midterms Flashcards
(88 cards)
1
Q
Parts of Linear Accelerator
A
wave guide
bending magnet
target
scattering foil
ion chamber
electron gun
magnetron
beam flattening filter
collimators
2
Q
vacuum tube where the electrons are accelerated
A
wave guide
3
Q
Directs the electron beam to the target or scattering foil.
A
Bending Magnet
4
Q
where the electrons interact to produce x-rays
A
target
5
Q
placed along the path of the electron beam to scattered the pencil thin electron beam.
A
scattering foil
6
Q
hollow tube with gas usually air where the process of ionization occurs. It controls and switches off the equipment for an adequate radiation to be used.
A
ion chamber
7
Q
it produces electron to be accelerated
A
electron gun
8
Q
device that produces microwaves. It functions as a high power oscillation generating microwave pulses of several microsecond during and with a repetition rate of several hundred pulses per second.
A
Magnetron
9
Q
placed along the path of the x-ray beam in order to attain homogenous intensity of the X-ray beam in the entire field.
A
Beam Flattening Filter
10
Q
restrict the beam to desired beam size or field size
A
collimators
11
Q
patient is positioned on the table using appropriate treatment accessory devices and the table is raised and rotated under the gantry. The treatment area is determined based upon review of any related diagnostic studies, operative reports, CT scan, X-ray, MRI or isotope studies, palpation of the site and tumor visualization.
A
simulation
12
Q
- a diagnostic x-ray machine mounted on a rotating gantry which provides geometries identical with those found on megavoltage therapy machines.
- can be used in either a radiographic or fluoroscopic mode to provide diagnostic quality images on film or a television I monitor respectively
A
simulator
13
Q
deals with the measurements of the absorbed dose resulting from interaction of ionizing radiation with matter.
A
Radiation Dosimetry
14
Q
total number of particles or photons per unit area of the interacting material
A
Fluence (w)
15
Q
ABSORBED DOSE MEASUREMENT METHODS
A
calorimetry
fricked dosimetry
film dosimetry
ionization method
16
Q
involves the measurement of radiation based on the change in the thermal energy per unit mass of the medium. It is based on the fact that almost all the energy deposited in the medium by the radiation beam eventually appears as heat within the medium.
A
calorimetry
17
Q
For water, 1 Gy produces a temperature rise of ___ Calories/gram which can be measured using a sensitive device called
A
2.4x 10-4
thermistors
18
Q
based on chemical changes caused by radiation.
A
fricked dosimetry
19
Q
The chemical radiation dosimeter most commonly used is ____ in which it is oxidized by radiation into ____
A
Ferrous Sulfate
20
Q
Ferric Ion concentration is measured by absorption spectrometry at
A
224 nm and 304
21
Q
When x-ray film is exposed to ionizing radiation. the exposed siver bromide crystaIs form a latent image. The degree of blackening of the film is proportional to the energy absorbed and is measured by determining the optical density with a densitometer.
A
film dosimetry
22
Q
measurement of radiation energy based on ion pairs produced in a given mass of medium.
A
ionization method
23
Q
used for photon beam
A
thimble chamber
24
Q
used for photon beam
A
farmer chamber
25
used for electron beam
markus chamber
26
when a crystal is irradiated, a very minute fraction of the absorbed energy is stored in the crystal lattice. Some of this energy can be recovered later as visible light if the material is heated.
thermoluminescence dosimetry
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phenomenon of the released of visible photon by thermal means is known as
Thermoluminescence
28
DOSIMETRY PARAMETERS
dose
dose rate
monitor unit
isocenter
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general term used to refer to the effect on a material which is exposed to radiation
dose. Ex. 180cGy
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radiation dose delivered per unit time
dose rate. Ex. 180cGy/min for radioactive materials 180MU/min
31
unit used in linear accelerator to determine the dose. Most linear accelerator is calibrated to 1 MU = 1cGy
monitor unit
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point in space where the x, y and z axis intersect.
isocenter
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MODIFICATION TO THE RADIATION FIELD
bolus
compensator
wedges
blocks
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tissue equivalent material that have electron density, physical density, and atomic number similar to that of tissue or water. It increases the dose to the skin. ex. Paraffin Wax, Gauze soaked in water, "Super- Slab“ , Elastomeric Polymer.
bolus
35
intended to compensate for some topographical deficit. A bolus placed in the tissue deficit of the patient is the simplest way to compensate, but because it diminishes the skin sparing effect, retracted tissue _____ are usually employed.
compensator
36
- generally constructed of brass, steel, or lead and when placed in the beam, they progressively decrease intensity across the field.
- bends the dose distribution at some specified depth.
wedges
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used to shield organs at risk, made of lead or Lipowit's metal (cerrobend) which consists of 13.3% Tin, 50% Bismuth, 26.7% Lead, and 10% Cadmium. The physical density of Lipowit's metal at 20° Celsius is 9.4 8/cm', compared with 11.3g/cm
blocks. TBLC (lipowit's metal)
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FIELD ARRANGEMENT IN EBRT
single field
parallel opposed field
multi-field arrangement
moving technique field
39
is the simplest treatment and the dose distribution in tissue is essentially as represented on an isodose chart for the particular energy and the field used.
single field
40
with single field arrangement, Electron is usually the type of radiation used to treat shallow tumors where a rapid drop in dose beyond the ___ depth of the tumor.
57
41
- pair of fields directed along the same axis from opposite sides of the treatment volume.
- are relatively easy to set-up and to reproduced from day to day.
- 100% isodose line is with in the entire treatment volume.
Parallel opposed fields
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Advantages of Parallel Opposed Field
Simplicity and reproducibility of set-up
Homogenous dose to the tumor
Less chances of geometrical miss
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Disadvantage of Parallel Opposed Field
Excessive dose to normal tissues critical organs above and below tumors
44
use of ___ directed at the target volume requires that the beam entrance and exit of each field be aimed at different angles/segments, thereby reducing the dose to adjacent tissues.
multi-field arrangement
45
most popular multi-field arrangement is the "____", which is often used in the treatment of pelvic malignancies. The technique consists of opposed anterior and posterior fields and opposed right lateral and left lateral field.
box Technique
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technique in which the axis of the rotation of the therapy machine, the isocenter, is positioned in the center of the target volume. The radiation source is moved around the patient through are, often a complete circle. It yields a high dose in the target volume where the dose outside this volume falls off rapidly.
moving field technique
Volumetric Modulated Arc Therapy (VMAT), where moving field arrangement is used
47
IMMOBILIZATION DEVICES
1. ALPHA CRADLE
2. THERMOPLASTIC MASK
3. BREAST BOARD (BREAST STEP)
4. PRO STEP
5. VACUUM BAG
6. HEAD REST
48
- used to make sure the patient stays in the treatment position during the course of treatment
- incapable of movement
immobilization
molds, casts, head rest, and other devices are constructed to reduce set up errors and patient movement during treatment.
49
- most common immobilization device used to treat cancers is
- available in different sizes and shapes.
- rigid in room temperature.
- when it heated in water for temperature ___ degree the
material softens and become malleable.
- when it is wet, it is placed over the patient body and conforms to the contour of the treatment area.
thermoplastic
60 to 65
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advantage of thermoplastic
provide great reproducibility in daily treatment, lightweight and easy to use. Additionally modification can be made to mask if the patient experienced with swelling or weight loss during the course of treatment.
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disadvantage of thermoplastic
Windows cut can not be reused and when old it becomes very soft when activated
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TYPES OF IMMOBILIZATION
* Head & neck immobilization.
* Immobilization in Brain tumors.
* Thorax and Breast immobilization.
* Pelvic and abdominal immobilization.
* Immobilization for the Body extremities.
53
used to pull the shoulders out of the treatment field for the neck.
shoulder retractors, H and N immo
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- plate onto which the head immobilization system is secured is referred to as ____
- usually made of Perspex or carbon fiber
- low z material
base plate
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* For the General brain tumor and whole brain cases the mostly common immobilization device is _____
* Immobilization becomes more complex for radiosurgery, Cyberknife and Gamma Knife procedure because the requirements for positional and numerical accuracy for the dose delivery are ____mm.
the 3 clam Thermoplastic orfit
-+1mm
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* For this type of tumor, patient Head positioned with the chin
* Hyper extended to include the superior extent of maxillary antrum in the anterior field without including the eye.
Maxillary antrum Tumors
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* Head positioned with neck in extreme flexion
* Anterior beam can avoid the dose limiting structures such as the optic chiasm, the retina, and much
of the brain tissue.
Pituitary or small brain Tumors-
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Fixation base plate for H&N: It is usually made of ___ It should be low z material and should attenuate the radiation minimally when the beam passes through it.
perspex or carbon fiber
59
3 common immobilization Devices used when treating the tumors in the chest cavity
* VACLOK.
* BREAST BOARD.
* 2 CALMP OR 4 CLAMP THORACIC MOULD
60
* Consists of light weight plastic mattress filled with radiolucent polystyrene (Styrofoam) beads.
* The air is then vacuumed out of the bag for a custom fit and sealed in order to retain the shape.
* Advantage- Radio translucent, after treatment the bag is recycle and used for other.
VACLOK
61
* used specifically for the treatment of breast cancer
* several adjustable features to allow for the manipulation of patient arms, wrists, head and shoulders.
* patient to be positioned with the chest wall horizontal avoiding angulation of the collimator.
* generally constructed of carbon fiber, thermocol allowing the device to be light weight and durable.
* carbon fiber breast boards have lower attenuation levels, which permit maximum beam penetration.
* takes advantages of gravity to pull the large breast down into better treatment position.
BREAST BOARD
62
- used when the patient is treated in prone position , it is allow the small bowl to drop below the lateral field to avoid severe side effect.
- use of ___ minimizes the average volume of Small bowel that would otherwise be within the lateral field during the standard box field technique treatment.
BELLY BOARD IMMOBILIZATION
63
* Properly maintain patients outer contour during treatment with respect to the iso center.
* Other is related to the variation of internal structures During the daily treatment.
* Immobilization system such as vaclok belly board, and thermoplastic masks are commonly used
PELVIC IMMOBILIZATION
64
popular choice for the hip and pelvic positioning due to the patient comfort and setup reproducibility.
VACLOK
65
- quite challenge for us But with this special thermoplastic solution we can perform it easily.
- system consists of a low density carbon fiber base plate with a leg support, two comfort cushions and dedicated masks. The base plate can be indexed to any couch top on
- 2-pin bars and has multiple holes to offer a maximum of possibilities for positioning and immobilizing both upper and lower extremities.
IMMOBILIZATION FOR EXTREMITIES
66
- helps to maintain the position without strain.
- curvature of the patient cervical spine can be altered by changing the support under the head
- Materials Used: ____
HEAD RESTS &WEDGES
Acrylic / Rubber Polvurethane.
67
two pin is designed for reproducible positioning and stable fixation of the base plate. can be placed at the desired indexing indents the couch and can be locked.
indexing bar
68
* Used to maintain the patient position during pelvis irradiation.
* It avoids patient tilt (Rotational error)
KNEE REST AND FOOT REST
69
* Helps in reproducing the opening of the mouth during the treatment.
* Used to minimize the volume of oral mucosa within the treatment field.
* The patients mouth kept open by inserting a mouth bite made from dental impression material.
ORAL PROSTHESIS OR MOUTH BITE
70
An impression of the patient teeth or gum is made in the soften dental material and within approximately _____ the material becomes hard.
5 minutes
71
* Two-part chemical foaming agents are mixed together, initiating the chemical reaction that causes Polyurethane foam to expand.
* The mixed foaming agent is distributed evenly throughout the body form and sealed inside the polyvinyl bag,
* Patient is positioned in the treatment position on top of a polyvinyl bag as the foaming agent expands 10 to 15 mins and conforms to the patient's body contour
* As the foam rises, technician maneuvers it around the patient.
* Once the foam hardens, the customized device is ready for use.
ALPHA CRADLE
72
* External marks placed on either the patient's skin or the immobilization devices
* For initial laser alignment as a surrogate for internal target anatomy.
* In-room laser system in the simulator suite o Should give coordinates in 3 dimensions.
* Preferably made on the immobilization device as it is more reliable as opposed tothe patient's skin (soft tissue & mobile).
* If on skin, preferably marked on bony landmark for a relatively fixed geometry
* Issues - Motion of soft tissue with relation to immobilization device,
* Marks washing off, Wearing off or migration.
ALIGNMENT MARKS
73
Other accessories used in radiation therapy
- Head rest and wedge
- Indexing bar
- Knee and foot rest
- Oral prosthesis or mouth bite
74
Primary and secondary scattering foil. What is their function?
- Primary diverges the field of beam
- Secondary also diverges it but wider
75
If the machine produces electrons, it is for___ tumors
Superficial
76
measures the amount of photons or electrons in Monitor Units (MU). What part of the linear accelerator is this?
ion chamber
77
If the machine produces photons, it is for ___tumors
deep-seated tumors
78
Carousel turns: target is for the production of photons, scattering foil is for the production of___
electrons
79
MLC stands for_____
Multileaf collimator. It shapes the beam according to the shape of the tumor
80
Sequences of production of photon/electron in linear accelerator
Electron gun
Magnetron
wave guide
Bending magnet
Carousel: Target/Scattering foil
Beam Flattening Filter
Ion chamber
Collimator
81
In simulation, the bed/px table used in CT-simulation must be (same/different) with the one used in radiation therapy.
same
82
1R=______C/kg
2.58x10^-4
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1Bq=____dps
1
84
100MU is ____cGy
100
85
- SIB means
- Technique that allows for delivery of different doses to specific areas during the SAME TREATMENT SESSION
Simultaneous Integrated boost
86
IMRT means
Intensity-modulated radiation therapy. SIB is used in IMRT
87
The most crucial part of rad. Therapy treatment are:
Patient positioning
Immobilization
88
Alpha cradle: Patient is positioned in the treatment position on top of a polyvinyl bag as the foaming agent ____mins and conforms to the patient's body contour. As the foam rises, technician maneuvers it around the patient. Once the foam hardens, the customized device is ready for use.
10-15
