Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

TP2 > Beam modelling simplified > Flashcards

Beam modelling simplified Flashcards

1
Q

What is beam commissioning?

A

Adjust a set of parameters to calculate dose distributions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is beam modelling?

A
  • Acquisition of LINAC and TPS profiles by taking into account PDD, Output, Flatness and symmetry
  • Modelled based on CAX distance and beam profiles
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are beam profiles?

A

Measure the relative dose against the corresponding central axis distance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are PDD?

A

Quotient expressed as a percentage of absorbed dose at any depth (Dd) relative to an absorbed dose at a fixed distance (d0)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is profile analysis?

A

Comparision of LINAC and TPS profiles by taking into account field sizes, depth and off axis factors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the impacts of tissue inhomogeneities?

A

Change in absorption of the primary beam and electron fluence.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How can tissue inhomogeneities be corrected?

A

Two methods:
Indirectly-correction method
Directly- inherent to algorithm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are correction methods for contour irregularities?

A

Extended SSDs
TAR or TMR
Isodose shift method

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are correction methods for tissue inhomogeneities?

A

TAR
ETAR
Batho power Law
Effective path lengths

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the TAR method?

A
  • Ratio of dose at a given point in a phantom to the same point in free space.
  • Accounts for the depth of calculation point and field size
  • Adjusts dose beyond inhomogeneity by assuming it causes the same attenuation of the beam equivalent to water (density and thickness)
  • Doesn’t account for scatter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is ETAR?

A

Equivalent TAR accounts for alteration in scatter by caluclating the sum of densitiy in each pixel
(similiar to TAR but longer, more accurate and better for low energies <6MeV)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is Batho Power Law?

A

Applies a correction factor based on electron density of inhomogeneity
-Accounts for incoherent scatter (>10MeV)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the effective path length method?

A
  • Models primary dose variation, best for large distances away from inhomogeneity
  • Compares the water equivalent tissue ability to attenuate the radiation by the same amount of normal tissue.
  • Doesnt take into account scatter, tissue thickness or density
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are some characteristics of lung correction?

A
  • Lower density creates higher dose beyond lung (Build up)
  • Increasing electrons outside the beam reduce side scatter
  • loss of side scatter reduces dose on CAX
  • Significant for small fields and high energy beams (PD dependent on energy)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Effects of bone on entrance?

A

Dose increased to adjacent tissue due to electron backscatter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Effects of bone on exit?

A

Forward scatter of electrons from bone

Build up of electronic equilibrium in soft tissue

17
Q

Other factors of bone?

A

Increased dose on boundary, attenuation and scatter

decreased %DD

18
Q

Effects of air?

A

Decreased Attenuation, dose on boundary and scatter

Increase %Percentage dose

19
Q

What are the pinnacle algorithms?

A

Fast convolve-Fast not used for treatment
Adaptive convolve
CC convolution-Not fast but accurate

20
Q

What are the Monaco algorithms?

A

Monte Carlo-Not fast very accurate
Collapsed Cone algorithms
-Pencil beam-Fast but not good with airgaps

21
Q

What is the CCconvolution-superposition method?

A
  • Calculate primary and scattered radiation separately
  • For each voxel, attenuation factor is calculated and applied to the primary beam
  • A kernel represents the average scatter from the same point is then applied to to each voxel, weighted accordingly to the corresponding amount of primary radiated attenuated at that point
  • Sums primary and scattered radiation to be accurate.
22
Q

What is the Monte carlo method?

A
  • Models the fate of a single photon as they enter the patient or phantom
  • Attenuation and scattering of photons and resulting electrons is taken into account by mapping their paths and calculating an average dose distribution.
23
Q

What is a calculation grid?

A
  • Dose calculated for points throughout the patient model
  • Compromise between resolution and calculation
  • Can alter grid (Coarse to fine)
  • Isodose distributions by joining grid points of equal value and interpolating dose values between them.
24
Q

What does Adaptive convolve do?

A

Speeds up dose calculation by adaptively varying the spatial resolution of the dose grid

25
Q

What does fast convolve do?

A

Uses fewer ray directions or collapsed cones, should not be used for MU calculation

TP2 (5 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions