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Photon MU calculation formulas
Gap calculation formula
Gap=d/2(field length 1/SSD + field length 2/SSD)
use 100 is no SSD
Wedge angle formula
- Tissue air ratio
- is defined as the dose at a given point in a medium to the dose at the same point in air
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
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
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
- Scatter air ratio
- scattered dose at a given point in a medium/ dose in air at same point
- 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
The region of the field where the dose falls of rapidly
Define WEDGE ANGLe
The angle through which an isodose curve is tilted at the central axis at specified depth
S is the symbol for
Separation- the measurement between where the beam enter and exits
2D refers to___- 3D refers to ______, and 4D refers to ____.
- plain radiography films
- respiratory gating
An accurate means of calculating the change in PDD in small fields in which the scatter component is small
Maynoerd F factor
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 ____.
a tumor with a depth of 5 cm would need an electron energy of 15 MeV
Who discovered XRAys and when?
- Wilhelm Conrad Roentgen
- Nov 8, 1895
Who discovered radioactivity?
Who discovered radium And when?
- Marie and Pierre Curie in 1898
- they also discovered Polonium
What is the T1/2 of Cobalt 60?
Cobalt 60 treatment (do/do not) use MUs?
DO NOT- they use time
Who developed the first linac and when
Wilderoe in 1928
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
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
- 6) COLLIMATOR DESIGN
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
Dose rates _____ with field size and vary____ with the ____ of the distance.
Photon and electon isodose curves used in dose calculations on a patient usually require the following corrections
- )irregular surface topography
- 2) oblique incidence
The Dmax for any photon beam energy is REDUCED by_______ and _____.
- 1) large field size
- 2) oblique incidence
A beam spoiler is
a sheet of lucite that decrease Dmax and reduces the intensity of the beam
Treatment fields should always be shaped so that the beam edge crosses ______ to the spinal cord.
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.
To minimize the gap between adjacent fields a _____ can be used.
Half beam block
When an isodose curve e of 22degrees is desired, the isodose charts from an _____ and a _____ wedge can be combined.
In an isocentric treatment technique, it is routine to _____ the dose at ______.
In an ELECTRON beam the _____isodose curve bulges and the _____ isodose curve ______.
When POP 6 MV photon beams are used in a 20 cm thick patient the max dose will occur at the
entrance and exits
When a 4 and 15 MV photon beams are uses the max dose be closer to the
4 MV photon side