Quiz 1 (PPT2 & 3) Flashcards
IM
Internal Margin
ITV
Internal Target Vol
SM
Setup Margin
TV
Treated Vol
PRV
Planning Organ at Risk Vol
IrV
Irridiated Vol
Visible mass to include lymphadenopathy and metastasis.
GTV
Subclinical malignant disease.
CTV
expanded margin for volume differences (bladder, rectum respiration, swallowing).
IM, internal margin
to include motion (CTV+IM).
ITV, internal target vol
Variation in daily patient positioning.
SM, setup margin
to include all geometric variations (ITV+SM).
PTV
Volume to encompass prescribed dose.
TV, treated vol
Similar to PTV except for OAR’s
PRV, Planning Organ at Risk Vol
Tissue that receives a dose that is considered significant in relation to normal tissue tolerance.
IrV
Isodose levels are modified by changing the ___, ___, ___, ___, etc., to produce a desired dose distribution.
energy
field size
beam arrangements
beam modifiers
Isodose levels are modified by changing the energy, field size, beam arrangements, beam modifiers, etc., to produce a desired dose distribution.
Isodose Distributions
Isodose Level Parameter: Isodose levels are lines that pass-through points of equal dose expressed as a ___ relative to a ___ ___.
%, reference point
Two-dimensional graph showing dose delivered to volumes of interest.
DVH
Physical penumbra= ___ + ___ + ___
Geometric, Transmission, Scatter
the lateral distance between two isodose lines at a specified depth
Penumbra
Penumbra Formula
s(SSD+d-SDD)/SDD
Penumbra Formula:
s=
Source size
Penumbra Formula:
SDD=
MLC, Block distance
Penumbra Formula:
D=
Depth
Effect on Penumbra:
Increase source size
Increase
Effect on Penumbra:
Increase SSD
Increase
Effect on Penumbra:
Increase depth
Increase
Effect on Penumbra:
Increase SDD
Decrease
Collimators produce scatter and ___ (increase/decrease?) penumbra.
increase
___ ___ contribute to penumbra due to partial transmission through the ___ end
MLC leaves, leaf
Some MLC’s create little penumbra when the leaves are mounted on ___ ___
diverging carriages
___ leaves create constant penumbra with changing field sizes
Rounded
DVH types:
(most often used) graphs the volume(in the Y-axis that receives the corresponding dose or more in the X-axis
Cumulative DVH
DVH types:
graphs the volume of a structure receiving dose within a specified dose interval
Differential DVH
When choosing an energy consider the following: (6)
- Tumor location
- Tumor size
- Surrounding tissues
- Skin sparring
- Depth
- Exit dose
Two considerations when selecting beam arrangements:
OARs
Homogeneous dose within planning target
How to get a homogeneous dose?
more beams
Beam arrangements that are asymmetric usually require ___ or ___ to be homogenous
wedges, compensators
Field Shape:
Cerrobend blocks have ___ (more/less?) field conformality than MLC’s due to the leaf size
more
Field Shape:
The blocking must always be ___ than the target volume to account for ___
larger, penumbra
Single field advantages: (3)
Simple setup
Uses SSD technique
Decreased treatment time
Single field disadvantages: (2)
Limited treatment depth
Max doses
Parallel opposed fields advantages: (4)
Simple setup
Decreased chance of geometric miss
Homogeneous dose
Ability to weight beams
Parallel opposed fields disadvantages: (2)
Entry and exit doses
Difficult to avoid critical structures
Multiple fields advantages: (3)
Dose conformality
Decreased max dose
Avoidance of critical organs
Multiple fields disadvantages: (2)
More integral dose (total dose in body)
Difficult to avoid critical organs
Rotational therapy: 1, Best suited for \_\_\_, \_\_\_ tumors 2. Able to shape dose distribution based on \_\_\_ of arcs and \_\_\_ of arcs 3. \_\_\_ treatment time 4. \_\_\_ Conformality of doses 5. Varian linacs - type of arc: 6. Elekta linacs - type of arc:
- small, deep-seated
- number, degree
- Decreased
- Increased
- Rapidarc
- VMAT
Partial arc therapy may require “Past-pointing” where the isocenter is placed ___ than the target
deeper
Wedge field technique common uses:
1. Can account for ___ anatomy such as a chestwall or breast
2. ___ a beam such as a in a 3 field rectum
3. Use as tissue ___
4. Use for a ___ ___ target such as a rt sided brain tumor
Wedge/ Hinge angle
180 - 2(wedge angle)= hinge angle
- sloping
- Omit
- compensator
- one sided
Matching fields techniques: (3)
Half beam on central axis
Angling adjacent beams
Match at desired depth (use gap calc)
Matching fields used when: (5)
- Prior treatment to adjacent area
- 3-field head and neck treatment technique
- 3-field breast sclav treatment technique
- Craniospinal
- Mantle
Wedge/ Hinge angle formula:
hinge angle = 180 - 2(wedge angle)
___ ___ advantages:
Simple setup
Uses SSD technique
Decreased treatment time
Single Field
___ ___ disadvantages:
Limited treatment depth
Max doses
Single Field
\_\_\_ \_\_\_ advantages: Simple setup Decreased chance of geometric miss Homogeneous dose Ability to weight beams
POP Fields
___ ___ disadvantages:
Entry and exit doses
Difficult to avoid critical structures
___ ___ advantages:
Dose conformality
Decreased max dose
Avoidance of critical organs
Multiple Fields
___ ___ disadvantages:
More integral dose (total dose in body)
Difficult to avoid critical organs
Multiple Fields
