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16 Cards in this Set
- Front
- Back
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What is the surface dose for a 10 X 10 cm2, 6 MV photon field @ 100 cm SSD?
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15 - 40%
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Source 18F
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Cyclotron
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Source 137CS
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Reactor fuel by-product
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Source 192Ir
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By bombarding 191Ir with neutrons in a reactor
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Source 40K
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Naturally Occurring isotope potassium
Present in human body |
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According to ICRU report 62, when treating the nasopharynx with IMRT, a margin of 0.5 cm around the cord would create a(n) ?
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PRV
Planning Organ at risk Volume |
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It is difficult to visualize small bony structures on an 8-MV portal film because (4 reasons):
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- The Compton process predominates at this energy
- Equal masses of bone and soft tissue will absorb equal numbers of photons - Most of the interactions will be independent of Z -Grids, which improve contrast, are ineffectual at this energy |
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What type of MRI study best helps differentiate CSF fluid from surrounding edema?
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FLAIR
Fluid Attenuated Inversion Recovery |
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The thickness of lead required to shield a 6-MeV electron beam is approximately ______mm
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3 mm
6-MeV electrons are stopped in 3 cm of water, or approximately 3 mm of lead |
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A pregnant woman is treated for Hodgkin's disease with AP/PA 6-MV mantle fields, to a total dose of 4000 cGy. The fetus is 15 cm from the field edge. Without supplementary shielding, the maximum dose to the fetus would be approximately __________ cGy
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24 - 80 cGy
4000 * 0.006 = 24 4000 * 0.02 = 80 The dose to the fetus depends on the distance from the field edge, but from 10 to 20 cm the dose at 10 cm depth is between about 2% and 0.6% of the dose on the beam axis. (AAPR Report No. 50) The dose is made up of patient scatter, head leakage, and radiation scattered from the collimators and blocking trays. |
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A patient has a brachytherapy insertion lasting 36 hours. In the adjacent waiting room the maximum dose rate is 1.9 mR/hr. The required action for this room is:
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No action is required for dose rates below 2 mR/hr
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How many half-lives must a radioactive source be stored before it may be discarded?
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10 half-lives
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MammoSites is prescribed to where?
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1 cm from the balloon's surface
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Transmission factor "B" formula
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B = Pd^2 / W U T
Pd = Permissible dose W = Workload T = Occupancy factor U = Use factor |
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Rule of thumb for dose scattered laterally, from a megavoltage beam
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Maximum photon energy of about 500 KeV
Dose at 1 m is about 1/1000th the dose at the isocenter |
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The annual dose limit to a radiation workers hands?
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500 mSv (50rem)
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