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Photon MU calculation formulas
- SSD:
- MU=dose/(PDD)(OF)(TF)(WF)
- SAD
- MU=dose/(TMR)(OF)(TF)(WF)
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Gap calculation formula
Gap=d/2(field length 1/SSD + field length 2/SSD)
use 100 is no SSD
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Wedge angle formula
180-hinge angle/2
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TAR definition
- Tissue air ratio
- is defined as the dose at a given point in a medium to the dose at the same point in air
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PDD definition
Percentage depth dose is the absorbed dose at a given depth expressed in a percentage of the absorbed dose at a reference depth at the CAX of the field
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TPR definition
The tissue phantom ratio is defined as the ratio of dose at a specified point in tissue or in a phantom to the dose at the same distance in the beam of a reference depth( usually 5 cm)
Dose in phantom at specified depth/dose at the same distance in a beam
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TMR definition
tissue maximum ratio is defined as the ratio of the dose at a species point in tissue or a phantom to the dose at the same point when it is at the depth if maximum dose
dose in tissue or phatom at specified point/dose at same point at the depth of maximum dose
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SAR definition
- Scatter air ratio
- scattered dose at a given point in a medium/ dose in air at same point
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SMR define
- scatter maximum ratio
- the scattered dose at a specified point in a medium/ the scattered dose at the same point at a depth of maximum dose
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The region of the field where the dose falls of rapidly
Penumbra
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Define WEDGE ANGLe
The angle through which an isodose curve is tilted at the central axis at specified depth
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S is the symbol for
Separation- the measurement between where the beam enter and exits
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2D refers to___- 3D refers to ______, and 4D refers to ____.
- plain radiography films
- CT
- respiratory gating
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An accurate means of calculating the change in PDD in small fields in which the scatter component is small
Maynoerd F factor
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theYet he rule of thumb for selecting electron beam energy is to use the 80% isodose which would me you would multiply the depth by ____.
3
a tumor with a depth of 5 cm would need an electron energy of 15 MeV
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Who discovered XRAys and when?
- Wilhelm Conrad Roentgen
- Nov 8, 1895
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Who discovered radioactivity?
Henri Becquerel
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Who discovered radium And when?
- Marie and Pierre Curie in 1898
- they also discovered Polonium
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What is the T1/2 of Cobalt 60?
5.26 years
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Cobalt 60 treatment (do/do not) use MUs?
DO NOT- they use time
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Who developed the first linac and when
Wilderoe in 1928
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Simulators duplicate the _____ and the _____ of the treatment machine. CT sim can determine the true_____, location, and view the OAR( via _____)
- Geometry, mechanical movements
- volume, contouring
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Dose to a patient depends of sitoe actors:
- 1)DEPTH of calculation point below the surface
- 2)PENETRATING POWER of the beam(ENERGY)
- 3)DENSITY( type of tissue)
- 4) FIELD SIZE
- 5)SSD
- 6) COLLIMATOR DESIGN
- *Do
- People
- Drive
- Family
- Seriously
- Crazy.
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Define dose(aka absorbed dose)
Dose is the energy deposited at a point in a small fixed weight of material surrounding the point in question
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Dose rates _____ with field size and vary____ with the ____ of the distance.
- Increase
- inversely
- square
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Photon and electon isodose curves used in dose calculations on a patient usually require the following corrections
- )irregular surface topography
- 2) oblique incidence
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The Dmax for any photon beam energy is REDUCED by_______ and _____.
- 1) large field size
- 2) oblique incidence
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A beam spoiler is
a sheet of lucite that decrease Dmax and reduces the intensity of the beam
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Treatment fields should always be shaped so that the beam edge crosses ______ to the spinal cord.
perpendicular
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In port films in POP isocentric fields of lung tumor the (AP/PA) film will appear to include a longer segment of the spinal cord.
AP
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To minimize the gap between adjacent fields a _____ can be used.
Half beam block
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When an isodose curve e of 22degrees is desired, the isodose charts from an _____ and a _____ wedge can be combined.
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In an isocentric treatment technique, it is routine to _____ the dose at ______.
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In an ELECTRON beam the _____isodose curve bulges and the _____ isodose curve ______.
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When POP 6 MV photon beams are used in a 20 cm thick patient the max dose will occur at the
______ .
entrance and exits
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When a 4 and 15 MV photon beams are uses the max dose be closer to the
4 MV photon side
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