosimetrist that he/she would like to prescribe an electron treatment at a depth of 3 cm using 90 % depth dose?
A.
6 MeV
B.
9 MeV
C.
12 MeV
D.
16 MeV
15.
Which of the following energies generates the highest surface dose or less skin sparing?
A.
6 MeV
B.
9 MeV
C.
12 MeV
D.
16 MeV
16.
Superficial tumors are best treated with:
A.
Photon treatments
B.
Electron treatments
C.
Proton treatments
D.
CyberKnife treatments
17.
The most useful treatment depth or therapeutic range of electrons is given by:
A.
50 % depth dose
B.
90 % depth dose
C.
100 % depth dose
D.
25 % depth dose
18.
If the treatment depth on an electron is in doubt, the dosimetrist should:
A.
Use a bigger cutout.
B.
Use a bigger cone size.
C.
Use higher electron energy.
D.
Treatment depth is not important.
19.
Which of the following statements are true?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
The skin-sparing effect with clinical electron beams is only modest or nonexistent.
II.
Percent surface dose for electrons increases with energy.
III.
At lower energies, the electrons are scattered more easily and through larger angles.
IV.
The ratio of surface dose to maximum dose is less for the lower-energy electrons than for the higher-energy electrons.
20.
Uniformity or flatness of the electron beam is usually specified:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
In a plane perpendicular to the beam axis
II.
Horizontal to the beam axis
III.
At the depth of the 95 % isodose beyond the depth of dose maximum
IV.
At Dmax
21.
Which of the following statements are true?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
The symmetry of electron beam is the comparison of a dose profile on one side of the central axis to that on the other.
II.
AAPM recommends that the cross-beam profile in the reference plane should not differ more than 2 % at any pair of points located symmetrically on opposite sides of the central axis.
III.
AAPM recommends that the variation in dose relative to the dose at the central axis should not exceed ±5 % over an area confined within lines 2 cm inside the geometric edge of fields equal to or larger than 10 × 10 cm.
IV.
Scattering foils widen the electron beam as well as give a uniform dose distribution across the treatment field.
22.
Acceptable field flatness and symmetry on an electron beam can be obtained:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Using the MLC
II.
Using proper design of beam scatterers
III.
Using cones close to the skin
IV.
Using proper beam-defining collimators
23.
An electron beam emanates from:
A.
The physical source
B.
A virtual point
C.
The target
D.
The cutout
24.
The tail of the electron depth-dose curve at the point where it becomes straight is due to:
A.
Photoelectric effect interactions of electrons with the collimator system
B.
Bremsstrahlung interactions of electrons with the collimator system
C.
Bremsstrahlung interactions of electrons with the target
D.
Bremsstrahlung interactions of electrons with the patient
25.
Which of the following electron fields has the highest PDD?
A.
I only.
B.
II only.
C.
III only.
D.
IV only.
E.
All have the same PDD.
I.
10 × 10 cm
II.
10 × 15 cm
III.
10 × 20 cm
IV.
20 × 20 cm
26.
In an electron treatment, energy should be selected based on:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Depth of target volume
II.
Minimum target dose required
III.
Clinically acceptable dose to critical organs
IV.
Field size used
27.
Electron beam obliquity tends to:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Increase side scatter at Dmax
II.
Decrease the depth of penetration
III.
Shift Dmax toward the surface
IV.
Shift Dmax away from the surface
28.
For a large and uniform slab, the dose distribution for an electron beam beyond an inhomogeneity can be corrected by using:
A.
TAR method
B.
Effective SSD method
C.
Isodose shift method
D.
Coefficient equivalent thickness (CET) method
29.
Bolus is often used in electron beam therapy to:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Flatten out an irregular surface
II.
Reduce the penetration of the electrons in parts of the field
III.
Increase the surface dose
IV.
Increase the depth-dose
30.
Some bolus materials used for radiation treatment are:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Paraffin wax
II.
Polystyrene
III.
Lucite
IV.
Superflab
31.
A plate of low atomic number material used on the patient’s skin to reduce the energy of an electron beam is known as?
A.
Accelerators
B.
Decelerators
C.
Compensators
D.
Wedges
32.
Bolus should conform to the patient’s surface as much as possible. Large air gaps between the absorber and the surface would result in:
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Reduction in dose
II.
Increase in dose
III.
Scattering of electrons outside the field
IV.
Scattering of electrons inside the field
33.
When an electron field is abutted at the surface with a photon field?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Hot spot develops on the side of the electron field.
II.
Hot spot develops on the side of the photon field.
III.
Cold spot develops on the side of the photon field.
IV.
Cold spot develops on the side of the electron field.
34.
Field shaping can be accomplished in electron beam therapy by using?
A.
MLC
B.
Cones
C.
Cutout
D.
Wedges
35.
Adequate cutout transmission for an electron beam treatment is?
A.
≤5 % transmission
B.
>5 % transmission
C.
±10 % of the given dose
D.
±15 % of the given dose
36.
What is the required thickness of a lead cutout for electron energies less than 10 MeV in order to keep an acceptable transmission or reduce the dose to an acceptable value to critical structures?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
5 mm thickness of lead
II.
5 cm thickness of lead
III.
6 mm thickness of Cerrobend
IV.
5 cm thickness of lead
37.
The required thickness of Cerrobend is approximately?
A.
50 % greater than that of pure lead
B.
30 % greater than that of pure lead
C.
20 % greater than that of pure lead
D.
Equal to that of pure lead
38.
As a rule of thumb, the minimum thickness of lead required for blocking of electrons in mm is given by?
A.
Electron energy in MeV/4
B.
Electron energy in MeV/2
C.
Electron energy in MeV × 2
D.
Electron energy in MeV + 4
39.
Which of the following treatments often require internal shielding?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Lip treatments
II.
Buccal mucosa
III.
Eyelid lesions
IV.
Stoma lesions
40.
Which of the following cases have the most substantial change of dose due to electron backscatter?
A.
Lung tissue interface
B.
Shielding shape
C.
Tissue-lead interface
D.
Bone tissue interface
41.
To dissipate the effect of electron backscatter (a bremsstrahlung) on an internal lead, shield is recommended to?
A.
I, II, and III.
B.
I and III only.
C.
II and IV only.
D.
IV only.
E.
All are correct.
I.
Use a low atomic number absorber between the lead shield and the preceding tissue surface.
II.
Use aluminum sheath around any lead used for internal shielding.
III.
Use dental acrylic around any oral shielding.
IV.
Use an internal cutout of size bigger than 3 cm always.
42.
The physician wants to treat the lower lip which measures 2 cm thick using a 9 MeV electron beam. What is the thickness of lead required in order to protect the structures beyond the lips?
A.
2 mm
B.
2.5 cm
C.
2.5 mm
D.
4.5 cm
43.
A superficial tumor along a curved surface such as the chest wall or ribs is better treated with?
A.
Multiple abutting electron fields
B.
Electron arc therapy
C.
Rapid arc photon therapy
D.
Pseudo-arc technique
44.
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What energies are most used for total skin irradiation?
A.
9–12 MeV.
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