| Terms |
Definitions |
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1966
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Ultrasound
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Prostate seed radionuclides
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I-125
Pd-103
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1970s
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PET and CT
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P-32
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32P
Unsealed source
Decays by negatron emission
Short half life of 14 days.
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X-ray Eavg approximately…
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1/3 Emax
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1899
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Collimation and filtration developed
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Matter
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Anything that occupies space
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Electron beam flatness defined at?
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Dmax
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Paris dosing system
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Brachytherapy dosing system:
Uniformly spaced source lines of equal length and strength.
Dose prescriptions are to 85% ofthe average of the local dose minima between neighboring needles.
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Strontium-89
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89Sr
Unsealed source.
Produced in a nuclear reactor as a by-product of the fission process.
Decays by negatron emission
Half life of 50 days.
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Forms of electromagnetic energy
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X-rays
Radio waves
Microwaves
Ultraviolet light
Infrared light
Visible light
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1920
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ASRT - (first professional organization) developed
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Quimby dosing system
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Brachytherapy dosing system:
Uniform distribution and uniform strength of sources.
Results in a non-uniform dose distribution.
Dose specified 3mm beyond periphery of volumes.
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Neutron detection
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Boron bombarded with neutrons transformes to a lithium atom plus alpha particle.
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X-ray filter
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Improves resolution in diagnostic imaging.
Placed over the film to block scattered x-rays (scattered x-rays come from the Compton effect)
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Radiochromic film
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Different (and newer than) radiographic film. It also determines absorbed dose.
Doesn't require developing.
More expensive.
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Memorial dosing system
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Brachytherapy dosing system:
Uniform distribution and uniform strength of sources.
Results in a non-uniform dose distribution (like Quimby).
Dose specified at the edges of the volume (Quimby uses 3mm beyond periphery of volume).
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Photon attenuation equation
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N(x) = N0 e-μx.
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Auger electron
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Electron transitions to inner shell.
Energy from transformation is transferred to outer-shell electron which is then ejected.
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Isobar
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Protons + Neutrons stays the same.
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Radioactive decay equations
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A(t) = A0 e-λt.
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Alpha decay
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Emission of a helium nucleus.
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The largest component of natural environmental radiation is ________.
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Radon
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1921
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First grid to remove scatter radiation
(Potter-Bucky grid)
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Energy is......
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The ability to do work
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mA = the number of ????
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Electrons
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Intra-leaf leakage
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Can be 30%.
Probably lower with tongue-and-groove MLC design.
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Indirectly ionizing
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Particles with NO charge (neutrons, photons, etc.) that create direct ionizing particles that deposit energy into matter.
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Annihilation
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An electron and positron collide to create two photons, of at least 0.511 MeV each.
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Calorimetry
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Measures the heat increase after a substance is irradiated.
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Neutron detectors
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Based on the following rection
the alpha particle from this rxn is detected.
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X-ray Emax depends on…
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voltage of tube (kVp)
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The first medical x-ray film was produced when?
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1896
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Chemical energy
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Energy released by a chemical reaction
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Geometric penumbra
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Caused by finite size of source. Increases with increased SSD.
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Bremsstrahlung x-ray
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Created when an electron comes in close proximety with a nucleus, changes direction/decererates, and a photon is released. Probability ≈ Z2
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Occupancy factor (T)
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Occupancy factor (T) gives the fraction of operating time during which the area of interest is occupied by the individual.
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Three types of personal dosimeters
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TLD badge
Film badge
Electronic dosimeter
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Beta-minus decay
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Neutron --> proton + electron + anti-neutrino.
Occurs in nuclei with a high n/p ratio. Example of an isobaric decay (same number of nucelons)
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Electron capture
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proton + inner shell electron --> neutron + neutrino.
This creates a hole in an inner shell, so the atom creates either a characteristic x-ray, or an Auger electron. Competes with Beta-plus decay.
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Shipping labels for radioactive sources
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Type Surface dose Dose rate at 1m
White 0-0.5 mR/hr N/A
Yellow II 0.5-50 mR/hr 0-1 mR/hr
Yellow III 50-200 mR/hr 1-10 mR/hr
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Gamma emmision
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A metastable atom can undergo isomeric decay with gamma emission, which is simply the emission of a gamma ray from the nucleus.
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Internal conversion
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A metastable atom can undergo isomeric decay with internal conversion, which when a nucleus transfers excess energy to an orbital electron, which is then ejected (that takes away energy). This results in a characteristic x-ray or Auger electron.
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A special type of radiation that includes x-rays
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Ionizing radiation
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What year did Roentgen win the Noble Prize for physics?
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1901
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2 main categories of Ionizing Radiation
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Natural environmental radiation
Man-made radiation
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X-ray voltages are measured in ???
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Kilovolt Peak (kVp)
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Negligible individual dose
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dose below which further efforts to reduce radiation exposure are unwarranted
0.01 mSv/yr
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Primary collimator goal…
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Goal is to prevent radiation from leaking from machine head.
Projects a 40cm circular field towards the isocenter.
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Full wave rectification
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flips negative part of cycle to positive.
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LET - range
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Range is the distance a charged particle travels before it's stopped in a material.
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Radiation exposure
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Charge of the ions of one sign produced in air by photons when all the electrons are completely stopped in air.
Unit = Roentgen = R.
1 R = 2.58 x 10-4 C/kg air.
ONLY defined in air.
ONLY measured with photons.
ONLY defined up to energy of 3 MV.
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Beta-plus decay (emission)
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Proton --> neutron + positron + neutrino.
Occurs in low n/p nuclei. Example of isobaric transformation.
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What is the scientific unit of mass?
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The kilogram (kg)
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Internally deposited radionuclides
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Mainly potassium -40 which is a natural metabolite (part of the metabolism)
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Use factor (U)
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Use (U) factor is the fraction of operating time during which radiation is striking a particular barrier.
Walls = 1/4
Floor = 1
Ceiling = 1/4-1/2
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Photon beam flatness defined at?
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For photons, flatness measured over 80% of field size at 10 cm depth.
This creates horns (higher doses at edge of beam) at shallower depths.
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Anode facts in diagnostic x-ray machines
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Universal problem is heat dissipation.
Solutions: rotating anode, dual focal spots (one larger for blurry images, and one smaller for fine images).
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Parent-daughter equilibream - secular
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Daughter half life is much shorter than parent half life (or daughter decay constant is much longer than parent), then there is a gradual buildup until the daughter activity equals the parent activity.
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Dose rates for...
LDR
MDR
HDR
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Low dose rate <2 Gy/hr
High dose rate >12 Gy/hr
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Define total ionization
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The total number of ion pairs produced by a particle or electromagnetic wave.
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The orbital electron and the atom from which it was separated is called ________.
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An Ion Pair
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Characteristic vs Auger by Z
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High Z --> emission of characteristic x-ray more probable.
Low Z --> emission of Auger electron more probable.
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Electron beam rules of thumb
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D90% = E/4.
D80% = E/3.
Max range = E/2.
Surface dose increases with increasing energy.
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Linear energy transfer (LET)
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The LET represents the rate of energy loss per unit path length (keV/μm) in collisions in which energy is "locally" absorbed, rather than being carried away by energetic secondary particles. LET is higher with lower energy particles.
60Co 0.3 keV/μm
250 keV x-ray: 3 keV/μm
3 MeV x-ray: 0.3 keV/μm
1 keV electron: 12 keV/μm
1 MeV electron: 0.25 keV/μm
2.5 MeV neutron: 20 keV/μm
5 MeV alpha: 100
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Exposure rate formula for radionuclide
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X = ΓA/d2
where X = exposure rate
Γ = gamma constant for radionuclide (R-cm2/mg-hr, or R-cm2/mCi-hr)
A = activity of radionuclide (mg or mCi)
d is the distance from the source (cm)
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List 3 man-made sources of radiation.
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a X-ray machinesb Low energy radioactive tracers for diagnosis of diseasec. High-energy radioactive isotopes used for treatment of diseases such as cancer.
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The only forms of electromagnetic radiation with enough energy to ionize.
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X-rays, gamma rays and ultraviolet light
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Why to put electron collimators close to skin?
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Because electrons scatter easily in air.
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Mass deficiency of nucleus
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The sum of the mass of the neutrons and protons in a nuceus is more than the mass of the nucleus. The difference is the "binding energy of the nucleus", denoted by: E = mc2
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X-ray currents are measure in ???
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Milliamperes (mA) where (A) is a measure of electric current
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As field size increases, the PDD _____
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As field size increases, the PDD increases.
This is because of increased scatter.
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Electron inhomogeneity around a high Z material occurs...
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High dose occurs before the high Z material (like metal implant) due to backscatter.
Low dose occurs after the high Z material.
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Diagnostic x-rays contribute approx ? mrem/yr
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39 mrem which is the largest source of Ionizing Radiation
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1980s
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MRI
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1942
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First automatic processor
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PET
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positron emission tomography (PET)
18F decays and emits a positron that travels a short distance before it interacts with an electron and annihilates, creating two 0.511 MeV photons that travel in opposite directions.
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Samarium-153
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Unsealed source (quadrimet)
Decays via negatron emission.
Half life of 2 days (47 hours).
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REM
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Radiation Emitted to Man
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Power rule (equation)
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P = I*V
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SPECT
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Single Photon Emission Computed Tomography
Most commonly uses 99mTc, which emits a 104 KeV photon.
Basic idea is that your body emits the photons, which are then projected onto a collimator which absorbs any scattered radiation. The gamma rays then causes scintillation (generating a light ray) which is then detected.
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Dose limit:
Lens of eye
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150 mSv/yr
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NRC misadministration
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Radiopharmaceutical differs by >20%
Total teletherapy dose off by >20%
Weekly teletherapy dose off by >30%
SRS dose off by >10%
Brachytherapy dose off by >20%
Wrong patient treated
Wrong treatment site
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eV
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electron volts (used in radiography)
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Waveguide
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Directs the microwaves towards the accelerator structure.
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Paterson-Parker, Manchester dosing system
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Brachytherapy dosing system:
Non-uniform source distributions resulting in a uniform dose distribution.
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Dose from TMR equation
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Dd2 = Dd-iso*(TMRd2/TMRd-iso)*(SAD/(SSD+d2))2.
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Direct ionization
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Particles with charge (protons, electrons, etc.) that deposit energy directly into matter.
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Cobalt 60
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60Co
Half life 5.26 yrs.
Rate constant = 13 R-cm2/mCi-hr.
Gammay ray energy = 1.17, 1.33 (1.25 avg).
Specific activity = 200 Ci/g
Created by: neutron bombardment
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PDD equation
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Dd2 = Dd1 * (PDDd2/PDDd1).
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Gieger-Mueller counter
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good choice for qualitative measurements of radiation.
Bad for quantitative measurements
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Kerma
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Photon interacts with matter while transferring some or all of the photon energy to the electron in the form of kinetic energy.
Kerma is the energy transfer from uncharged particles (photons) to charged particles (electrons).
Kerma = kinetic energy released in matter.
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1948
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Image intensifier tube developed for fluoroscopy screens
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When were x-rays discovered?
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November 8, 1895
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Dose limit:
general public (infrequent & continuous)
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Infrequent exposure: 5 mSv/yr
Continuous of frequent exposure: 1 mSv/yr
Extremities, skin, lens of eye 50 mSv/yr
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Dose limit:
Embryo-fetus
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Total: 5 mSv
Monthly: 0.5 mSv
To abdomen survace: 2 mSv
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Fusion
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Creation of larger atoms from smaller atoms.
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Compton scattering
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Incident photon interacts with an electron to cause ejection, and a fraction of the photons energy is absorbed. Proportional to 1/E, independent of Z.
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Describe the interaction processof electromagnetic radiation withmatter.
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Photoelectric Effect,Compton Scattering, and Pair Production.
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1917
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Cellulose nitrate film base is widely adopted
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Magnetron and Klystron function
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Magnetron makes microwaves that accelerate electrons. Klystron amplifies microwaves.
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Effective dose equivalent
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Because whole-body exposure is not usually uniform, the effective dose equivalent is defined as "the sum of the weighted dose equivalents for irradiated tissues".
Measured in Sievert (Sv).
Tissue weighting factors
Gonads = 0.2???
Bone marrow, breast, colon, lung, stomach = 0.12
Bladder, esophagus, gonads, liver, thyroid = 0.05
Bone surface, brain, kidneys, salivary glands, skin = 0.01
Remainder tissues = 0.10
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Exposure from x-rays
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Chest x-ray: 8 0.1mSv
CT: 10 mSv
Coast-to-coast airplane trip: 0.05 mSv
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Radium 226
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226Ra
Half life = 1600 yrs.
Rate = 8.25 R-cm2/mCi-hr.
Decay's by alpha and beta decay.
Mean energy = 0.83 MeV.
Specific activity = 0.98 Ci/g
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Cesium 137
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137Cs
Half life = 30 yrs
Decays by beta and gamma emission.
Rate = 3.26 R-cm2/mCi-hr.
Energy = 0.663 MeV.
Specific activity = 50 Ci/g.
Produced as a by-product of fission process in nuclear reactor.
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Dose limit:
radiation worker
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Annual: 50 mSv/yr
Cumulative: 10 mSv x age
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Annual average exposure from diagnostic radiology.
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diagnostic x-rays 0.4 mSv.
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Shielding equation
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D = B*(WUT)/d2.
where D is the dose,
B is the barrier transmission factor,
W the workload,
U the use factor,
T the occupancy factor,
and d the distance
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Quality factor definition
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Used in radiation protection (similar to RBE). Take into account the radiobiologic effect of different types of radiation.
Radiation type: quality factor
X-ray, γ-ray, electron: 1
Neutrons (thermal): 5
Neutrons (fast): 20
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Stochastic effects
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Random in nature and possess no threshold,
such as cancer.
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Beta-decay
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Refers to emission of an electron, or positron from a nucleus. Does not refer to ejection of an electron from an electron shell.
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Thermal energy
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Energy of motion at the molecular level (kinetic energy of molecules) - molecules in motion
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Matter that intercepts radiation and absorbs part or all of it is said to be
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Exposed or irradiated
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IMRT sliding window technique
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Collimator leaves slide across the field, and hold thier positions until the required fluence is achieved.
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Point A
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2cm above and 2cm lateral to the cervix.
Typical dose rate to pt A is 50 cGy/hr.
Point B is 3cm lateral to point A
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Half life
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A(t) = A0 e-λt.
1/2 = e-λt.
t1/2 = ln2 / λ = 0.693 / λ.
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Treatment room design:
Radiation rate max for
Controlled area
and
Uncontrolled area
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Controlled area = 1 mSv/wk
Uncontrolled area = 0.1 mSv/wk
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Neutrons in radiation therapy
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Often made by accelerating deuterons in a cyclotron, and then colliding the deuteron into Berylium target to strip neutrons.
Problem is that they have a wide penumbra because of difficulty collimating the beam.
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Production of diagnostic x-rays
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Make electrons: heat cathode, which releases electrons via thermionic emission.
Accelerate electrons: potential difference between cathode and anode accelerates electrons.
Decelerate electrons: electrons collide with target (tungsten), and part of their energy is released as x-rays.
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Focal spot
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Angling the x-ray target to reduce the focal spot, thus increase image quality
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X-ray tube current predicts
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directly proportional to quantity of x-rays produced.
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Absorbed dose
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After collision of a photon with an atom, a primary electron is released.
Absorbed dose is the energy absorbed in a material per unit mass.
1 Gy = 1 J/kg = 100 rad.
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Optimal hinge/wedge angles
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The optimal wedge angle (θ), and hinge angle (φ), come from the following equations:
θ = 90 - φ/2.
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Dose equivalent definition…
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Equivalent dose = dose * quality factor.
Where quality factor represents the relative amout of linear energy transfer by various types of ionizing radiation.
X-ray, electrons, protons --> quality factor = 1.
Thermal neutrons (<10 keV) --> quality factor = 5.
Fast neutrons (10 keV-2MeV) --> quality factor = 20.
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Photoelectric effect
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The photon is absorbed by an orbital electron, which is then ejected from the atom.
Ephotoelectron = Ephoton - Ebinding.
Probability is proportional to Z3/E3.
Electron vacancy filled (characteristic x-ray, or Auger electron).
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Describe the process of ionization
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Radiation passing through matter transfers energy to the target atom and may cause the ejection of orbital electrons.
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Describes the mass of an object in a gravitational force
|
Weight
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What type of tube was Roentgen using when he discovered x-rays?
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Crookes tube
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Radiation scintillator detectors
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...based on the principle that when an excited or ionized ion undergoes de-excitation or recombination, energy is released. In some materials this energy is released as visible light (called scintillation). The radiation detectors that they are used to detect this light are called scintillation detectors.
Very sensitive to small amounts of radiation.
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Relative biologic effective (RBE) dose
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RBE dose describes the relative biologic effectiveness of a defined dose of radiation.
Defined as the absorbed dose times the RBE.
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Atomic mass number
|
AZX
Atomic mass number = A = number of protons + neutrons
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Parent-daughter equilibream - transient
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Daughter half life is only slightly shorter than parent half life (or daughter decay constant is barely shorter than parent), then there is a gradual buildup until daughter exceeds the activity of parent (but both slope downward).
Ad = Ap * (t1/2,p / (t1/2, p - t1/2, d)).
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Neutron reactions (by neutron bombardment)
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(n,γ): neutron absorbed into nucleus, and gamma ray emitted.
(n, α): neutron absorbed and alph emitted.
(n, p): neutron absorbed and proton emitted.
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Back scatter factor definition
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Back scatter factor (BSF) = exposure at phantom surface / exposure at same point when no phantom present
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Define electron volt
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The amount of energy gained by an electron when it is accelerated through a potential of 1 volt.
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Electrical energy
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Work that can be done when an electron or electronic charge moves through an electric potential
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Dose equivalent units
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Seivert (Sv)
1 Sv = 1 Gy (for photons and electrons)
100 rem = 1 Sv.
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Shutter error with Cobalt 60
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extra dose given when 60Co source moves from on to off position at beginning and end of treatment.
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Describe gamma and x-ray radiation with respect to its mass,charge, energy, source, velocity,and range in air.
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b. Electromagnetic radiation has no mass.c. Electromagnetic radiation has no charge.d. Energies1) Gamma rays emitted by natural radioisotopeshave energies between 0.04 and 3.2 MeV with fission product gammas ranging higher.2) X-rays generally exist at lower energies, but there is some overlapping. X-rays are commonlyemitted in the lower energy range, 0 to 88 KeV.e. Sources1) Gammas originate from nuclei, which are in an excited state.2) X-rays are emitted when an electron drops to a lower energy orbit.f Electromagnetic radiation travels at the speed of light (186,000 miles/sec).g. Range1) The range of high-energy electromagneticradiation is theoretically infinite since the intensityof the radiation decreases exponentially as itpasses through material.
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Einstein's mass-energy equivalence
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E=MC2
E = energy
m = mass
c = is the speed of light in a vacuum
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Tissue maximum ratio (TMR)
definition
|
TMR = dose at depth d in phantom /
dose at depth dmax in phantom.
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Mayneord F-factor
what is it, and what is the equation?
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The Mayneord F-factor is used to determine the PDD when changing SSD.
F = ((SSDnew + dmax)/(SSDold + dmax))2 *
((SSDold + d)/(SSDnew + d))2.
Then it follows:
PDDnew = PDDold * F.
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Explain uses of laboratory radiation sources in connection with radiation detection instruments.
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a. Neutron sources – startup of nuclear reactorsb Radiography – X-rays to detect material and welding flaws.c. Radioactive sources – alignment and calibration of radiation detection equipment.
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Tissue maximum ratio (TMR)
equation with PDD
|
PDD = TMR * ((SSD + dmax)/(SSD + d))2(PSFd/PSFdmax).
Because (PSFd/PSFdmax) is close to 1, it is often eliminated.
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Electron shells
(order and max number of electrons per shell)
|
Order of electron shells: k, l, m, n, o
Max number of electrons per shell = 2n2,
where n is the order number.
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Percent depth dose at 10cm at 100cm SSD for different energies
|
CO-60: 56%
4 MeV: 61%
6 MeV: 67%
10 MeV: 73%
20 MeV: 80%
25 MeV: 83%
34 MeV: 88%
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Describe beta radiation withrespect to its mass, charge,energy, source, velocity, andrange in air.
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a The charge is minus oneb Mass is identical to an electron which is 9.1 x 10 -28grams or 0.00055 amu.1) A beta minus particle is 1/1840 the mass of a neutron.c. Energy level ranges between 6 KeV and 4.81 MeV.d. Sources1) Most fission products at the plant are neutronheavy (discussed later in Chapter 4) and thusbeta minus decay.2) These sources are usually contained within ametal pipe or tank, which provide adequateshielding to stop most high-energy beta particles.e Betas exist at about 99% the speed of light.
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Tissue air ratio (TAR)
Definition and dependencies
|
TAR is the dose at depth d in phantom /
dose in free space at the same point.
TAR varies with respect to:
Beam energy
Depth
Field size
TAR is independent of:
SSD
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