Quiz 2 (PPT 3) Flashcards
Defined as desired modification in the spatial distribution of radiation by insertion of any material in the beam path
Beam modifier
Types of beam modification:
eliminates radiation dose to certain parts of an area where the beam is directed
(Flattening, Compensation, Shielding or Wedge filtration?)
Shielding
Types of beam modification:
Allows normal dose distribution to be applied to the treated area whereas to even out the dose distribution
(Flattening, Compensation, Shielding or Wedge filtration?)
Compensation
Types of beam modification:
Allows for a tilt in the radiation isodose curves
(Flattening, Compensation, Shielding or Wedge filtration?)
Wedge filtration
Types of beam modification:
Where the distribution of the beam is altered by reducing the central exposure area relative to the peripheral
(Flattening, Compensation, Shielding or Wedge filtration?)
Flattening
Review slide 2
Other types of wedges:
Single, centrally located wedge in the head of the linac that is placed within the beam for a fraction of treatment time. The longer the wedge stays in the field the larger the wedge angle
Motorized wedge
Other types of wedges: Uses motion of collimator jaw or leaves during treatment delivery to modify the dose distribution Greater range of wedge angles Less restricted field sizes than solid wedges Time efficient (no need to enter treatment room)
Enhanced dynamic wedge
Other types of wedges:
Uses three dimensional compensation to modulate the dose distribution in a non linear way
Field in field treatment planning technique
MLCs:
Some linacs can have up to ___, ___ or ___ leaves
80, 120, 160
MLCs:
Most leaf thicknesses are ___ or less
1cm
MLCs:
Made of ___ alloy
Tungston
MLCs:
Uses ___ and ___ design
tongue, groove
Some disadvantages of MLC’s include: (4)
No island blocking
Jagged field boundary
Field matching difficult
Penumbra is larger
Cerrobend blocks:
Composed of ? (4)
bismuth, cadmium, lead, tin
BLT w. Cheese
Cerrobend blocks:
Melting point __ degrees F
158
Cerrobend blocks:
Usually created ___ thickness which is equivalent to ___ of Pb and provides ___ of attenuation
7.5cm, 6cm, 5HVL
Cerrobend blocks:
Some advantages over MLC’s include that they are ___ conformal and ___ ___ can be created
more, island blocks
Cerrobend blocks:
Some disadvantages include having to physically lift and ___ blocks in linac for individual fields and having to construct and touch ___ ___
insert, hazardous material
Compensators:
Used initially to address tissue irregularities for sloping surfaces but today can also be used for tissue inhomogeneities ___ the body
inside
Materials can include Pb, aluminum, wax, brass, lucite
Compensators
Can be designed via a CT scan and treatment planning computer
Compensators
Can be used for photon and electron treatments
Compensators
Tissue equivalent material Commonly used materials Paraffin wax Cotton or gauze soaked in water Superflab elastic gel Used to bring dose to surface (build up) Made in various thicknesses 3mm, 5mm, 1cm, 1.5cm
Bolus
Skin dose:
As beam angle of incidence increases skin dose ___
increases
Skin dose:
As field size increases, skin dose ___
increases
Hinge Angle = 180 - (__ x __)
2 x Wedge Angle
