MDCB REVIEW EXAMS PREP QUESTIONS
AND ANSWERS SURE A+
✔✔When comparing compensator-based IMRT and MLC-based IMRT, which one has:
-better resolution?
-less MU?
-less patient dose outside of field?
-larger risk? - ✔✔-Better resolution: compensator based
-Less MU: compensator-based due to less leakage
-Less patient dose outside of field: compensator
-Larger risk: compensator due to wrong one could be used for wrong field
✔✔What are two materials that a compensator can be made of? - ✔✔brass or
aluminum(use Al for low density area like breast)
✔✔What does VMAT stand for and what are 3 things that are modulated during this tx?
- ✔✔-Volumetric Modulated Arc Therapy
-MLC, dose rate, and gantry angle
✔✔Avoidance sectors with VMAT should be a minimum of how many degress? - ✔✔30
✔✔When comparing IMRT and VMAT:
-Which is more conformal?
-Which has a higher hot spot?
-Which has a higher integral dose? - ✔✔More conformal, higher hot spot, and higher
integral dose: VMAT
✔✔What does NCRP 147 discuss? NCRP 151? - ✔✔NCRP 147: diagnostic shielding
NCRP 151: linac shielding
✔✔The primary shielding barrier is a linac vaults is ___ TVL, which is how many inches
and feet of concrete? Secondary barrier (leakage and scatter)? - ✔✔-Primary barrier is
6TVL, which is 96" and 8 feet.
,-Secondary barrier is 2-3 TVL, which is 3-4 feet.
✔✔What is the equation to determine the thickness of shielding needed for a primary
barrier? - ✔✔B=[(P)(D^2)]/[(W)(U)(T)]
✔✔What are the units for workload in the above equation? - ✔✔cGy/week at iso
✔✔What is "T"? and what value is used for the following? (6) - ✔✔"T": occupancy factor
-Work area=1
-Patient exam room= 1/2
-Hallways, employee lounges, exam room=1/5
-Tx vault doors=1/8
-Public bathrooms, closets=1/20
-Parking lot=1/40
✔✔What is the value for design goal of an unrestricted/public area? - ✔✔1mSv/year
0.02mSv/week
✔✔What is the value for design goal of a restricted/occupational area? - ✔✔5mSv/year
0.10mSv/week
✔✔What is the value of leakage from the linac compared to the primary beam? -
✔✔0.1% of the primary
(1 in a 1,000 or 0.001)
✔✔What is the definition of "U"? For shielding "U" is equal to what for secondary
barriers? - ✔✔U=use factor when beam is pointed at a wall
U=1.0
✔✔What thickness of shielding is required for a linac vault door with a maze vs without
a maze? - ✔✔W/ maze: 3/4" of Pb + 4" BP
W/O maze: 6" Pb + 14" BP
✔✔If a 15x or 18x beam is used, what material does the door need to have in it and
where is this material located? - ✔✔Needs to have borated polyethylene plus lead. The
BP is on the linac side of the door and Pb is on other side.
✔✔Discuss neutron production with the following energies:
-6x
-10x
-15x
-18x - ✔✔-6x: not made
-10x: made, don't have to shield
-15x: made, have to shield (0.25)
,18x: made, have to shield (1.00x10^12 neutrons/Gy x-ray)
✔✔Where are neutrons in the linac produced? What energy and QF do they have? -
✔✔-Produced mainly in the target, but also in the FF and collimator
-Average energy of 2mEv and fast neutrons have QF of 20 where thermal neutrons
have QF of 5
✔✔What is the energy of a scattered neutron? What is the energy of a neutron at the
linac door? - ✔✔-1/4 of primary beam energy
-At door=100-200kEv
✔✔With a diagnostic x-ray room, how much lead is used for shielding and how tall is the
wall? - ✔✔1/16th" of Pb, 7ft tall wall
✔✔What is the formal definition of activity? What is the unit? - ✔✔-The decay of 1 gram
of Ra-226
-How much radioactive material
-Curie
✔✔1 Ci=___grams of Ra-226
1 Ci=___dps
1 mCi=___dps
1 uCi=__dps - ✔✔-1 Ci=1 gram of Ra-226
-1 Ci=3.7x10^10 dps
-1 mCi=3.7x10^7 dps
-1 uCi=3.7x10^4 dps
✔✔1 dps=___Bq
1dps=___Ci
1 MBq=___Bq - ✔✔1 dps= 1 Bq
1dps=2.7x10^-11Ci
1 MBq= 1,000,000 Bq
✔✔1 Ci=___mCi
1 Ci=___uCi - ✔✔1 Ci=1,000mCi
1Ci=1,000,000uCi
✔✔1 R=____C/kg air
1 R=___esu/cc air
1 R=___J/kg air
1 R=___rad - ✔✔1 R=2.58x10^-4 C/kg air
1 R=1 esu/cc air
1 R=0.00873 J/kg air
1 R=0.873 rad
, ✔✔1 rad=___erg/g
1 Gy=___J/kg - ✔✔1 rad=100 erg/g
1 Gy=1 J/kg
✔✔Co-60 teletherapy=___Ci
Co-60 gamma knife=___Ci - ✔✔tele=9,000Ci
gamma knife=6,600Ci
✔✔An HDR Ir-192 tx=___Ci
I-131 hyperthyroid tx=___mCi
I-131 thyroid ablation=___mCi - ✔✔-An HDR Ir-192 tx=10 Ci
-I-131 hyperthyroid tx=<30mCi
-I-131 thyroid ablation=100-200mCi
✔✔What is the activity of a Cs-137 source? - ✔✔25 mCi (10mgRa equivalent)
✔✔What is the activity of the following:
-PET injection of FDG/F-18
-1 prostate seed
-Most nuc med
-Cs-137 check source
-Cs-137 as blood irradiation
-Cs-137 for LDR tandem & ovoid (70mgRa) - ✔✔-FDG/F-18=10-15mCi
-prostate seed=0.3mCi per seed
-most nuc med=100uCi-3mCi, most are <5mCi
-Cs-137 check source=10uCi
-Cs-137 as blood irradiation= 50Ci
-Cs-137 for LDR tandem & ovoid (70mgRa)=170mCi
✔✔PET isotopes decay by ___. - ✔✔B+
✔✔What is the energy of annihilation radiation? What is the energy of PET photons
being imaged? - ✔✔511 kEv
✔✔What are 4 isotopes that can be used for PET and why are they used? - ✔✔C-11, N-
13, O-15, F-18
-Used because all have short half-lives
✔✔What is the dose from F-18 and what is it's half-life? - ✔✔-15mCi or 555 MBq
-T1/2=110 minutes
✔✔What are some problems with false uptake when using FDG? - ✔✔-Infection
-Inflammation
AND ANSWERS SURE A+
✔✔When comparing compensator-based IMRT and MLC-based IMRT, which one has:
-better resolution?
-less MU?
-less patient dose outside of field?
-larger risk? - ✔✔-Better resolution: compensator based
-Less MU: compensator-based due to less leakage
-Less patient dose outside of field: compensator
-Larger risk: compensator due to wrong one could be used for wrong field
✔✔What are two materials that a compensator can be made of? - ✔✔brass or
aluminum(use Al for low density area like breast)
✔✔What does VMAT stand for and what are 3 things that are modulated during this tx?
- ✔✔-Volumetric Modulated Arc Therapy
-MLC, dose rate, and gantry angle
✔✔Avoidance sectors with VMAT should be a minimum of how many degress? - ✔✔30
✔✔When comparing IMRT and VMAT:
-Which is more conformal?
-Which has a higher hot spot?
-Which has a higher integral dose? - ✔✔More conformal, higher hot spot, and higher
integral dose: VMAT
✔✔What does NCRP 147 discuss? NCRP 151? - ✔✔NCRP 147: diagnostic shielding
NCRP 151: linac shielding
✔✔The primary shielding barrier is a linac vaults is ___ TVL, which is how many inches
and feet of concrete? Secondary barrier (leakage and scatter)? - ✔✔-Primary barrier is
6TVL, which is 96" and 8 feet.
,-Secondary barrier is 2-3 TVL, which is 3-4 feet.
✔✔What is the equation to determine the thickness of shielding needed for a primary
barrier? - ✔✔B=[(P)(D^2)]/[(W)(U)(T)]
✔✔What are the units for workload in the above equation? - ✔✔cGy/week at iso
✔✔What is "T"? and what value is used for the following? (6) - ✔✔"T": occupancy factor
-Work area=1
-Patient exam room= 1/2
-Hallways, employee lounges, exam room=1/5
-Tx vault doors=1/8
-Public bathrooms, closets=1/20
-Parking lot=1/40
✔✔What is the value for design goal of an unrestricted/public area? - ✔✔1mSv/year
0.02mSv/week
✔✔What is the value for design goal of a restricted/occupational area? - ✔✔5mSv/year
0.10mSv/week
✔✔What is the value of leakage from the linac compared to the primary beam? -
✔✔0.1% of the primary
(1 in a 1,000 or 0.001)
✔✔What is the definition of "U"? For shielding "U" is equal to what for secondary
barriers? - ✔✔U=use factor when beam is pointed at a wall
U=1.0
✔✔What thickness of shielding is required for a linac vault door with a maze vs without
a maze? - ✔✔W/ maze: 3/4" of Pb + 4" BP
W/O maze: 6" Pb + 14" BP
✔✔If a 15x or 18x beam is used, what material does the door need to have in it and
where is this material located? - ✔✔Needs to have borated polyethylene plus lead. The
BP is on the linac side of the door and Pb is on other side.
✔✔Discuss neutron production with the following energies:
-6x
-10x
-15x
-18x - ✔✔-6x: not made
-10x: made, don't have to shield
-15x: made, have to shield (0.25)
,18x: made, have to shield (1.00x10^12 neutrons/Gy x-ray)
✔✔Where are neutrons in the linac produced? What energy and QF do they have? -
✔✔-Produced mainly in the target, but also in the FF and collimator
-Average energy of 2mEv and fast neutrons have QF of 20 where thermal neutrons
have QF of 5
✔✔What is the energy of a scattered neutron? What is the energy of a neutron at the
linac door? - ✔✔-1/4 of primary beam energy
-At door=100-200kEv
✔✔With a diagnostic x-ray room, how much lead is used for shielding and how tall is the
wall? - ✔✔1/16th" of Pb, 7ft tall wall
✔✔What is the formal definition of activity? What is the unit? - ✔✔-The decay of 1 gram
of Ra-226
-How much radioactive material
-Curie
✔✔1 Ci=___grams of Ra-226
1 Ci=___dps
1 mCi=___dps
1 uCi=__dps - ✔✔-1 Ci=1 gram of Ra-226
-1 Ci=3.7x10^10 dps
-1 mCi=3.7x10^7 dps
-1 uCi=3.7x10^4 dps
✔✔1 dps=___Bq
1dps=___Ci
1 MBq=___Bq - ✔✔1 dps= 1 Bq
1dps=2.7x10^-11Ci
1 MBq= 1,000,000 Bq
✔✔1 Ci=___mCi
1 Ci=___uCi - ✔✔1 Ci=1,000mCi
1Ci=1,000,000uCi
✔✔1 R=____C/kg air
1 R=___esu/cc air
1 R=___J/kg air
1 R=___rad - ✔✔1 R=2.58x10^-4 C/kg air
1 R=1 esu/cc air
1 R=0.00873 J/kg air
1 R=0.873 rad
, ✔✔1 rad=___erg/g
1 Gy=___J/kg - ✔✔1 rad=100 erg/g
1 Gy=1 J/kg
✔✔Co-60 teletherapy=___Ci
Co-60 gamma knife=___Ci - ✔✔tele=9,000Ci
gamma knife=6,600Ci
✔✔An HDR Ir-192 tx=___Ci
I-131 hyperthyroid tx=___mCi
I-131 thyroid ablation=___mCi - ✔✔-An HDR Ir-192 tx=10 Ci
-I-131 hyperthyroid tx=<30mCi
-I-131 thyroid ablation=100-200mCi
✔✔What is the activity of a Cs-137 source? - ✔✔25 mCi (10mgRa equivalent)
✔✔What is the activity of the following:
-PET injection of FDG/F-18
-1 prostate seed
-Most nuc med
-Cs-137 check source
-Cs-137 as blood irradiation
-Cs-137 for LDR tandem & ovoid (70mgRa) - ✔✔-FDG/F-18=10-15mCi
-prostate seed=0.3mCi per seed
-most nuc med=100uCi-3mCi, most are <5mCi
-Cs-137 check source=10uCi
-Cs-137 as blood irradiation= 50Ci
-Cs-137 for LDR tandem & ovoid (70mgRa)=170mCi
✔✔PET isotopes decay by ___. - ✔✔B+
✔✔What is the energy of annihilation radiation? What is the energy of PET photons
being imaged? - ✔✔511 kEv
✔✔What are 4 isotopes that can be used for PET and why are they used? - ✔✔C-11, N-
13, O-15, F-18
-Used because all have short half-lives
✔✔What is the dose from F-18 and what is it's half-life? - ✔✔-15mCi or 555 MBq
-T1/2=110 minutes
✔✔What are some problems with false uptake when using FDG? - ✔✔-Infection
-Inflammation
