MEDICAL DOSIMETRY EVALUATION 2026 TEST
QUESTIONS AND ANSWERS SURE A+
✔✔presence of bone in the beam path decreases the dose behind the bone per
centimeter of bone for a 10 MV X-ray beam by about_____ - ✔✔2%
✔✔presence of bone in the beam path decreases the dose behind the bone for a 60
cobalt beam by about______ - ✔✔3.5%
✔✔in the iso dose shift method used for correcting for inhomogeneity in a patient, for a
point line beyond the inhomogeneity, the shift______ - ✔✔of the isodose chart is
towards the skin for bone
of isodose chart is away from the skin for long
✔✔some methods available for correcting for surface obliquity are: - ✔✔- isodose shift
method
- effective SSD method
- TAR method
✔✔the Isodose shift method - ✔✔is the easiest of all methods used for surface obliquity
correction and can be used to correct a complete isodose curve
,✔✔Isodose shift factor_____ - ✔✔decreases with increasing beam energy and shifts
the isotopes curve toward the surface in case of tissue excess
✔✔film can be used for measuring______ - ✔✔The electron beam depth dose profile
and its range parameters
✔✔for measuring the range parameters of an electron beam what is essential? -
✔✔lateral scatter equilibrium
✔✔for electron beams, output or PDD becomes field size dependent when_____ -
✔✔There is no lateral scatter equilibrium
✔✔The clinical electron beam incident on a patient______ - ✔✔exhibits a spectrum
has a range parameter, R50, that is of relevance in dosimetry
✔✔a clinical electron beam exhibits a narrow spectrum, which is characterized by a
maximum energy, most probable energy, mean energy, and a spectral width. - ✔✔The
most probable energy is related to the practical range of the electron beam
the mean energy is related to clinical dosimetry
✔✔The interaction of a pencil beam of electrons with the accelerator components (such
as a scattering foil monitor chamber collimators etc) and the patient result in_____ -
✔✔lateral spreading of the beam due to scattering
production of low energy electrons increasing the width of the spectrum
production of bremsstrahlung X-rays
✔✔The range of a 10 MeV electron beam in water is about______ - ✔✔5 cm
✔✔what is the rough energy of a 10 MeV electron beam incident on water phantom at a
depth of 2 cm? - ✔✔6
✔✔for a clinical electron beam: - ✔✔The skin dose increases with increasing electron
energy
R50,D is related to mean energy of the beam
The reference depth for beam calibration per the AAPM protocol TG51 is 0.6 R50,D -
0.1 cm
✔✔a clinical electron beam is contaminated with_____ - ✔✔bremsstrahlung photons
,✔✔beyond the range, a clinical electron beam______ - ✔✔deposits no energy and has
a bremsstrahlung tail of a few percent
✔✔The electron depth dose measurements in water must be carried out with_____ -
✔✔an ionization chamber or silicon diode
✔✔for an electron beam, lateral scatter equilibrium exist when the field size is_____ -
✔✔of the order of the electron energy
✔✔for a 10 MeV couldn't call electron beam, incident on the patient, the required field
size for lateral scatter equilibrium is about______ - ✔✔10 cm x 10 cm
✔✔electron beams of different field sizes are produced using______ - ✔✔different
applicator cone attachments to the linac head
or different cutouts inside cones
✔✔according to the AAPM TG51 dosimetry protocol, the reference depth for electron
beam calibration in cm is_____ - ✔✔0.6 R50,D - 0.1
✔✔The reference depth for monitor unit calculations in electron beam therapy is_____ -
✔✔D-Max
✔✔The pencil electron beam coming out of a wave guide is spread into larger field
sizes, in a clinical accelerator using: - ✔✔scattering foils
electromagnetic scanning
✔✔the virtual source of a clinical electron being always lies at_____ - ✔✔an
experimentally determined distance
✔✔an electron beam therapy, the dose prescription point is generally______ - ✔✔90%
Isodose depth
✔✔an electron beam is incident obliquely on a patient. compared to normal incidence
situation,______ - ✔✔skin dose increases
therapeutic depth shifts towards the surface
✔✔when cutouts are used to shape electron fields, cut out factors must be determined
for each cut out for accurate dosimetry. however the output variation is not very
, significant if the______ - ✔✔open area or cut out area is still large enough for lateral
electronic equilibrium
✔✔in electron beam therapy sometimes internal shielding is used to reduce the
transmitted dose to normal tissues beyond the treatment volume. if lead or some high z
material is used as an internal shield, one must take care of______ - ✔✔backscatter of
electrons that may overdose normal tissues
✔✔electron back scatter from internal shielding: - ✔✔increases with Z
decreases with increase in energy
is absorbed in low Z material lining so they do not overdose normal tissues
✔✔The depth of maximum absorbed dose, D-Max, along the beam CAX is_____ -
✔✔The reference depth for treatment time or monitor unit calculation
✔✔PDD is normalized at: - ✔✔D-Max for SSD technique
Target center for isocentric techniques
✔✔PDD increases with - ✔✔field size
✔✔PDD is normalized to 100% at_____ - ✔✔Dmax
✔✔The field size dependence of PDD occurs due to: - ✔✔increased electron scatter
that influences the dose on skin and build up depths
increased phantom scatter
✔✔surface dose increases with - ✔✔field size
✔✔surface dose for clean clinical photon beams is______ - ✔✔about 10% to 50%
✔✔electron contamination: - ✔✔-increases the surface dose
-increases dose in buildup region
- decreases for increasing diaphragm skin distance
- increases with field size
✔✔dose build up in the build-up region is - ✔✔not linear and very steep in the initial
portion of buildup (leads to skin-sparing)
✔✔from isodose curves measured, eg in the principal plane, one can determine: -
✔✔CAX depth dose values
QUESTIONS AND ANSWERS SURE A+
✔✔presence of bone in the beam path decreases the dose behind the bone per
centimeter of bone for a 10 MV X-ray beam by about_____ - ✔✔2%
✔✔presence of bone in the beam path decreases the dose behind the bone for a 60
cobalt beam by about______ - ✔✔3.5%
✔✔in the iso dose shift method used for correcting for inhomogeneity in a patient, for a
point line beyond the inhomogeneity, the shift______ - ✔✔of the isodose chart is
towards the skin for bone
of isodose chart is away from the skin for long
✔✔some methods available for correcting for surface obliquity are: - ✔✔- isodose shift
method
- effective SSD method
- TAR method
✔✔the Isodose shift method - ✔✔is the easiest of all methods used for surface obliquity
correction and can be used to correct a complete isodose curve
,✔✔Isodose shift factor_____ - ✔✔decreases with increasing beam energy and shifts
the isotopes curve toward the surface in case of tissue excess
✔✔film can be used for measuring______ - ✔✔The electron beam depth dose profile
and its range parameters
✔✔for measuring the range parameters of an electron beam what is essential? -
✔✔lateral scatter equilibrium
✔✔for electron beams, output or PDD becomes field size dependent when_____ -
✔✔There is no lateral scatter equilibrium
✔✔The clinical electron beam incident on a patient______ - ✔✔exhibits a spectrum
has a range parameter, R50, that is of relevance in dosimetry
✔✔a clinical electron beam exhibits a narrow spectrum, which is characterized by a
maximum energy, most probable energy, mean energy, and a spectral width. - ✔✔The
most probable energy is related to the practical range of the electron beam
the mean energy is related to clinical dosimetry
✔✔The interaction of a pencil beam of electrons with the accelerator components (such
as a scattering foil monitor chamber collimators etc) and the patient result in_____ -
✔✔lateral spreading of the beam due to scattering
production of low energy electrons increasing the width of the spectrum
production of bremsstrahlung X-rays
✔✔The range of a 10 MeV electron beam in water is about______ - ✔✔5 cm
✔✔what is the rough energy of a 10 MeV electron beam incident on water phantom at a
depth of 2 cm? - ✔✔6
✔✔for a clinical electron beam: - ✔✔The skin dose increases with increasing electron
energy
R50,D is related to mean energy of the beam
The reference depth for beam calibration per the AAPM protocol TG51 is 0.6 R50,D -
0.1 cm
✔✔a clinical electron beam is contaminated with_____ - ✔✔bremsstrahlung photons
,✔✔beyond the range, a clinical electron beam______ - ✔✔deposits no energy and has
a bremsstrahlung tail of a few percent
✔✔The electron depth dose measurements in water must be carried out with_____ -
✔✔an ionization chamber or silicon diode
✔✔for an electron beam, lateral scatter equilibrium exist when the field size is_____ -
✔✔of the order of the electron energy
✔✔for a 10 MeV couldn't call electron beam, incident on the patient, the required field
size for lateral scatter equilibrium is about______ - ✔✔10 cm x 10 cm
✔✔electron beams of different field sizes are produced using______ - ✔✔different
applicator cone attachments to the linac head
or different cutouts inside cones
✔✔according to the AAPM TG51 dosimetry protocol, the reference depth for electron
beam calibration in cm is_____ - ✔✔0.6 R50,D - 0.1
✔✔The reference depth for monitor unit calculations in electron beam therapy is_____ -
✔✔D-Max
✔✔The pencil electron beam coming out of a wave guide is spread into larger field
sizes, in a clinical accelerator using: - ✔✔scattering foils
electromagnetic scanning
✔✔the virtual source of a clinical electron being always lies at_____ - ✔✔an
experimentally determined distance
✔✔an electron beam therapy, the dose prescription point is generally______ - ✔✔90%
Isodose depth
✔✔an electron beam is incident obliquely on a patient. compared to normal incidence
situation,______ - ✔✔skin dose increases
therapeutic depth shifts towards the surface
✔✔when cutouts are used to shape electron fields, cut out factors must be determined
for each cut out for accurate dosimetry. however the output variation is not very
, significant if the______ - ✔✔open area or cut out area is still large enough for lateral
electronic equilibrium
✔✔in electron beam therapy sometimes internal shielding is used to reduce the
transmitted dose to normal tissues beyond the treatment volume. if lead or some high z
material is used as an internal shield, one must take care of______ - ✔✔backscatter of
electrons that may overdose normal tissues
✔✔electron back scatter from internal shielding: - ✔✔increases with Z
decreases with increase in energy
is absorbed in low Z material lining so they do not overdose normal tissues
✔✔The depth of maximum absorbed dose, D-Max, along the beam CAX is_____ -
✔✔The reference depth for treatment time or monitor unit calculation
✔✔PDD is normalized at: - ✔✔D-Max for SSD technique
Target center for isocentric techniques
✔✔PDD increases with - ✔✔field size
✔✔PDD is normalized to 100% at_____ - ✔✔Dmax
✔✔The field size dependence of PDD occurs due to: - ✔✔increased electron scatter
that influences the dose on skin and build up depths
increased phantom scatter
✔✔surface dose increases with - ✔✔field size
✔✔surface dose for clean clinical photon beams is______ - ✔✔about 10% to 50%
✔✔electron contamination: - ✔✔-increases the surface dose
-increases dose in buildup region
- decreases for increasing diaphragm skin distance
- increases with field size
✔✔dose build up in the build-up region is - ✔✔not linear and very steep in the initial
portion of buildup (leads to skin-sparing)
✔✔from isodose curves measured, eg in the principal plane, one can determine: -
✔✔CAX depth dose values
