A.prescription Flashcards
The total dose must be included on the
prescription
on the treatment prescription it must include
- fractionation schedule
- treatment technique
- beam energy
- imaging
- gating
and bolus
some things that aren’t on the prescription are
- MU
- doses to critical structuser
- DVH - dose volume histogram
_____ change depending on the location of the tumor, treatment intent, and the organs at risk surrounding the tumor
Total doses
An example of a typical palliative dose is a daily fraction of
300 cGy for 10 fractions and a total dose of 3,000 cGy
- 5 fractions/week
Total doses range from approximately ____ for curative treatments
50 - 80 Gy (5000 - 8000 cGy)
- 180-200 cGy
To ensure tumor control there are recommended doses to be delivered: For subclinical disease doses of
45 - 50 Gy is recommended
-Subclinical diseases are conditions where the disease is identifiable with laboratory testing or imaging, but have no outward signs or symptoms
The number of fractions and dose per fraction must be
included on the prescription
____breaks up the total dose into multiple smaller doses so that cells can repair
Fractionation
The total amount of fractions varies with the
total tumor dose
___fractionation: Daily fractions of 180 - 200 cGy, five days per week for multiple weeks
Conventional
_______fractionation: Larger dose per fraction with less fractions than conventional fractionation schedules, but same overall dose
Accelerated / hypofractionation
____: Smaller dose per fraction and more fractions than conventional fractionation schedules
Hyperfractionation
Hyperfractionation is recommended for
slower growing tumors
Hypofractionation is recommended for
faster growing tumors
BID means ______
twice daily with 6 hours in between
Beam energy should be displayed on
the prescription
The _____ used for treatments and is chosen depending on the thickness of the patient and the depth of the tumor
beam energy
Tumors in areas of the body that are thicker use ____beam energies
higher
most treatments for pelvic tumors use
15X
most treatments for brain tumors use
6X
When beam energy is increased, skin sparing is increased for
photon beams
Different beam energies have different depths for
dmax
_____particles: Two protons and two neutrons (also known as a helium nuclei) released from an unstable heavy nucleus as it decays
Alpha
Alpha particles has a charge, heavy mass and ___LET
high
____particles: Electrons that are released by a nucleus
Beta
Beta particles are __ charges
Negatively charged (negatron) or positively charged (positron)
____: Electromagnetic radiation, known as photons
X-rays
X-rays have no
mass or charge
X-rays interaction occurs near the
nucleus
_____: Photons naturally emitted from a nucleus
Gamma rays
Natural background radiation include:
Cosmic rays, terrestrial radiation, and radionuclides in the human body
tumor volume that is visible and can be palpated
GTV- gross tumor volume
_______= GTV and the area around it that may have microscopic disease
CTV- clinical target volume
_____= CTV plus motion of the tumor caused by breathing or involuntary motions
ITV- internal target volume
____ are required to determine the ITV
4D CT simulation scans
______= CTV and an area around it to give a margin for uncertainties
PTV- planning target volume
_____ is the volume of tissues that is given a large portion of the dose
Irradiated volume
_____ are organs close to the irradiated area that may affect or limit the dosage delivered
Organs at risk (OAR)
_______ are established based on tolerence doses of the organs at risk and the dose distributions
Treatment fields
Multiple treatment fields are more commonly used for
curative treatment
Single fields are more cornmeniy used for
palliative treatments
____ is arranged depending on the orientation and organs at risk near the tumor
Field orientation
MLCs and other beam modifiers can be used to
further shape the beam
_____dose distributions usually require multiple field
Adequate
_____ fields are usually used for a posterior spine field
Single
_____have a hinge angle of 180 degrees
Parallel opposed portals (POP)
Hinge angle refers to the degrees between each
gantry angle
____ technique is commonly used for structures within the abdomen, such as the pancreas, bladder, rectum, etc.
Three-field
When an odd number of fields are used, it is common for ____to be used to even out dose distribution
wedges
________ is commonly used for deep tumors within the pelvis or abdomen
Four-field technique/four-field box
4-field box fields have a hinge angle of
90 degrees
______ technique has a hinge angle that is less than 180 degrees between two fields
Wedge-pair
- used for small superficial tumors
Wedge-pair- requires wedges to have a more even
dose distribution
The thick ends of the wedges, also known as the _____ face each other
heel,
_______ are also known as “arc therapy,” where the radiation is delivered while the gantry is moving in an arc from one set point to another
Rotational fields
For partial arcs, or arcs less than 360 degrees, the treatment planning method is called
past pointing
For arcs that are ____ degrees, the beam is set to treat at the exact depth of the center of the tumor
360
Arc speed is calculated as
degree/MU
Before treating with an arc, the therapist should do a dry run of the gantry rotation to ensure there will be
no collisions between the gantry and the patient or table
For ____fields, the gantry does not move while the radiation beam is delivered
fixed
different ____ can deliver different percentages of the total dose
fields
AP:PA weighted is ___ proportionally
2:1
AP field will deliver 2/3 of the dose which means to multiply the total prescription dose by __________ to find the amount of cGy delivered in the AP field
2/3
The isocenter is located at __Cm
100
Max field size = ____ cm at 100 SSD
40 x 40
Photon therapy energies range from about
4 to 35 MV
Electron therapy energies range from about
4 to 22 MeV
Treatment table can hold up to
350 pounds
Any changes in the plan must be ____prior to the patient’s next treatment
recognized
If the changes to treatment plan include the field size or shape, the new field must be
imaged for confirmation
Changes in fractionation or dose must be properly documented and followed as
prescribed
Beam ______ will be placed in between the beam and the patient
modifiers
Beam Modifers attenuate some of the primary beam and require an increase in monitor units to compensate for the
partial loss of useful beam
What treatment modifier need to be on prescription
bolus
What treatment modifier does not need to be on prescription
MLC shape, blocks, wedges
