H.Quality assurance procedures Flashcards
______systems provides safety for patient, staff, and machine
Interiock
_______interlock : Radiation beam is unable to turn on when the door to the treatment room is open
door interlock
___ are either turned off or not able to turn on when conditions are Unsafe
machines
_______interlocks: Stops motion of the gantry when the head of the gantry or imaging systems are too close to the patient or devices
collisions interlocks
Interlock systems have a “functional” tolerance . This means they
work or do not work
Patient devices like blocks, wedges, cones, and compensators are programmed with a code » An interlock will show if the device code does not match the
code planned for that specific patient
How often is door interlock checked
daily
How often is MV, KV, and CBCT (EPID) Collision interlock checked
daily
How often is laser guard interlock checked
monthly
How often is Electron Applicator interlock checked
Annually
A light turns on when the linear accelerator is on or if a radiation source is
exposed
______ are switches that terminate the radiation beam and shut down the machine
emergency switches
emergency switches are checked
monthly
Laser alignment is a daily check because it can affect
geometric parameters
IMRT laser tolerance
1.5mm
SRS/ SBRT laser tolerance
1 mm
_______ is circulated throughout the linear accelerator to cool internal parts such as the accelerator waveguide, source of microwave power, x-ray target, and bending magnets
cooling water
The temperature of the waveguide should be constant at
40 ± 5 degree C
Compressed air is used to move the target, control the energy switch, and control the locking system on the carrousel
» A common pressure used is
45-50 psi
Sulfur hexafluoride (SF6) is a pressurized gas used to prevent arcing within the waveguide » _____ psi is required
25 to 32 PSI
Electrical and mechanical hazards can occur if the software within the
machine fails
According to the FDA, a ____ hazard can cause death or serious injury
class 1
A ____ injury is a hazard that has little risk of causing serious injury
Class II
Examples of _____ include: radiation overdose or underdose due to a faulty machine, dose outside the radiation field, patient/machine collision, and incorrect beam energy
hazards
_____ systems have their own coordinate systems, but they are calibrated to match treatment coordinate systems
imaging
Imaging » Tolerance for non-SRS/SBRT =
2mm
Imaging » Tolerance for SRS/SBRT =
1mm
Audio and visual systems are safety checks that are checked
daily
At least one audio channel and one video channel must be
functioning to treat
what does functional test mean
Works or does not work
Safety lights are a ___ test
functional
Image quality is important in defining target volumes as well as other organs at risk for treatment planning purposes. Image quality and performance is tested using a
water phantom provided by the manufacturer of the CT sim machhine
Image noise on CT machine should be checke
daily
CT numbers (Hounsfield units) are checked
daily and monthly
In all x-ray tubes, warming up the anode is an important step to prolong the
tube life
For CT scanners Tube warmup should be performed each morning and before a scan if the machine hasn’t been used for
2 hours
Beam output can be measured by devices that have
multiple ion chambers or diodes
Checks beam output on the central
axis and off axis
Linear accelerator output is checked
daily, monthly, and annually for each beam energy
Monthly and annual output tolerance is ± 2 percent for
electron and photon therapy
___________ can have an effect on the ion chambers if they are not sealed because it will affect the density of the air within the chambers
Atmospheric temperature and pressure
Pressure and exposure reading have a
direct relationship
As pressure is increased, the output reading is
increased
As pressure is decreased, the output reading is
decreased
Temperature and exposure reading have an
indirect relationship
As temperature is decreased, the output reading is
increased
As temperature is increased, the output reading is
decreased
A ____ factor must be used for temperature and pressure when calculating and measuring dose output if the ion chambers are not sealed and temperature and pressure vary from specific conditions
correction
The light field represents the _____. so the The light field should be identical to it.
radiation field
A light field Mechanical check with a tolerance of
2 mm or 1% on a side symmetric fields
To verify the calibration of leaf positions, use the _______ test
picket fence test
Field size tolerance is
2mm
The field size indicated on the console must match what is ________. This can be tested by measuring the field on the table with a ruler at isocenter (100 SAD) Test for field sizes ranging from 0 x 0 cm to 40 x 40 cm
projected on the patient
Multileaf collimator performance is verified with
radiographic imaging
Leaf position has a ____ tolerance
1 mm
According to the Task Group 142 Report, picket fence test should be performed weekly on machines that perform ____
IMRT
Non-IMRT machines are also checked monthly, but have a ____ tolerance for leafs
2mm
______ lasers are checked daily
alignment
Lasers must point at and intersect at the
isocenter
Side wall lasers must be
collinear
Laser Tolerance ± ____ for non-IMRT machines
2mm
The _______ Test can be used to verify laser accuracy
Winston-Lutz
Winston-Lutz is more common for machines than perfrom
SRS
Winston-Lutz test has ___ tolerance
2mm
To properly check that the gantry rotation for a patient’s treatment is safe, a test run (dry run) of the gantry movement should be performed prior to treatment to make sure there are
no collisions with the patient, table, or any other devices
Tolerance for gantry and collimator angle is
1 degree
There are limit switches for the gantry to avoid over rotation of the gantry. The gantry cannot rotate
infinitely
Mechanical tolerances for linear measurements are typically ±___
2mm
Tolerances for angles are typically
1 degree
Dosimetric monthly checks for output have tolerances of
2%
____checks are “functional” and either work or don’t
safety
____measurements should be permanently recorded and evaluated frequently
QA
Departmental guidelines should outline the proper steps to take when test results are out of _____
tolerance
