Introduction to Radiotherapy

  • Created by: Stephen
  • Created on: 21-05-17 23:40
What prescription information is required?
Treatment site, Energy, Dose, Number of fractions, Overall treatment time, Prescription site, Dr's signature, Date, Wedges or compensators
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What is skin sparing effect?
mV energies make d-max occur deeper than the skins surface meaning dose to skin is reduced
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What is an Isodose chart?
A map of the dose distribution within the irradiated volume
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What is D-max?
Depth at which the beam will deliver its max dose
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Factors that affect dose & fractionation
Radiobiology, Size of treatment volume, Treatment intent, Modality
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What is FSD?
Focus to skin distance
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Define a monitor unit
1 MU = 1cGy for a 10x10 field size at a specific depth (100 MU = 1Gy)
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What does an isodose plan show
Field sizes, Machine angles, Doses, Beam weighting, Wedges
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What is FID?
Focus to image distance
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What is dose (absorbed dose)?
The energy deposited at a specific point. 1Gy = 1J/kg
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What is the point of D-Max for a 4mV beam?
1.0cm
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Define prone
Lying on front
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What is FAD?
Focus to axis distance
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Factors that affect dose distribution
Depth, Field size, Energy, Inhomogeneities, FSD
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Properties of a 1st generation scanner
Pencil/parallel beam & Translate rotate scanner
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What is the point of D-Max for a 10mV beam?
2.5cm
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Tissue phantom ratio
TPR is defined as the ratio of the dose at a given point in phantom to the dose at the same point at a fixed reference depth
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What is the point of D-Max for a 20mV beam?
3.5cm
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Properties of a 3rd generation scanner
360 degree rotation, rotate rotate scanner
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Tissue air ratio
Ratio of absorbed dose at a given point in tissue to the same point in air
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What is FFD?
Focus to film distance
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Define supine
Lying on back
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Typical prostate fractionation
60Gy in 20#
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What is the point of D-Max for a 6mV beam?
1.5cm
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Properties of a 2nd generation scanner
Fan beam & Translate rotate scanner
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Signal to noise ratio trade off
Thick slices = better signal to noise ratio, lower dose, lower resolution and risk of partial volume effect. Thin slices = Lower signal to noise ratio, increased dose, increased resolution
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Houndsfield unit definition and examples
A measure of the linear attenuation coefficient of each voxel compared to that of water. Water = 0, Bone = 1000, Metal = 2000, Air = -100, Vacuum = -2000
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What is the point of D-Max for a 15mV beam?
3.0cm
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Typical breast fractionation
40Gy in 15#
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What is the point of D-Max for a 25mV beam?
4.0cm
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Typical palliative fractionation
20Gy in 5#
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Typical head and neck fractionation
60Gy in 30#
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Other cards in this set

Card 2

Front

What is skin sparing effect?

Back

mV energies make d-max occur deeper than the skins surface meaning dose to skin is reduced

Card 3

Front

What is an Isodose chart?

Back

Preview of the front of card 3

Card 4

Front

What is D-max?

Back

Preview of the front of card 4

Card 5

Front

Factors that affect dose & fractionation

Back

Preview of the front of card 5
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