MDCB Concepts Exam Actual Questions
and Answers 2026
Hounsfield Units -
correct answer ✅A measure of the beam attenuation capability of
a specific structure. Also called pixel values, density numbers or CT
numbers.
HU = 1000 · [µ(tissue) - µ(water)] ÷ µ(water)
bone ∼ 1000
tissue ∼ 0
air ∼ -1000
Factors in Calculating Monitor Units -
correct answer ✅output factor
scatter factors (Sc, Sp, Scp)
inverse square factor
depth dose factor (PDD, TMR)
off-axis factor
transmission factor (tray, wedge)
MU = Rx Dose ÷ Final Output
,MDCB Concepts Exam Actual Questions
and Answers 2026
Using Inverse Square Law -
correct answer ✅Relationship between intensity and the distance
from the source: d₁² x I₁ = d₂² x I₂
ex: Output at 1cm = 160 cGy
Output at 100cm = ?
(1cm)²(160cGy) = (100cm)²I₂
I₂ = 0.016cGy
SAD Set Up: Finding Dose at 2nd point of calculation using TMRs -
correct answer ✅D1 = D2 x (TMR1/TMR2) x (SAD2/SAD1)²
Definition of a Wedge Angle -
correct answer ✅the angle between an isodose curve at specified
depth and a line perpendicular to the CAX at the same specified
depth
Dose Computation Algorithms -
correct answer ✅Correction-Based: based on measured data in a
phantom and applied correction factors (attenuation, scatter, f/s,
shape, geometry, inverse square law, etc)
,MDCB Concepts Exam Actual Questions
and Answers 2026
Model-Based: based on physical model simluating actual transport
of scattered photons and electrons: ie. Convolution-Superposition
and Monte Carlo....
Convolution-Superposition: simulates primary photon track and
calculates separately scatter photons/electrons
Monte Carlo: simulates transport of millions of photons and
particles through matter using fundamental laws of physics
(requiring long computation time and power)
Proton Radiation Therapy -
correct answer ✅- High LET means minimal dose dumping along
path until the velocity decreases enough to dump the rest of the
dose in a small area (narrow bragg peak). Brag peak can be spread
out (SOBP) across target volume by adjusting beam energy.
- protons increase cell kill over xrays and has superior dose
distribution and critical structure sparing.
- protons produced in cyclotron.
- stopping power is inversely proportional to velocity squared.
TBI Treatment -
correct answer ✅- used to condition the body for bone marrow
transplantations for diseases like leukemia.
, MDCB Concepts Exam Actual Questions
and Answers 2026
- use photons to achieve ±10% uniformity of dose using spoiler and
TBI filters, prescribed to midplane at the umbilicus.
- 6 fractions BID is per usual
- pneumonitis (lungs) are the dose limiting factor
- dose validations are made using diodes, TLDs
Tissue Compensators -
correct answer ✅sometimes surface irregularities gives rise to
unacceptable non-uniformity in target or excessive dose in critical
structures, requiring the use of tissue compensators like:
- wedges
- multiple fields
- bolus: to even irregular patient contours
- compensators: preserves skin sparing effect whereas bolus does
not
- blocked for some fractions
Physical Penumbra of MLCs vs Cerrobend vs Jaws -
correct answer ✅Physical Penumbra of MLCs are wider than both
jaws and cerrobend blocks
and Answers 2026
Hounsfield Units -
correct answer ✅A measure of the beam attenuation capability of
a specific structure. Also called pixel values, density numbers or CT
numbers.
HU = 1000 · [µ(tissue) - µ(water)] ÷ µ(water)
bone ∼ 1000
tissue ∼ 0
air ∼ -1000
Factors in Calculating Monitor Units -
correct answer ✅output factor
scatter factors (Sc, Sp, Scp)
inverse square factor
depth dose factor (PDD, TMR)
off-axis factor
transmission factor (tray, wedge)
MU = Rx Dose ÷ Final Output
,MDCB Concepts Exam Actual Questions
and Answers 2026
Using Inverse Square Law -
correct answer ✅Relationship between intensity and the distance
from the source: d₁² x I₁ = d₂² x I₂
ex: Output at 1cm = 160 cGy
Output at 100cm = ?
(1cm)²(160cGy) = (100cm)²I₂
I₂ = 0.016cGy
SAD Set Up: Finding Dose at 2nd point of calculation using TMRs -
correct answer ✅D1 = D2 x (TMR1/TMR2) x (SAD2/SAD1)²
Definition of a Wedge Angle -
correct answer ✅the angle between an isodose curve at specified
depth and a line perpendicular to the CAX at the same specified
depth
Dose Computation Algorithms -
correct answer ✅Correction-Based: based on measured data in a
phantom and applied correction factors (attenuation, scatter, f/s,
shape, geometry, inverse square law, etc)
,MDCB Concepts Exam Actual Questions
and Answers 2026
Model-Based: based on physical model simluating actual transport
of scattered photons and electrons: ie. Convolution-Superposition
and Monte Carlo....
Convolution-Superposition: simulates primary photon track and
calculates separately scatter photons/electrons
Monte Carlo: simulates transport of millions of photons and
particles through matter using fundamental laws of physics
(requiring long computation time and power)
Proton Radiation Therapy -
correct answer ✅- High LET means minimal dose dumping along
path until the velocity decreases enough to dump the rest of the
dose in a small area (narrow bragg peak). Brag peak can be spread
out (SOBP) across target volume by adjusting beam energy.
- protons increase cell kill over xrays and has superior dose
distribution and critical structure sparing.
- protons produced in cyclotron.
- stopping power is inversely proportional to velocity squared.
TBI Treatment -
correct answer ✅- used to condition the body for bone marrow
transplantations for diseases like leukemia.
, MDCB Concepts Exam Actual Questions
and Answers 2026
- use photons to achieve ±10% uniformity of dose using spoiler and
TBI filters, prescribed to midplane at the umbilicus.
- 6 fractions BID is per usual
- pneumonitis (lungs) are the dose limiting factor
- dose validations are made using diodes, TLDs
Tissue Compensators -
correct answer ✅sometimes surface irregularities gives rise to
unacceptable non-uniformity in target or excessive dose in critical
structures, requiring the use of tissue compensators like:
- wedges
- multiple fields
- bolus: to even irregular patient contours
- compensators: preserves skin sparing effect whereas bolus does
not
- blocked for some fractions
Physical Penumbra of MLCs vs Cerrobend vs Jaws -
correct answer ✅Physical Penumbra of MLCs are wider than both
jaws and cerrobend blocks
