B. treatment planning parameters Flashcards
Measurements of the treatment field are defined at the
isocenter
The field size is created by two pairs of the
secondary asymmetric collimator jaws
DRRs are a document of the
field parameters
The physical radiation field size is delineated at the
50 Percent isodose line
Tumor depth can be established with
3-D imaging
___of the tumor determines the energy of the beam and the type of treatment
Depth
Superficial tumors are most likely to be treated with
electrons
Deeper tumors are most likely to be treated With
photons
When a treatment is at “midplane” this means the isocenter is located
halfway between the patient separation
if a patient’s separation is 30 cm, then midplane would be at a depth of
15 cm
_____= Distance from the source of radiation to the patient’s skin surface
SSD = source-to-surface distance
If using an isocentric or SAD technique, the SSD will change at
different gantry angles
For _______, the SSD is 100 cm or another specified ‘fixed” SSD
SSD techniques
_____= Distance from the source of radiation to the isocenter
SAD = source-to-axis distance
In current linear accelerators, the SAD is
100 cm
In older Cobalt-60 machines, the SAD was
80 cm
Isocentric technique is when the isocenter is located within the patient meaning The SSD is
less than 100 cm
The secondary collimating jaws are
moveable, asymmetric, and made of tungsten
As field size increases, collimator scatter is ____
increased
The Collimator can rotate ___-degrees, which may be helpful to shape the treatment beam
360
_____ meet at a determined depth within the patient because of beam divergence
Abutting fields
during abutting fields To avoid hot spots, there must be a ___on the skin surface
gap
What is the gap calculation
( L1 / 2 x d / SSD1) + ( L2 / 2 x d / SSD2)
abutting fields are Commonly used in
craniospinal irradiation (CSI)
