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380 TEST > test 9/30 > Flashcards

test 9/30 Flashcards

1
Q

Skin:

A

KvP Exposure is limited by Skin.
-Depth first 5mm.
- Higher energy Doses MV spare skin.
-Fractionations effect biological dose.

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2
Q

Exposure =

A

Amount of ionization in Air.
-Limitation 3MeV
- Mass charge per/mass of air.
- photons only

  • X = Sum of charge / mass of air collected in.
    X = Q/m
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3
Q

Exposure Units

A

R - roentgen.
SI - Coulomb /kg of air
-1R = 2.58x10^-4/kg of air.

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4
Q

Exposure steps in free air chamber

A
  1. Photons pass through Air & give off Electrons.
  2. The electrons ionize.
  3. Voltage is applied + - .
  4. The charge then creates a current for reading by the electrometer.
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5
Q

D-max & equalibrium

A

D-max = scatter in meets scatter out.

Higher energy = deeper D-max.

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6
Q

Fluence

A

total number of particles entering a sphere of small cross sectional area.

  • How many particles passing through and area.
  • Fluence is maxed out @surface & declines as depth increases.
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7
Q

KERMA

A

Kinetic-Energy-Released per unit Mass in a medium.

Unit= J/Kg. - 1j/kg=1Gy

KERMA = greatest at surface / shallow depth.

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8
Q

Absorbed Dose formula

A

D = Eab/m

(Eab = total energy absorbed in mass of material.

R Roentgen (air) > RAD (body) > REM (limits of structures)

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9
Q

Quantities = Absorbed dose

A

photons - Kerma liberate charged particles - Dose - local energy deposit.

  • Most damage from indirect - KERMA = forward moving energy = hasn’t reached back scatter yet.
    -kerma = different then depth dose.
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10
Q

dose build & skin sparing

A

Old machines = limited by skin dose.

MV beams = skin sparing = forward moving energy = penetrates deeper then lower energy beams.

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11
Q

Skin sparing

A

Photon beam

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12
Q

D-max =

A

max dose as a % of beam attenuation.

  • scatter in scatter out.
    -electron equilibrium here.

-As photons move into a medium, they set electrons in motion
Electrons then deposit dose along their tracks

  • Increase energy = increased DMAX depth.
  • Surface dose (before Dmax) occurs from backscatter electrons & contamination.
  • increased energy = Dmax
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13
Q
A
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14
Q

Mean energy to produce iron pair:

A

33.97eV/ion pair

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15
Q

1 R = .876 RAD IN AIR.

A

Used in converting R to RAD
dose in air - rad

Fmed = (.876) x (medium / air)

convert exposure to radiation dose , once you have (X)exposure

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16
Q

Dose in medium formula.

Convert chamber reading to exposure;

A

X = M (Nx) (Ctp) (Pst) (Pion)

X -exposure.

M- electrometer reading (from clinic).

Nx - calibration reading ( from lab).

Ctp - temp pressure correction.

Pst - Stem leakage.

Pion - ion recombination.

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17
Q

Fmed

A

If you take the exposure and multiply it by the FMED, you get the dose in the medium

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18
Q

Temp pressure effect on the ion reading

A
  • Cold air is more dense = higher reading.
  • Higher temp = more pressure = lower reading.
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19
Q

Farmer chamber

A
  • 300v
  • 0.1cGy
  • 1-2% loss charge w/ recombination.
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20
Q

Dose in free space =

A

Measuring in an ION chamber (w/o water) free of obstruction.

-Dose in Free Space (Dfs): dose deliver @ center of a sphere of a medium which is just large enough to have electronic equilibrium at its center

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21
Q

Goal of dosimetry is to compute energy deposition in matter

A
  • Monte Carlo Algorithm –
  • most accurate method
  • “gold standard.
  • Tracks a particle history for each interaction.
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21
Q
  • Amount of ionization in air is dependent upon photon energy
  • Increase energy = Increase ionization rate
A
  • Ionization Chamber – collects the charge
  • Electrometer - measures the charge
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22
Q

LET – linear energy transfer

A
  • larger mass & charge transfer energy easier.
  • Alpha deposit all energy.
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23
Q

Measurement instruments categorized into type

A
  • Radiation machine calibration
  • Survey work
  • Personnel monitoring
  • In vivo patient measurements
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24
Q

Survey work instruments =

A
  • Verify tray source.
  • Sensitive but not accurate. enviroment
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25
Q

Radiation machine calibration =

A
  • Data comparison to annual calibration.
  • Very accurate, not sensitive.
  • Acceptance test = after installation.
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26
Q

Personal Monitoring

A
  • track workers.
  • Needs to be sensitive = measures small amounts.
  • Cumulative exposure.

OSL

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27
Q

In VIVO patient measurements

A
  • monitors PT during Tx.
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28
Q

3 Categories of radiation detectors, according to medium.

A

1) GAS Ionization.

2) Solid State.

3) liquid

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29
Q

Gas Ionization Detectors:

A
  • Ion chambers
  • proportional counters.
  • GM survey meters

(they air open AIR)

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30
Q

Solid state detectors :

A
  • TLD, Film, Diodes, MOSETS, polymer gel, Scintillation ( survey meter).
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31
Q

Liquid Dosimeters:

A

Calorimeters ( Standarization lab)

Chemical

(very rare to use)

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32
Q

Phantom types

A

1) Geometric : virtual (epoxy slabs), Water tank (annual calibration),

2) Anthropomorphic – designed to mimic shape of (average) patient.

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33
Q

Gas ionization chambers -Detectors

A
  • How we get exposure (X)
  • Measured w/ electrometer.
  • Ions attracted to opposite charged electrodes.
  • High temp = air expands = lower air density = lower readings.
  • Cold air = dense air = higher readings.
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34
Q

used mainly in National Standards Labs (NIST)

A
  • Gas Ionization Detectors Free – Air Ion Chamber.
  • X-rays enter camber & ionize along beam path.
  • The standard of measurement.
  • Primary gold standard = sent to lab for calibration.
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35
Q

GAs ionizing detectors free- Cavity ion chamber

A
  • Air cavity w/ air shell that surrounds.
  • entire cavity irradiated.
  • shell + cap = proper build up 5mm.
  • thickness of cap and chamber wall 5mm
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36
Q

Provides ability to measure dose @ Dmax:

A

Free air cavity.

  • X = M * Nx * the 3 correction factors .
  • Air cavity of mass
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37
Q

Gas Ionization Detectors Free- The 3 types of Cavity Ion chambers

A

1) Thimble chambers = Farmer, mini.

2) Flat cavity chambers = plane parallel.

3) Well ion chambers
= Test radioactive sources. Brachy source calibration

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38
Q

Farmer Chambers

A
  • thimble.
  • exclusive photon calibration in RT.
  • calibrated every 2 years.
  • Inner wall serves as electrode.
  • volume 0.1 to 1.0cm^3
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39
Q

Thimble chamber / farmer

A

Insulator , thimble wall, to electrometer, central electrode.

-

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40
Q

Plane parallel ion chamber

A

Pancake chamber.

  • Changing depth interferes.
  • Strength = measuring dose at shallow depth / at wild up region
  • collection diameter 5mm - high spatial res in beam direction
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41
Q
A
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42
Q

Plane parallel ion chamber

A

Lieanear accelerator = has 2 parallel ionization chambers.

  • to double check for in case of failure.
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43
Q

Gas free cavity - Extrapolation chamber

A

extrapolation = using tarting point to estimate values outside of given range.

  • Good for measuring SURFACE DOSE.

extrapolating to ZERO = SURFACE dose .

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44
Q

Correction for temp & pressure:

A

Ctp=
(760/p) = (273+T/295)

22c is standard temp.

760mmHg standard pressure.

correction factor are unit-less.

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45
Q

F to C formula

A

C = (F - 32) *5/9

46
Q

C to F formula

A

F = (C * 9/5) +32

47
Q

electrodes in well guarded ion chamber:

A

1) central / collector -1mm AL rod.

2) Guard electrode 2-purposed: prevent leak & define vol.

3) Thimble wall - ground potential & kept same as collector electrode (300V)

48
Q

4 variations within Free Air chamber

A

1) Air attenuation.

2) Recombination of ions - when a +&- cancel out.

3) temp, pressure, Humidity.

4) Ionization produced by scatter photons.

49
Q

Free Air chamber - Stem Effect/ Stem Leakage:

A
  • 1-10%
  • Increase energy = increased stem effect.
  • corrects for falsely created charges collected
50
Q

Ion recombination :

A

A loss of charge occurs from + -

1-2% loss id charge is seen

51
Q

GM counter

A

range of 0.01mR/h to 1.0R/h

Very sensitive not accurate

52
Q

Solid State
TLD

A
  • Used in vivo, phantom, personal.

-Crystal storage.

  • heated, releases light = to RAD.
  • 300-400cGy
  • lithium fluoride Z 8.2.

glow curve

53
Q

Annealing

A

Heated to release residual signs and condition sensitity.

400 at 1 hour before.

54
Q

TLD pros & cons

A

Pro: small, reusability, wide range .001-1000cGy, tissue equivalence, no wire.

CON: not instant, only be read once

55
Q

FILM

A

Degree of film blackening related to absorbed dose.

  • PRO: spatial resolution, smaller crystals, permeant record, inexpensive.

-CON: developing, sensitive to light, strong photon energy dependance.

  • OD optical density = measure of light attenuated by film.
56
Q

Radiochromic film

A
  • not based on silver halide, rather monomer.
  • sensitive to all energies,, self developing.
  • CON: ingestive to light - hight energy needed 10-50Gy
  • expensive
57
Q

Diodes solid state

A
  • AC TO DC
  • ELECTROSTATIC
  • in vivo skin sensitive.
  • daily QA
  • instant readouts

con - connected to wire.

57
Q

MOSFET

A

Measures threshold voltage shift which is proportional to radiation dose

  • pro - reusable, instant read.
  • con- limited lifetime
58
Q

Liquid Dosimeters - Calorimeters

A

– insulated container used to measure small amount of heat energy

  • direct absorbed dose measurement.
  • Functions as absolute dosimeter for measuring absorbed dose.

Only found in standards laboratories.

All energy absorbed in a material by radiation appears as heat
Used to calibrate ion chambers

59
Q

Liquid - Chemical

A

Fricke dosimeter.

  • not common RT.
  • Color change measured with spectrophotometer

-

60
Q

Ideal Chamber Characteristics

A
  • minimal variations in: Sensitivity or exposure calibration over wide energy range.
  • minimal stem leakage.
  • minimal ion recombination losses.
61
Q

to convert chamber reading to exposure we use ?

A

X = M (Nx)(Ctp)(Pst)(Pion)

62
Q

R to RAD

A

(X)(Fmed)

Fmed= 0.876 * medium/Air

63
Q

REM conversion

A

RAD * QF

64
Q

Teletherapy –

A

radiation delivered with an external beam

65
Q

Two types of accelerators

A
  • Linear accelerators:

accelerate charged particles in straight line.

  • Circular accelerators:

microtrons, cyclotrons, synchrotrons & betatrons

66
Q

electron linear accelerator

A

Accelerated with microwaves.

Electron beam can treat patients, or it can hit a target to produce photons

Collimation determines beam size

Has 2 photon energies and 5-6 electron beam energies

67
Q

SAD – source to axis distance

-non-adjustableiso

  • iso always 100cm
A

SSD – source to skin distance.

  • All fields have an SSD.
  • SSD changes as the gantry angle changes
68
Q

Couch

A
  • Mylar top.
  • 6 degree of freedom.
  • orthogonal 90 degrees.
  • low z.
69
Q

Electron gun:

A

Source of electrons.

  • Beam width 3mm
  • SF6 gas housed, to reduce arcing.
  • primary collimator max FS 40x40.
  • Secondary XY jaws.
70
Q

Electron beam energy:

Photon beam energy:

A

electron: 6MV Mono

Photon: 0-6MeV, AVG 1/3max = 2MeV Poly

71
Q

Linear Accelerators - Waveguide:

A

Evacuated copper pipe - electrons are accelerated.

2 types of microwaves used.

v=3000MHz pulsed radiation

72
Q

Traveling Wave

A

has circulator: prevents microwaves from reflecting back

73
Q

2 high power microwave devices ;

A

1) Magnetron. - produce own microwaves - lower energy linac.

2) Klystron. - Amplifies, more stable, expensive, high power, RF source needed.

74
Q

Magnatron

A

cheaper

Own low power microwaves

Electrons exposed to mag field.

auto generates

75
Q

Klystron

A

Higher power 8MW

requires RF driver

More stable.

more expensive

Amplifies

76
Q

Power in put power output

A

1) micro power to waveguide in pulses.

2) power supply DC to modulator.

3) high power pulses to klystron or magnetron & electron gun.

4) Gun injects pulsed electrons to waveguide.

5) Electrons accelerate down waveguide in 3mm beam.

77
Q

Modulator:

A

Controls pulses to microwave

  • power regulator = PFN pulse forming network = sets the dose rate === helps have patient on the table shortest amout of time.
78
Q

Treatment Head Function:

A

to shield leakage & house major components

79
Q

Treatment Head components

A

1) X-ray target; photon mode only

2) Scattering foil; electron mode only

3) Flattening filter; photon mode only

4) Monitor ion chamber (2x)

5)Fixed (primary) & moveable (adjustable) collimators

6) Field defining light

7) Optical Distance
Indicator (ODI)

80
Q

photon Beam - treatment head path :

A

1) Electron beam
2) X-ray target.
3) Primary.
4) Carousel.
5) Flattening.
6) Ion Chamber.
7) Secondary.
8) Mount locks

81
Q

Electron Beam - Treatment head path

A

1) Electron beam.
2) Primary.
3) Carousel.
4) Scattering Foil.
5) Ion Chamber.
6) Secondary.
7) Mount locks.
8) Cone applicator.

82
Q

Flattening Filter

A

as high energy beams are more forward peaked, a flattening filter which is thicker in middle attenuates more than the edges

  • Makes intensity uniform across the beam
83
Q

X-ray mode

A

transmission target used for Photon mode.

84
Q

Flattening filter characteristics

A

mixed metal = uranium, AL, tungsten.

Attenuates the High energy photons from the forward peaked photon beam .

Reduces dose rate 4x (24Gy to 6Gy/min)

Makes beam profile more uniform.

SRT faster w/ removed

Diffrent fillter for diff energy

flat in terms of quantity

85
Q

Flatness

A

Quantity

all points equal within 3% at 10cm depth.

  • Only account for the central 80% edge penumbra
  • 20% fall off from lateral sides
  • past 10cm depth the profile is higher at central axis.
  • Overcopensates at the surface, making lateral horns.
86
Q

FFF

A

Flattening Filter Free

higher dose rates w/ 10x energy it is 4x higher - treat in 1/4 the time

87
Q

Symmetry Vs Flatness

A

Symmetry – 2%

A pair of points equidistant from the CA must be within 2%

10x10FS

Flatness – 3%

Variation of dose in comparison to the CA dose (80% of field) at a depth of 10cm

88
Q

MU

A

Monitoring Units :

Amount of time to deliver 1cGy, w/ 10x10FS to 10cm Dmax @100cm away

89
Q

Monitor Ion Chamber 3 purposes

A

1) feedback to maintain dose rate.

2) track total dose Mu delivered.

3) Measure flatness & symmetry.

90
Q

Primary collimators

A

fixed at max FS 40x40 @100cm

91
Q

secondary collimators

A

movable

tungstan .5%

Aysymmetric jaw abillity

transmission penumbra avoided w/ jaws

92
Q

electron mode

A

Target removed & scattering filter used

thin foil high Z to scatter electron beam , not to cause brems

93
Q

Applicator

A

cone used with electron mode , can’t used w/o it .

interlocks prevent use w/o it

start at 6x6

94
Q

Bend Magnets

A

change direction of horizontal to vertical

linac 270 instead of 90

95
Q

Co 60 teletherpy unit

A

first particle MV therapy unit

very reliable , same decay rate

Co-60 half-life: 5.26 years; lose 1% of activity per month

96
Q

Photon beam charteristic

A

Field Divergence – the radiation beam spreads with increased distance from the source

97
Q

Annual QA measuring across central axis water tank

A
98
Q

Penumbra – edge of the field that doesn’t receive the whole treatment dose

A

Geometric penumbra: non-point source

Transmission Penumbra: collimator or jaw transmission

Scattering of photons & secondary electrons

99
Q

P = s (SSD + d -SDD) / SDD

A

Electrons always have larger / wider penumbra = they scatter more.

electron penumbra bulge and scatter laterally.

100
Q

Grenz Ray therapy

A

20Kv

101
Q

Contact Therapy

A

40-50Kv

2mA @2cm

102
Q

Superficial therapy

A

50-150Kv

103
Q

Orthovoltage

A

150-500Kv

104
Q

Supervoltage

A

500-1000Kv

105
Q

G C S O S

A

20,

40-50,

50-150,

150-500,

500-1000

106
Q

Van de Graff

A

early treatment machine

107
Q

Betatron

A

doughnut

6-40MeV

108
Q

Microtron

A

Circular w/ linac head

109
Q

tomotherapy

A

rotating

no flat filter no FS limitation single energy

110
Q

Cyclotron

A

protons

particle accelerator

proton spread out Bragg peak

111
Q
A

380 TEST (1 decks)

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