MDCB LATEST 2026 MAIN FINALS ALL QUESTIONS AND
ANSWERS MARKED A+
✔✔Tissue Compensators - ✔✔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 - ✔✔Physical Penumbra of
MLCs are wider than both jaws and cerrobend blocks
✔✔CNS Planning: Cranial Field Orientation (Formula, given Spine Field Settings) -
✔✔θ(collimator) = arc tan (½ L₁/SSD)
θ(couch) = arc tan (½ L₂/SSD)
where
SSD is with regard to Spine Field
L₁ is length of PA Spine Field
L₂ is length of Cranial Field (sup to inf)
✔✔TAR, TPR, TMR, SAR - ✔✔TAR = tissue air ratio = D(d)/D(air)
TPR = tissue phantom ratio = D(d)/D(ref)
TMR = tissue maximum ratio = D(d)/D(dmax)
SAR = scatter air ratio = TAR(d,r) - TAR(d,0) where r is field size
✔✔(4) Personnel Monitoring and how they work - ✔✔1. film badges: consists of film
between metal filters. metal filters are used to determine the quality of the radiation
absorbed, and the film is read using optical density proportional to the dose received.
2. TLD's: thermoluminscent dosimeter; uses lithium fluoride (LiF) crystal that stores
energy by trapping electrons, which can be read by heating the crystals to emit light
photons.
3. OSL's: optically stimulating luminescence; uses aluminum oxide with carbon that
stores energy in the crystal, measured by shining a green laser at crystal and measure
intensity of blue light.
4. pocket ionization chambers: used by charging the device, and looking through the
eyepiece to note amount of charge lost upon irradiation.
✔✔Pinnacle Acronyms: ODM, SVD, TPB - ✔✔ODM: opening density matrix - use for
very small fields or machines with MLCs <5mm width.
TPB: Todd's/Tradiational Pencil Beam - a method of beam optimization
SVD: single value decomposition - a method of beam optimization similar but superior
to TPB
, ✔✔V vs eV - ✔✔V: polyenergetic energy spectrum
eV: monoenergetic energy
✔✔Components of a Linac - ✔✔magnetron: microwave generator
klystron: microwave amplifier
modulator: modulates high frequency pulses
circulator: prevents reflected microwaves from reaching the magnetron
power supply: powers modulator (direct current)
waveguide: conducts microwaves to electron gun
electron gun: source of electrons
accelerator tube: accelerates electrons to treatment head using high voltages
bending magnet: creates homogeneous energy electrons
target: produce x-rays (bremstrahlung)
flattening filter: flattens x-ray beams for uniformity
scattering foil: scatters electron beams for uniformity
ion chamber: verifies beam output and flatness
collimation/jaws: shapes beam
✔✔Retrospective vs Prospective Planning - ✔✔Retrospective: forward planning
Prospective: inverse/IMRT planning
✔✔DICOM RT Objects (5) - ✔✔- RT Image: DRRs, portals, CT/sim
- RT Plan (RTP): geometric and dosimetric data - linked to structure
- RT Structure set (RTSS): anatomy with respect to isocenters and markers
- RT Dose: dose distribution, DVH
- RT Tx Record: data from treatment sessions
✔✔Types of Simulators (3) - ✔✔1. conventional/fluoro: isocentrically-mounted x-ray
tube, with gantry, imager, xray generator, and couch
2. conventional with CT acquisition: CBCT, 3D plan verifications
3. CT simulator: CT machine and laser system with virtual simulator application, 4D
studies
✔✔Brachytherapy Radiation Safety for Permanent Implants - ✔✔- high activity patients
(30mCi or greater) must be hospitalized until decay levels decrease to <30mCi or 10
mR/hr.
- dose rate outside patient room needs to be ≤2 mrem/hr.
- expensive, requires trained staff to care for patient, and a shielded room
✔✔Methods of Brachytherapy Localization (2) - ✔✔- orthogonal imaging: 90° difference
between two port films
- stereo-shift method: two ports of same view but shifted a certain distance between
exposures on two different films. this is to view the number of seeds on one film and
then the other
ANSWERS MARKED A+
✔✔Tissue Compensators - ✔✔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 - ✔✔Physical Penumbra of
MLCs are wider than both jaws and cerrobend blocks
✔✔CNS Planning: Cranial Field Orientation (Formula, given Spine Field Settings) -
✔✔θ(collimator) = arc tan (½ L₁/SSD)
θ(couch) = arc tan (½ L₂/SSD)
where
SSD is with regard to Spine Field
L₁ is length of PA Spine Field
L₂ is length of Cranial Field (sup to inf)
✔✔TAR, TPR, TMR, SAR - ✔✔TAR = tissue air ratio = D(d)/D(air)
TPR = tissue phantom ratio = D(d)/D(ref)
TMR = tissue maximum ratio = D(d)/D(dmax)
SAR = scatter air ratio = TAR(d,r) - TAR(d,0) where r is field size
✔✔(4) Personnel Monitoring and how they work - ✔✔1. film badges: consists of film
between metal filters. metal filters are used to determine the quality of the radiation
absorbed, and the film is read using optical density proportional to the dose received.
2. TLD's: thermoluminscent dosimeter; uses lithium fluoride (LiF) crystal that stores
energy by trapping electrons, which can be read by heating the crystals to emit light
photons.
3. OSL's: optically stimulating luminescence; uses aluminum oxide with carbon that
stores energy in the crystal, measured by shining a green laser at crystal and measure
intensity of blue light.
4. pocket ionization chambers: used by charging the device, and looking through the
eyepiece to note amount of charge lost upon irradiation.
✔✔Pinnacle Acronyms: ODM, SVD, TPB - ✔✔ODM: opening density matrix - use for
very small fields or machines with MLCs <5mm width.
TPB: Todd's/Tradiational Pencil Beam - a method of beam optimization
SVD: single value decomposition - a method of beam optimization similar but superior
to TPB
, ✔✔V vs eV - ✔✔V: polyenergetic energy spectrum
eV: monoenergetic energy
✔✔Components of a Linac - ✔✔magnetron: microwave generator
klystron: microwave amplifier
modulator: modulates high frequency pulses
circulator: prevents reflected microwaves from reaching the magnetron
power supply: powers modulator (direct current)
waveguide: conducts microwaves to electron gun
electron gun: source of electrons
accelerator tube: accelerates electrons to treatment head using high voltages
bending magnet: creates homogeneous energy electrons
target: produce x-rays (bremstrahlung)
flattening filter: flattens x-ray beams for uniformity
scattering foil: scatters electron beams for uniformity
ion chamber: verifies beam output and flatness
collimation/jaws: shapes beam
✔✔Retrospective vs Prospective Planning - ✔✔Retrospective: forward planning
Prospective: inverse/IMRT planning
✔✔DICOM RT Objects (5) - ✔✔- RT Image: DRRs, portals, CT/sim
- RT Plan (RTP): geometric and dosimetric data - linked to structure
- RT Structure set (RTSS): anatomy with respect to isocenters and markers
- RT Dose: dose distribution, DVH
- RT Tx Record: data from treatment sessions
✔✔Types of Simulators (3) - ✔✔1. conventional/fluoro: isocentrically-mounted x-ray
tube, with gantry, imager, xray generator, and couch
2. conventional with CT acquisition: CBCT, 3D plan verifications
3. CT simulator: CT machine and laser system with virtual simulator application, 4D
studies
✔✔Brachytherapy Radiation Safety for Permanent Implants - ✔✔- high activity patients
(30mCi or greater) must be hospitalized until decay levels decrease to <30mCi or 10
mR/hr.
- dose rate outside patient room needs to be ≤2 mrem/hr.
- expensive, requires trained staff to care for patient, and a shielded room
✔✔Methods of Brachytherapy Localization (2) - ✔✔- orthogonal imaging: 90° difference
between two port films
- stereo-shift method: two ports of same view but shifted a certain distance between
exposures on two different films. this is to view the number of seeds on one film and
then the other
