MDCB UPDATED ACTUAL FINAL PAPER QUESTIONS
AND ANSWERS MARKED A+
✔✔IGRT Image Guidance Technologies
1. Port/Radiograph
2. In-Room CT Scanner
3. kV cone beam CT
4. MV cone beam CT
5. Helical Tomotherapy
6. Ultrasound - ✔✔1. Port/Radiograph = kV images with mounted xray tube on gantry
with opposing flat panel detector; MV images with EPID (electronic portal imaging
device) with opposing flat panel detector
2. in-room CT = conventional CT on rails, share couch with the treatment machine, but
separate machine (rotate the couch to use either CT on rails, or treatment machine)
3. kV cone beam CT = radiography, fluoroscopy, and CBCT, which acquires planar
projection images as the gantry rotates, reoncstructing 3D patient using filtered back-
projection algorithm
4. MV cone beam CT = use of traditional EPID and flat panel detector, where the source
is the treatment machine gantry itself. works as well as kV CBCT but with less contrast.
5. helical tomotherapy = integration of CT imaging and treatment in the same device
6. ultrasound = poor image quality and requires skilled technicians to create 3D
reconstructions of 2D images (requires huge margins)
✔✔structural shielding design for controlled and non-controlled areas - ✔✔controlled
limits: 0.1 rem/wk or 5 rem/yr
non-controlled limits: 0.01 rem/wk or 0.5 rem/yr
rooms require protection from primary radiation, scatter, and leaked radiation. primary
and secondary barriers are determined by workload W, use factor U, occupancy factor
T, and distance.
U = 1 for floors, 1/4 for walls, 1/2-1/4 for ceilings
✔✔medical event - ✔✔- total dose or dosage exceeds 20% of prescription
- dose for single fraction exceeds 50% of prescription dose/fx
✔✔written directive - ✔✔dated and signed by authorized user
patient name
source, dosage, route of adminstration, total dose, tx site, dose/fx, dose rate, number of
fx's
✔✔CT Numbers and CT Imaging - ✔✔CT Numbers: bear a linear relationship to
attenuation coefficients. depend on electron density (and atomic number for xrays). the
correlation was established in scanning phantoms of known density in the range
including lung, muscle, and bone densities.
CT Imaging: computed tomography uses synchronously rotating xray generators
opposing radiation detectors. the distribution of attenuation coefficients can be
, determined if a sufficient number of transmission measurements are acquired and CT
image can be reconstructed.
✔✔patient positioning guidelines - ✔✔- isocentric treatment reduces patient movement
between fields
- isocenter position established using CT with AP,RLAT radiographs to define target
volume
- do not use thick pads or matresses
- noting and reproducing SSD at isocenter
- skin marks should not be sole localization method, because of skin sag and rotation.
- field sizes are to be defined at the isocenter
✔✔autoradiography of encapsulated brachytherapy source - ✔✔a test for gross
nonuniformity of the radionuclide within a source capsule
✔✔LET: characteristics low to high, cell survival curve, dependencies (E, OER, RBE) -
✔✔LET = linear energy transfer in keV/µm, proportional to Q²/V²
low LET: x and gamma radiation, no mass or charge. photon interactions produce
electrons that may deliver dose far off track
medium LET: neutrons, no charge, still highly ionizing because of mass
high LET: alpha particles, have mass and charge, so are very ionizing and produce
many ionizations within a short distance
- cell survival ↓ with ↑ LET
- LET ↓ with ↑ E
- OER ↓ and RBE ↑ (with ↑ LET)
✔✔stopping power - ✔✔locally absorbed energy lost per unit path length.
- "restricted" does not include scatter (restricted < unrestricted)
- s↓ with ↑E, ↑velocity, ↑Z
✔✔scatter radiation characteristics (back and forward scatter) - ✔✔- low energy
photons have more backscatter. max backscatter is at 0.6-0.8mm Cu HVL.
- as photon energy increases, scatter moves more forward.
- dose to any point within a treatment field is due to contributions from both primary and
scatter radiation
- back scatter increases with ↑ in f/s (↑ collimator scatter) and is independent of SSD
✔✔interstitial brachytherapy planning "systems" (methods) - ✔✔Quimby System and
Paris System: uniform placement of needles in row, non-uniform dose distribution
Paterson Parker AKA Manchester System = needle placement defined per calculated
pattern giving nearly uniform dose (max variation ±10% prescription dose)
✔✔tandem and ovoid planning (points A and B) - ✔✔point A: where uterine vessels
cross the ureter -- the main limiting factor for radiation of uterine cervix. = 2cm sup from
os along tandem and 2cm lateral perpendicular to tandem.
AND ANSWERS MARKED A+
✔✔IGRT Image Guidance Technologies
1. Port/Radiograph
2. In-Room CT Scanner
3. kV cone beam CT
4. MV cone beam CT
5. Helical Tomotherapy
6. Ultrasound - ✔✔1. Port/Radiograph = kV images with mounted xray tube on gantry
with opposing flat panel detector; MV images with EPID (electronic portal imaging
device) with opposing flat panel detector
2. in-room CT = conventional CT on rails, share couch with the treatment machine, but
separate machine (rotate the couch to use either CT on rails, or treatment machine)
3. kV cone beam CT = radiography, fluoroscopy, and CBCT, which acquires planar
projection images as the gantry rotates, reoncstructing 3D patient using filtered back-
projection algorithm
4. MV cone beam CT = use of traditional EPID and flat panel detector, where the source
is the treatment machine gantry itself. works as well as kV CBCT but with less contrast.
5. helical tomotherapy = integration of CT imaging and treatment in the same device
6. ultrasound = poor image quality and requires skilled technicians to create 3D
reconstructions of 2D images (requires huge margins)
✔✔structural shielding design for controlled and non-controlled areas - ✔✔controlled
limits: 0.1 rem/wk or 5 rem/yr
non-controlled limits: 0.01 rem/wk or 0.5 rem/yr
rooms require protection from primary radiation, scatter, and leaked radiation. primary
and secondary barriers are determined by workload W, use factor U, occupancy factor
T, and distance.
U = 1 for floors, 1/4 for walls, 1/2-1/4 for ceilings
✔✔medical event - ✔✔- total dose or dosage exceeds 20% of prescription
- dose for single fraction exceeds 50% of prescription dose/fx
✔✔written directive - ✔✔dated and signed by authorized user
patient name
source, dosage, route of adminstration, total dose, tx site, dose/fx, dose rate, number of
fx's
✔✔CT Numbers and CT Imaging - ✔✔CT Numbers: bear a linear relationship to
attenuation coefficients. depend on electron density (and atomic number for xrays). the
correlation was established in scanning phantoms of known density in the range
including lung, muscle, and bone densities.
CT Imaging: computed tomography uses synchronously rotating xray generators
opposing radiation detectors. the distribution of attenuation coefficients can be
, determined if a sufficient number of transmission measurements are acquired and CT
image can be reconstructed.
✔✔patient positioning guidelines - ✔✔- isocentric treatment reduces patient movement
between fields
- isocenter position established using CT with AP,RLAT radiographs to define target
volume
- do not use thick pads or matresses
- noting and reproducing SSD at isocenter
- skin marks should not be sole localization method, because of skin sag and rotation.
- field sizes are to be defined at the isocenter
✔✔autoradiography of encapsulated brachytherapy source - ✔✔a test for gross
nonuniformity of the radionuclide within a source capsule
✔✔LET: characteristics low to high, cell survival curve, dependencies (E, OER, RBE) -
✔✔LET = linear energy transfer in keV/µm, proportional to Q²/V²
low LET: x and gamma radiation, no mass or charge. photon interactions produce
electrons that may deliver dose far off track
medium LET: neutrons, no charge, still highly ionizing because of mass
high LET: alpha particles, have mass and charge, so are very ionizing and produce
many ionizations within a short distance
- cell survival ↓ with ↑ LET
- LET ↓ with ↑ E
- OER ↓ and RBE ↑ (with ↑ LET)
✔✔stopping power - ✔✔locally absorbed energy lost per unit path length.
- "restricted" does not include scatter (restricted < unrestricted)
- s↓ with ↑E, ↑velocity, ↑Z
✔✔scatter radiation characteristics (back and forward scatter) - ✔✔- low energy
photons have more backscatter. max backscatter is at 0.6-0.8mm Cu HVL.
- as photon energy increases, scatter moves more forward.
- dose to any point within a treatment field is due to contributions from both primary and
scatter radiation
- back scatter increases with ↑ in f/s (↑ collimator scatter) and is independent of SSD
✔✔interstitial brachytherapy planning "systems" (methods) - ✔✔Quimby System and
Paris System: uniform placement of needles in row, non-uniform dose distribution
Paterson Parker AKA Manchester System = needle placement defined per calculated
pattern giving nearly uniform dose (max variation ±10% prescription dose)
✔✔tandem and ovoid planning (points A and B) - ✔✔point A: where uterine vessels
cross the ureter -- the main limiting factor for radiation of uterine cervix. = 2cm sup from
os along tandem and 2cm lateral perpendicular to tandem.
