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MPhy

Medical

CTP = 273+C/295 x 760/P
"Electrons, formula to find 50% dd" E/2.33
Clinical range Electrons E/3 - E/4
max energy of scattered photon at 90deg 511 keV
rest energy proton 938 MeV
Daily check, QA, gamma knife timer, safety checks
List the KiloV units Grenz, contact, superficial, ortho
QA, how often check output for gamma knife? monthly
1 AMU = ?? MeV 1 AMU = 931 MeV
How far do b+ travel in tissue? 0.5 cm/MeV
How to calculate change in dose due to pt seperation parallel opposed 6xsw remember 3% per cm
Conv QA for photons is... 2% or 2mm
Conv QA for electrons is... "3%, 3 mm"
Dose under %HVT kidney block "10 - 20% depending energy, FS"
HVT superficial units 1 - 8 mm Al
Range energy ortho 150 - 500 KvP
SSD ortho 50 - 70 cm
Dose monitoring system in beam path... dose rate, integral dose, beam symmetry
tx distance superficial units SSD 15 - 20 cm
What determines beam penumbra? source size secondary collimator
Conv E [MeV] to wavelength l [meters] 1.24/l
Activity per unit mass (G/m) = specific activity
increase eff xray unit Voltage Z
"Supervoltage therapy, energy" 500 - 1000 kV
energy xrays van der Graff 2 - 10 MV
What magnifies microwaves in linac? klystron
Describe grazing hit Compton effect photon goes forward electron at 90° w/T=0
Describe direct hit Compton Max energy electron, which travels fwd photon @ 180°
Max energy Compton photon scattered @ 180° me/2 = 0.255 MeV
Max energy Compton photon scattered @ 90° me =0.511 MeV
max Energy compton photon scattered @ 0° energy initial photon
total KE available for e+e- pair for pair production hf - 2*me = hf - 1.02 MeV
"Annihilation radiation, energy each annihilation photon" 0.511 MeV
Describe the photons created in annihilation radiation Two 0.511 MeV particles scattered in opposite directions
threshhold kVp for xray tube for Compton effect 90 kVp
define stopping power rate of kinetic energy loss per unit path length
Number of elements = 103
Radioactive threshold in Z = 82
Name the 3 naturally occuring radioactive series "uranium, actinium, thorium"
define: equilibrium isotopes ratio of daughter to parent activity constant
KE alpha particles 5 - 10 MeV
Describe K capture "Electron capture of electron in orbit closest to nucleus, competes with positron decay"
Define fission Bombarding high atomic elements with neutrons resulting in nuclear disintegration
Describe fusion low mass nuclei combined to produce one nucleus
"formula exposure rate, C =" gamma X activity / ISF
define apparent activity in terms of encapsulated 0.5 mm Pb radium at 1-m
Gamma factor radium 8.25 Rcm2/mCi-hr WATCH UNITS
converting mCi to mg-Ra equiv strength = gamma/gamma-Ra x app activity mCi
radial dose important for which low energy sources? I-125 P-103
Which brachy system implants more dose at periphery? PP
When do you need more radium in Quimby sys than in PP? When dose RX at min
Which system uses long lines sources for implants? Paris
Which implant system calcs RX from basal dose? Paris
What 3 things needed for implants according ICRU? dim target ref kerma ref pts
Decay I and Pd e- capture
Which nuclides anisotrophy factors? I 125 Pd 103
rad protection stds for nuclear reactors set by this US body NRC
stds for naturally occuring radionuclides set by this body state
recomm adhered to by states set by this body NCRP
Factor that converts dose to bio effect Q
Negligible risk factor 0.01 mSv
occup dose lens 150 mSv
formula for exposure from brachy sources for rad safety and barrier Thickness X [R] = gamma x activity x time x B / ISF
Formula to calc TVLs
Formula to calc thickness of wall from TVL - TVL log (B)
"If B = 10^-5, how many TVLs?" 5
5 TVLs of concrete for 6X 168 cm
Year R adopted ICRU as unit 1928
Year Cobalt 60 1951
Si unit X C/kg
Clinical unit X r
Energy limit free air ionization measurements 3 MeV
Density of mass in air in thimble chamber increases with... decreasing T increasing P
TG report concerning measurements absorbed dose 51
In tx breast, dose at chest-lung interface" 80% E = depth x 3
Ripple in 1) ~0%
1) constant 2) 5-10%
2) three phase 6 pulse 3) 4%
3) three phase 12 pulse
Tungsten k edge 70 KeV
increase of mAs of 100% is equal to what increase of kVp 15%
Fluoroscopy x ray tube currents 1-6 mA
Radiography/CT xray tube currents ~100s mA
Focal spot in CR Small 0.6 mm Large 1.2 mm
Typical anode angle 15 degrees
At what energy are photon and compton equal 25 keV
Screen film needs how many uGy to blacken? 5 uGy
Entrance Air Kerma for 1) chest 2) skull 3) abdomen 1. 0.1 mGy 2. 1.5 mGy 3. 3 mGy
State regualtions for HVL >2.5 mm Al at 80 kVp
OD of the following values allows what percentage of light to pass through OD 1 OD 2 OD 3 1 = 10% 2 = 1% 3 = 0.1%
Bucky Factor for mammo 2:1
Bucky factor for CR 5:1
Grid ratio for mammo 5:1
Grid ration for normal CR 10-12:1
Bits in a byte 8
how many gray levels in 8 bits 256
How many MB do the following images take up 1) CXR 2) Single Mammo image 3) Digital photospot 4) MR (single slice) 1) CXR 10 MB 2) Mammo 24 MB 3) Digital photospot 2 MB 4) MR 1/8th mammo
Resolution of 1) Screen/film 2) CR 3) Digital Mammo 4) Conventional Mammo 5) Fluoro 6) CT 7) MR 1) Screen film 5 lp/mm 2) Digital CR 3 lp/mm 3) Digital Mammo 7 lp/mm 4) Conv Mammo 15 lp/mm 5) Fluoro 1 lp/mm 6) CT 0.7 lp/mm 7) MR 0.3 lp/mm
Occupational Dose Limit (whole body) 50 mSv/y
Occupational Dose Limit (Skin/extremity/any organ other than eye) 500 mSv/y
Occupational Dose limit (eye) 150 mSv/y
Dose limit to general public 1 mSv/y
Dose limit to fetus 0.5 mSv/ month or 5 mSv entire pregnancy
Doubling dose for hereditary effects 1 Gy
Dose to cause skin erythema 2 Gy
Half life of Tc 6 h
LD 50/60 for adults ~ 3.5 Gy
Temporary Epilation 3 Gy
Permanet Epilation 7 Gy
Dose to cause catarct (acute and accumulative) acute 4 Gy accumulative 8 Gy
Sterility in males (temporary and permanent) 2.5 and 5 Gy
Sterility in females 1.5 and 6 Gy
Dose needed for hematopoetic syndrome >2 Gy
Dose needed for GI syndrome >10 Gy
Dose needed for CV syndrome >50 Gy
Most sensitive period for fetal development organogenesis (8-15 weeks)
How much power does a CT scanner use with a tube voltage of 120 kV and current of 830mA? 100 kW
What is the focal spot size of CT x-ray tubes? 1 mm
What is the power that a small focal spot x-ray tube in a CT scanner can tolerate? "25 kW, as compared to 100 kW for a larger focal spot"
What are typical anode heat dissipation rates? 10 kW
What are typical anode heat capacities? 4 MJ
What is a Straton tube? rotating envelope vaccum vessel?
What is the advantage of a Straton tube? "High heat dissipation rates, > 60 kW"
How is the anode-cathode axis positioned to reduce heel effect? Perpendicular to the image plane
What type of filters are used in CT? Cooper or aluminum
What is the typical filtration for a CT x-ray tube? 6 mm Al
What is the typical aluminum half value layer filtration of a CT beam? 10 mm Al
What does heavy filtering reduce on the CT image? Beam hardening effects
What is used to minimize dynamic range of exposures at the detector? Bow-tie filter
How do bow tie filters work? "Attenuate little in the center, more with increasing distance from the central ray"
What are bow tie filters made of? Teflon
What defines the section thickness on a single-slice scanner? Collimator
What does collimation define on MDCT systems? Total beam width
What is the beam width of a 64 slice scanner? 40 mm
What is the beam width of a 320 slice scanner? 160 mm
What does a high-resolution comb do? Reduce detector aperture width and improve resolution
How much dead space is between CT detectors? 0.1 mm
What is the geometric efficiency for detectors that are 1mm wide? 90%
What light detectors do CT scanners use? PMT and photodiodes
What are two desirable signal characteristics of CT detectors? Good temporal response and rapid signal decay
What is the quantum efficiency of CT detectors? > 90%
Scintillators convert what % of absorbed x-ray energy to light energy? 10%
What is the most common material used in solid-state detectors? "CdWo4, cadmium tungstate"
What are common materials used in CT detectors? "cadmium tungstate, cesium iodide, calcium fluoride, bismuth germanate"
What is the typical long axis width of a CT detector array? 0.6 mm (64 x 0.6 mm = 40 mm)
About how many detectors does a typical detector array have? ~ 800
What are two common interpolation algorithms for helical CT? linear and z-filtering
What interpolation algorithm restricts pitch to a few fixed values? Linear
What is the main advantage of z-filtering? Allows greater selection of pitch
What are the two fields of view in a dual-source CT? 50 cm and 26 cm
Temporal resolution in dual source CT is ___ the rotation time and ____ the rotation time of a single source scanner. "1/4, 1/2"
About ____ the energy is deposited during a single tube rotation. 1/2
"In head CT, the central and surface doses are _____." similar
"In body scan, the surface dose is ____ that obtained in the center." twice
What are two phantoms used in CT dosimetry? "16 cm acrylic head, 32 cm acrylic body"
What are CTDI values measured in? "air kerma, mGy"
What is a typical CTDIair for commercial scanners? 0.25 mGy/mAs
How to calculate weighted CTDI (CTDIw) 2/3 CTDIp + 1/3 CTDIc
"If pitch is < 1.0, how does that affect dose?" Increases it
How is volume (CTDIvol) calculated? CTDIw/pitch
How to calculate dose length product? CTDIvol x scan length
Increasing tube voltage from 80 kV to 140 kV increases the dose _____ fivefold
What is the mean CTDIw for adult head and adult abdomen? 58 mGy and 18 mGy
What is the mean CTDIvol for a 5-year old pediatric abdomen? 16 mGy
Increasing patient size by 20 to 100 kg reduces x-ray beam penetration by ____ 30
"What are typical mAs for the following adult exams? head CT, chest CT, abdominal CT" "300 mAs, 150 mAs, 200 mAs"
CT can detect lesions that differ abourt ____ % from surrounding tissues. 0.3%
How big are pixels in CT relative to radiography? three times large; 0.6 mm compared to 0.2 mm
Single chest CT radiation dose risk is comparable to ____ chest x-rays. 100
What phase of cardiac cycle is cardiac imaging best performed? Diastolic
Retrospective cardiac gating ____ dose by approximately ____ times when compared to prospective. "increases, 3 times, because of lower pitch"
"Lower energy photons are preferentially absorbed, causing the beam to become more penetrating. What kind of artifact is this?" Beam hardening
How is X-ray intensity measured? Intensity is measured in Roentgens (R or MGy a) or milliroentgens (mR) and is termed the x-ray quantity.
What is a roentgen (mGy a)? A measure of the number of ion pairs produced in air by a quantity of x-rays.
What are some other names for X-ray intensity? "X-ray quantity, radiation exposure, X-ray quantity."
Roentgen formula 1R=2.58 x 10(-4) C/kg
What is x-ray quantity? The number of x-rays in the useful beam.
What are the factors affecting x-ray quantity? "Milliampere-seconds (mAs), Kilovolt Peak (kVp), and Distance."
Milliampere-seconds (mAs) X-ray quantity is directly proportional to mAs.
mAs x-ray quantity formula I1/I2 = mAs1/mAs2
kVp X-ray quantity varies approximately as the square of the change in kilovolt peak (kVp).
kVp x-ray quantity formula I1/I2 = (kVp1/kVp2)2
Distance X-ray quantity varies inversely with the square of the distance from the target (the inverse square law).
Distance x-ray quantity formula I1/I2 = (D2/D1)2
X-ray exposure of a patient can be estimated to a reasonable approximation with the use of what equation? x-ray quantity (mR) = k (mAs) (kVp)2/D2
"When the mAs is increased, x-ray quantity: " Increases proportionately.
"When the kVp is increased, x-ray quantity: " Increases in proportion to kVp2.
"When distance is increased, x-ray quantity at that distance: " Decreases in proportion to distance squared.
"When x-ray tube filtration is increased, x-ray quantity: " Decreases
"In general, x-ray quantity will increase with a/an: " Increase in kVp
X-ray quantity is usually measured as which of the following? Exposure in roentgens.
X-ray quantity can be measured in which of the following? Gy a
"Another meaning of ""x-ray quantity"" is x-ray: " Intensity
Factors affecting x-ray quantity "Filtration, kVp, mA, and Time"
"To maintain a constant optical density, what percentage increase in kVp should be accompanied by a reduction of one half in mAs? " 15%
An extremity radiograph requires 5 mAs and results in an exposure of 18 mR. What will be the exposure if the technique is changed to 7 mAs? 25 mR
"An abdominal view is taken at 82 kVp and results in a patient exposure of 132 mR. To improve contrast, the kVp is reduced to 74 with no change in mAs. What is the new patient exposure? " 108 mR
"A portable chest x-ray is taken at 90 cm SID, and the patient exposwure is 28 mR. What will the eposure be if the distance s increased to 180 cm and there is no accompanying technique change? " 142 mR
"The output intensity for an x-ray imaging system operated at 70 kVp/400 mA and 50 ms is 70 mR. If the mA selector is changed to 600 mA and the exposure time is increased to 80 ms, what will be the output intensity? " 52
Which of the following is the most appropriate measure of x-ray beam quality? HVL
HVL definition That thickness of an absorber that will reduce the x-ray intensity to one half its original value.
The quality of an x-ray beam is principally a function of which of the following? kVp
The HVL is affected principally by a change in which of the following? kVp
"When filtration is added to an x-ray tube, which of the following increases? " Radiation quality
Which of the following is the probable HVL of a radiographic x-ray beam at 70 kVp? 5.0 cm soft tissue
As filtration is added to an x-ray beam: Low energy x-rays are removed more readily than high
An increase in mAs will increase which of the following? X-ray quantity
It is often stated that mAs controls quantity and kVp controls: Quality
"However, it should be clear that mAs controls quantity and kVp controls: " Quality and quantity
If the mA during fluoroscopy is increased by 25%: The scatter exposure to the operator is increased by 25%
A minimum HVL is required for diagnostic x-ray beams because: A lower HVL would result in an increased absorbed dose to the patient with no improvement in image quality
An x-ray beam can be made to have higher effective energy if which of the following occurs? Filtration is added
Filtration will increase: X-ray beam quality
Reducing kVP will: Soften the x-ray beam
Adding filtration to an x-ray beam will: Increase x-ray quality
"A radiographic tube has 0.5 mm Al inherent filtration, 1.0 mm Al added filtration, and 1.0 mm Al filtration in the light-localing collimator, Therefore, the total filtration is: " 2.5 mm Al
A representative radiographic tube has 0.5 mm Al inherent filtration and 2.0 mm Al added filtration. An additional 1.0 mm Al filtration will: Harden the x-ray beam
"Diagnostic x-rays, Grenz rays, Megavoltage x-rays, Orthovoltage x-rays, or Supervoltage x-rays " Grenz rays
The HVL is defined as: A thickness of attenuator that will halve x-ray quantity
"To measure HVL, which of the following is required? " A collimator and Aluminum abosrbers
"As the HVL of a beam increases, its penetrability: " Increases
"If increasing the kVp increases the HVL, x-ray quantity will: " Increase by kVp2
"If the HVL is increased by the addition of 1 mm Al, x-ray quantity will: " Decrease
"At 70 kVp, the x-ray beam is atttenuated in soft tissue approximately: " 5% /cm
There is a 75% chance that an x-ray will be attenuated by 2 mm lead. The HVL is: 1.5 mm Pb
What occurs when the small rather than the large cathode coil is energized? smaller effective focal spot
Added filtration affects the x-rays beam in what way? Increased beam hardening
An aluminum filter: Decreases the intensity of all energies of the x-ray beam
"If patient thickness is 6 HVLs, what is the approximate intensity at the midline of the patient? " 12%
A diagnostic x-ray beam has an HVL of approximately 3 cm soft tissue. What percentage of the beam is absorbed by a 21 cm abcomen? Greater than 90
Inherent filtration This results from the glass or metal envelope of the x-ray tube and the window in the x-ray tube housing. It is usually equivalent to approximately 0.5 mm Al.
Added filtration "This is the result of placing an absorber in the path of the x-ray beam. The absorber, usually 1 to 3 mm Al, is positioned between the collimator and the tube housing."
Compensating filter This has nothing to do with patient dose compensating filters are used specifically for shaping the x-ray intensity over the beam receptor is more uniform and results in more uniform optical density.
What are the 3 types of x-ray beam filtration? "Inherent filtration, Added filtration, and Compensating filters"
The inherent friltration in a general-purpose radiographic x-ray tube is usually equivalent to: 0.5 mm Al
"The equivalent added filtration provided by a conventional light-localizing, variable-aperture collimator is closest to: " 1.0 mm Al
The purpose of a wedge filter in diagnostic radiology is to produce: A uniform x-ray beam intensity at the image receptor
The primary purpose of adding filtration to an x-ray beam is to: Remove low-energy electrons
An x-ray beam filter has the greatest effect on dose reduction to the: Skin
X-rays of higher maximum energy can be obtained by doing which of the following? Increasing kVp
"The light-localizing, variable-aperture collimator contributes: " To added filtration
If 5 mm Al filtration is added to the x-ray tube: Optical density will decrease
An x-ray beam can be made harder by increasing: Filtration
"When filtration is added to a normally filtered x-ray beam, the x-ray emission spectrum will: " Decrease in amplitude
Added filtration does what? Protects the patient from unnecesary radiation exposure
Inherent filtration does what? Helps harden the x-ray beam
To produce low inherent filtration in an x-ray beam: A thin section of glass is used
Wedge filters are used to: Obtain uniform optical density
"During mammography, what type filtration is desirable? " Low total filtration
When added filtration is increased: X-ray quality is increased
"If a radiographic tube has 0.5 mm Al inherent filtration and 2.0 mm Al added filtration, adding 1.0 mm Al will do what? " Harden the x-ray beam
"With tube age, inherent filtration will: " Increase
"An x-ray tube has a total filtration of 3.0 mm Al and an HVL of 2.5 mm Al, and emits 180 mR. The addition of 1.0 mm Al will: " Increase the quality of the beam
What is the half-life of Ra 226 ? 1600 yrs
What is the half-life of Cs 137 ? 30 yrs
What is the half-life of Co 60 ? 5.26 yrs
What is the half-life of Au 198 ? 2.7 days
What is the half-life of Ir 192 ? 74 days
What is the half-life of I 125 ? 60 days
What is the half-life of Pd 103 ? 17 days
e- beam qaulity determined @ R50
1 Rad= 100 ergs/gm
1Gy= 1 J/Kg
Hyperfractionation 1-3 more fractions BID 110-140 cGy/ Fraction
Accelerated Fractionation 1-3 completed in a short overall time BID 150-170 cGy/ Fraction
Accelerated Hyperfractionation 1-3 Lots of fraction over short time TID 100-110 cGy/ Fraction
Hypofractionation fewer fx @ a high dose 230 cGy >>
"beta - decay Z , N " "Z+1, N-1"
"Beta + decay Z , N " "Z-1, N+1"
Cs 131 half life 9.7 days
Cs 131 Energy .034 Mev
IORT single fx dose 1000-2000 cGy
mg Equiv to mCi 8.25/exposure rate of nuclide
Bq to mCi Bq/ mCi
mCi to Bq mCi x Bq
Electron d 90 3.2
electron d 80 2.8
pt release F18, I 131 pt release permanent seeds
I 131 therapy dose 100-200 mCi
Pt a dose cGy/hr 50-60 cGy/Hr
LD 50/30 450 rads
LD 50/60 350 rads
Dose to cause progressive cataract 200 rads
SS wipe test results below .005 uCi
SS inventory 3 months
SS wipe tests 6 months
Calibration protocol TG TG 51
QA protocol TG TG40
BSF largest for 0.7mm Cu HVL
1.0 cm of Pb = cm of cerrobend 1.2 cm
penumbra co 60 15 mm
Linac penumbra 8 mm
contralateral breast 200 rad
TBI rx dose 1000-1200 cGy
TBI dose rate 5-10 cGy/min
Gamma knife accuracy 0.5 mm
Linac stereo accuracy 1 mm
x- ray production proportional to KVp kVp2
Thoraceus filter Sn-Cu-Al
Proton Avg Energy 150-250 Mev
BJR 17 requires SSD/ HVL
Jaw transmission 1%
Cerrobend transmission 3.5 - 5%
MLC intraleaf 2%
3.7 x 10^10 = 1Ci
3.7 x 10^7 = 1 mCi
1 dps = 1 Bq
1Ci = disintegration of 1 gram of Ra 226
2.58 x 10^-4 = 1 Roentgen
1 esu/cc air = 1 Roentgen
0.00873 J/kg = 1 Roentgen
0.873 rad = 1 Roentgen
100 erg/gm = 1 rad
100 rad = 1 Gy
1 J/kg = 1 Gy or 1 Sv
rad x QF x modifying factor = Dose equivalent
100 rem = 1 Sv
What is the limit for a RADIATION AREA? 5 mRem IN 1 HR @ 30CM
What is the limit for a HIGH RADIATION AREA? 100 mRem IN 1 HR @ 30CM
What is the limit for a VERY HIGH RADIATION AREA? 500 RADS IN HR @ 100 CM
Created by: Fusty
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