TELETHERAPY Flashcards
These are the most crucial part of radiation therapy treatment
- Px positioning & immobilization
Give 5 CHAR. OF A GOOD IMMOBILIZATION DEVICE
- Ease of use
- Ease of making the device
- Comfort for the patient
- Minimal space requirement for storage
- Resistance to bending & stretching
- Minimal perturbation of beam to not produce artifacts in image acquisition
- Materials should minimally attenuate the radiation beam
- Most common & is made of rigid plastic that becomes pliable when placed in warm water
AQUAPLAST/THERMOPLASTIC MASK
What is the advantage of using aquaplast?
provides great reproducibility
in daily txs, light weight and easy to
use. It can remold if the patient experiences
swelling or sudden weight loss
- Custom, bean bag type pillows that are placed around the px’s body
- air then vacuumed out of the bag for a custom fit & sealed in order to retain shape.
VAC LOC
- Px positioned in prone as it allows the small bowel to drop below the lateral field to avoid severe side effects
Belly boards
- Reference the radiation beam parameters
to the px’s anatomy
Lasers
- Uses a non-IS x-ray film or fluoroscopic machine
2D CONVENTIONAL RADIATION THERAPY
What are the landmarks used in 2d CRT?
bones
- Uses CT-scan for planning for it allows the tumor & normal organs to be defined in 3D
- Uses computer software to calculate the amount of radiation
3d Conformal radiation therapy
What are the 2 mechanisms that shaped the beam in 3d CRT?
CERROBEND BLOCKS & MLC
- Multiple beams are divided into a grid-like pattern, separating the 1 big beam into numerous smaller “BEAMLETS”
- Allows for the radiation dose to conform more precisely to the 3d shape of the tumor by modulating/controlling the intensity of the radiation beam in multiple small volumes
Intensity Modulated Radiation Therapy
What are the different safety features
- Door safety interlocks
- CCTV camera
- Intercom system
- Warning lights
- EM-off Buttons (couch, gantry stand, modulator, control console)
- Additional EM-off buttons
- Uses high RF electromagnetic waves to accelerate charge particles to high energies in a LINEAR PATH inside a tube-like structured ACCELERATOR WAVEGUIDE
LINAC
What is the resonating cavity frequency of medical LINACs
about 3 BILLION HERTZ (cycles/sec)
What is the common device used with LINAC to treat cancer?
EBRT
What is the process of LINAC?
- Uses microwave tech to accelerate electrons in the WAVEGUIDE, then allows these electrons to collide with a heavy metal target
- As a result of these collision, high energy x-rays are produced from the target
- Where px lays still to receive the radiation tx
TREATMENT COUCH/TABLE
What is the treatment couch/table made of?
carbon fiber
- Gantry rotates on horizontal axis bearings located inside it
DRIVE STAND
Components of drive stand
klystron/magnetron
rf accelerator waveguide
water cooling system
preferred for higher electron energies; greater than 6 MeV
klystron
preferred for lower electron energies; 4-6 MeV
magnetron
electron tube that provides microwave to accelerate the electrons; done by amplifying introduced RF electromagnetic waves
Klystron/Magnetron
- Located inside the drive stand and gantry in conventional LINAC
- Provides thermal stability to the system
WATER COOLING SYSTEM
- Helps direct x-ray/electron beams to the patient’s tumor
GANTRY
Components of gantry
electron gun
accelerator structure
treatment head
- Can be mounted in the gantry HORIZONTALLY FOR HIGH ENERGY single or dual energy machines w/ klytron
accelerator guide
another term for accelerator guide
accelerator structure/ accelerator wave guide
- Changes the direction of the electron beam, downwards toward the patient
BENDING MAGNETS
- Bends the pulsed electron beam towards the target for x-rays/towards the scattering foil for electron treatments
BENDING MAGNETS
- Collision of electrons w/ high-density transmission-type target creates x-rays (photons) forming a forward peaking shaped x-ray beam in the direction of the px’s tumor
TARGET
What is the percentage of the electron’s energy that goes into heat?
94%
after the target, what are the other things the beam pass through?
0.25 stainless steel
10.6 mm Al electron stop
1.0 mm W beam hardener
3.0 mm steel beam hardener
spot size of target?
1mm
- Conical shaped metal absorber that absorbs more FORWARD PEAKING PHOTONS; reduces CENTRAL EXPOSURE RATE relative that near the edge of the beam
BEAM FLATTENING FILTER
What is the beam flattening filter usually made of?
TUNGSTEN, STEEL, LEAD, URANIUM/ALUMINUM, COPPER/BRASS
- Electron beams have pencil-like shape & need to be broadened to clinical useful beams and need to be made uniform.
scattering foils
what is the scattering foil usually made of?
Aluminum or Copper
- Monitor integrated dose, dose rate and field symmetry.
IONIZATION CHAMBERS
- Rad beams are collimated by adjusting the upper & lower collimator jaws
COLLIMATORS
What are jaws made of?
HIGH “Z” like tungsten/lead
- Heavy metal field-shaping devices w/ independent moving mechanisms used to create custom like block to spare normal tissue & direct the rad. dose to the tumor
MULTI-LEAF COLLIMATORS (MLC)
what is the thickness and density of the multi-leaf collimator?
- THICKNESS = 6-7.5 cm; made of a tungsten alloy; density of 17-18.5 g/cm3
- Deg. of conformity bet. the planned field boundary and the boundary created by the MLC depends upon:
Projected leaf width
Shape of target volume
Angle of Collimator rotation
Aims of shielding
Protect critical organs
Avoid unnecessary irradiation to surrounding normal tissue
Matching adjacent fields
Ideal shielding material characteristics
High atomic no.
High density
Easily available
Inexpensive
achieved by placing sheets of lead on the surface directly. This is enough, because of the lower penetrating power of the beam
- kV radiation shielding
What are custom blocks made of?
LIPOWITZ METAL/CERROBEND BLOCKS
melting point of custom blocks
70 deg Celsius
density of custom blocks
9.4g/cm3 at 20 deg Celsius (83% of lead)
- Beam modifying device w/c causes a progressive decrease in intensity across beam
- Degree of tilt depends upon slope of wedge filter.
WEDGE FILTERS
material used for wedge filters
Tungsten, Brass, Lead or Steel
- Usually wedges are mounted at a distance of _______ from the skin surface
15 cm
another term for bolus
BUILD-UP BOLUS
- Tissue equivalent material used to reduce the depth of the maximum dose
BOLUS
ideal bolus characteristic
Same electron density & atomic no.
Pliable to conform to surface
Usual specific gravity is 1.02-1.03
- COMMONLY USED MATERIALS FOR BOLUS
Cotton soaked w/ water
Paraffin wax
- More common approach w/c spares much of small intestine & shields spinal cord and vast majority of the kidneys from half of the beams.
4-field technique
This technique is used for Superior border of pelvic portal should be at the L4-L5 interspace to include the external iliac and hypogastric lymph nodes.
AP PORT FIELD
This technique Limit the dose to Urinary Bladder and Rectum in order to permit max. of intracavitary dose to gross parametrial diseases and microscopic or gross pelvic disease (nodal or tumor extension).
Midline shield/ midline block
This Field allows significant protection of small bowel
Lateral
what is the degree of the gantry rotation
360 degree
This has more side effects than the other
conventional linac
This procedure requires less room shielding requirement
TOMOTHERAPY
What are the 2 beams for conventional linac?
x-ray (6 &15 MV)
electron (6,9,12,15,18,21 MeV)
What is the beam for tomotheraphy
xray 6 MV
whats the rotation of the conventional linac?
gantry rotation: limited to 360 deg
whats the rotation for the tomotherapy
slip ring technology-can rotate continuously
