First Year Exam: QA Flashcards
1
Q
What is the daily QA output dose tolerance?
A
3%
2
Q
In simple words, what is the purpose of Daily QA?
A
To check output and watch for trends in parameters
3
Q
True or false
For photon energy tracking in daily QA, you are measuring absolute energy.
A
False
You are tracking relative change since baselines
4
Q
How does a device like daily QA calculate output?
A
It has a central axis ion chamber which is corrected for temperature and pressure
A background collection is taken and subtracted out
You apply an array calibration which was first taken at time of output adjustment, when you were confident that delivered dose was exactly what you know
You measure relative to your baseline output (which you would’ve taken when everything was 1.000)
5
Q
True or false
For electron energy tracking in daily QA, you are measuring absolute energy.
A
True
6
Q
How setup is used by DQA3 to calculate electron energy?
A
5 ion chambers around the board, each with different buildup materials, thicknesses, and different depth dose
7
Q
What is the accuracy of electron energy calculations?
A
4-6 MeV: within 2% accuracy
6-20 MeV: within 1% accuracy
8
Q
What mechanical tests do you do for morning QA? What are their TG-142 recommended tolerances (assuming SRS/SBRT machine type)?
A
Laser localization: 1 mm
ODI: 2 mm at ISO
Collimator size indicator: 1 mm
9
Q
What safety checks do you do on Linac for Daily QA?
A
Audio and Visual Door interlock Beam off interlock Beam on light indicators Collision interlocks
10
Q
What imaging tests do you do daily? What are the tolerances?
A
Positioning/repositioning (IGRT) accuracy: 1 mm
Isocal (for SRS machine only really): 0.035, 0.05, etc
MV and kV alignment: 1 mm
Collision interlocks: (pass or fail)
11
Q
What does Winston Lutz tell you about your machine?
A
Size of isocenter
12
Q
What is the Winston Lutz test actually testing?
A
Coincidence of the radiation and mechanical isocenter
And for us specifically, also imaging isocenter since we use CBCT to setup the cube. But if you used lasers and no fine tuning with imaging, then you wouldn’t be using imaging isocenter
13
Q
What are the tolerances for the WL test?
A
0.5 mm mean deviation
1 mm max deviation
14
Q
How does doselab pro calculate result for winston lutz?
A
- First figures out the edge of the radiation field by finding the 50% threshold
- Then determines the center of each field
- Then locate sthe center of the ball using image thresholding as well
- Then the deltas are determined for x and y direction separately
- Total delta is then just distance formula
15
Q
What does MPC check?
A
Geometric accuracy using just 6X
output for all energies
16
Q
What is the tolerance for the picket fence test (assume SRS machine)
A
Technically, according to TG-142, it’s just visual inspection
But we use 0.5 mm max deviation since we quantitatively measure
17
Q
What MLC tests are TG-142 recommended for monthly QA? What are the tolerances?
A
Pattern test, atleast 2 patterns: 2 mm
Travel speed: < 0.5 cm/s deviation from max
Picket Fence: 1 mm
18
Q
What MLC tests are TG-142 recommended for annual QA?
A
Transmission
Picket Fence
Spoke shot
Coincidence of light and x-ray field
Segmental IMRT (step and shoot) test or moving window (IMRT) test for four cardinal gantry angles
19
Q
What images are taken in isocal?
A
4 MV images at different collimator rotations
MVCT images
kVCT images
20
Q
What is the purpose of isocal calibration?
A
To fine-tune imager alignment so that imagers are exactly centered to radiation isocenter with respect to gantry angle
The calibration calculates the needed longitudinal and lateral corrections of both MV and kV images at each angle, to make this happen
The angle-by-angle corrections are saved to the system and applied to all imaging thereafter
21
Q
What is the tolerance for a monthly TG-51 output constancy check?
A
2%
22
Q
What is the tolerance for a monthly profile constancy check?
A
1%
23
Q
What is the R50 monthly tolerance?
A
2mm
24
Q
What is the pdd(10) monthly tolerance?
A
2%
25
What does beam profile constancy mean?
Making sure your current profile is consistent with your baseline profile
26
What is the annual TG-51 output calibration tolerance for x-ray and electrons?
+-1%
27
What are some mechanical TG-142 monthly tests?
```
Light vs Radiation Field
Jaw positioning accuracy
ODI vs Front Pointer
Laser localization
Gantry/Collimator angle accuracy
Accessory functionality
Crosshair centering (walkout)
Couch position shifts
```
28
What is the tolerance for Light vs Radiation Field?
2 mm symmetric (or 1%) on a side
| 1 mm asymmetric (or 1%) on a side
29
What is the tolerance for Jaw Positioning accuracy?
2 mm symmetric
| 1 mm assymmetric
30
Tolerance for ODI vs front pointer
1 mm at isocenter
31
Tolerance for monthly ODI vs front pointer
1 mm at isocenter
32
Tolerance for monthly laser localization
< 1 mm
33
Tolerance for monthly gantry/collimator angle accuracy
1 degree
34
Tolerance for monthly accessory functionality
pass/fail
35
Tolerance for monthly crosshair centering (walkout)
1 mm
36
Tolerance for monthly couch positioning (SRS machine)
1 mm / 0.5 degrees
37
What safety tests are recommended for monthly according to TG-142?
Laser Guard functionality
38
What OSMS/Calypso tests are recommended monthly by TG-142?
Output constancy
Phase/Amplitude beam control (magnitude and localization pretty much)
In-room respiratory monitoring
Gating interlock
39
What are the TG-142 recommended imaging tests for kV and MV, and their tolerances?
```
Imaging and treatment coordinate coincidence - < 1 mm (this is pretty much what we do for daily QA)
Scaling - < 1 mm
Spatial resolution - baseline
Contrast - baseline
Uniformity - baseline
Noise - baseline
```
40
What are the TG-142 recommended imaging tests for Cone-Beam, and their tolerances?
```
Geometric distortion - < 1 mm
Spatial resolution - baseline
Contrast - baseline
HU constancy - baseline
Uniformity - baseline
Noise - baseline
```
41
What does array calibration, in general, spit out?
The relative sensitivity differences between detectors in an array. The actual calibration spits out individual correction factors for each detector
42
What does dose calibration, in general for arrays, spit out?
A single value that converts relative dose values to absolute dose values
43
True or False
Array calibrations are energy and accelerator specific?
False
Array calibrations are all relative, so the machine that it's done on is not important
44
True or False
Dose calibrations are energy and accelerator specific?
True for both!
But for us, since all three machines are matched, we use the same dose calibrations for each machine.
45
What does background measurements actually measure?
Leakage current of each individual detector. This calculates the background rate
46
What is the spacing and density of diodes in an arccheck?
Spacing: 10 mm
Density: Sub mm due to helical arrangement (diagonal short cut and entrance and exit overlapping)
47
How does the arccheck software figure out gantry angle without using an RT Plan?
By calculating the timer interval between entrance and exit dose
48
True or False
ArcCheck interpolates
False
It only uses the measured data points for it's gamma analysis. The dose map and interpolations in between measurement points are just for show.
49
What is the approximate maximum angular dependence that an arccheck diode may feel?
8% at 90 deg incidence
50
What is the effective diameter of arrays in an arccheck (with and without divergence)
22 cm (21 without divergence)
51
What is approximate 9 month reproducibility of ArcCheck?
+- 0.2%
Just remember: it doesn't change that much, but it does change a bit since it's diodes
52
What dependencies do the diode detectors have on an ArcCheck?
Temperature and Energy
53
How many detectors in a MapCheck?
1527
54
What is the diagonal spacing and row offsets of the detectors in a MapCheck?
Diag: 7.07 mm
| Row Offset: 5 mm
55
What is one thing about a Tomo verification plan for IMRT QA that you need to know about ahead of time?
Number of fractions
Because you need to divide the verification plan dose by that number
56
What is the Lucy Phantom made out of?
Lucite
57
What film do we use for SRS QA? Why?
EBT-XD
It has a large dynamic range (0.4 - 40 Gy)
58
True or False
EBT-XD exhibits significant energy dependence in the MV range?
False
Minimal
59
Why do we like to use film for SRS QA?
1. It's near tissue equivalent
2. it has excellent spatial resolution (5 micrometers)
3. Excellent uniformity
4. Minimal UV/light sensitivity
60
Briefly describe the lateral scan effect
The color value measured depends on the location of film placement relative to isocenter of scanner.
Film scanned away from center will have lower color pixel values which results in higher measured dose, because the light has to travel greater distance through the film before it bounces back.
61
If you were to use a ion chamber insert for Lucy+Ion Chamber QA of SRS, which would you use and why?
A16 or W1 because you want small detectors for small fields
62
How would you make a verification plan using ion chamber for Lucy and SRS QA?
Make a verificationplan and calculate the average dose to the chamber's collecting volume.
When you take measurements though, you need to take the chamber readings from EACH FIELD separately, so you should probably also calculate verification plans for separate fields
63
How long do you have to wait for dose to saturate for Lucy QA?
At least 4x the time interval between first irradiated film and last irradiated film
64
According to TG-142, what are the recommended Linac QA's to perform weekly?
Trick question
TG-142 doesn't specify a weekly category for anything other than MLC, in which case the weekly recommendation is a PF test
65
According to TG-142, what are the recommended Linac OBI QA's to perform weekly?
Trick question
TG-142 doesn't specify a weekly category for anything other than MLC
66
What is the end goal of all TG-142 tolerances?
Make sure that the error in dose delivery is below the ICRU recommended 5%
67
What daily QA is recommended for non-radiographic motion tracking devices, such as OSMS and Calypso, according to TG-147?
Safety checks (ceiling and wall mounted parts are rigid, fixed, and not obstructed)
Static localization - use target of known geometry
Documentation - recording of daily QA results
Any other vendor recommended tests
68
What monthly QA is recommended for non-radiographic motion tracking devices, such as OSMS and Calypso, according to TG-147?
Safety (same as daily + gating delivery)
Static localization
Dynamic localization accuracy (same as our monthly)
Documentation - Recording of monthly QA results
Any other vendor recommended tests
69
What annual QA is recommended for non-radiographic motion tracking devices, such as OSMS and Calypso, according to TG-147?
Safety - Backup power, batteries, gating, emergency off, etc
System integrity - visual inspection of cameras
Camera stability - no slipping or moving
Positioning and localization accuracy
Gating + tracking
Data transfer
Documentation
70
Which task group gives recommendations on CT Sim QA?
TG-66
71
What are the three major differences between a CT sim vs a regular CT?
Lasers
Flat couch top
Large bore (85 cm)
72
Why does TG-66 recommend NOT having a door interlock?
Because interrupted a scan forces you to redo it, and this would result in more dose to patient. This isn't worth it, especially considering that the dose to anyone entering the room for a brief amount of time would be minimal and well below regulatory limits
Also another added layer of screwing up optimal contras timing
73
What CT Sim tests are recommended to be done daily according to TG-66?
System calibration
Collimator assessment
Spatial integrity
Laser alignment localization
CT Number accuracy (for water)
Image uniformity and noise (visual inspection)
74
How often do you measure CT number accuracy?
Daily for CT number of water only
Monthly for 4 to 5 difference materials
Annually for a electron density phantom
75
Tolerance for daily CT number accuracy
0 +- 5 HU
76
How often do you measure image noise?
Daily
77
In-plane spatial integrity tolerance
1 mm
78
How often do you measure in-plane spatial integrity?
Daily for x or y direction
| Monthly for both directions
79
When do you measure field uniformity and for what kVp settings?
Monthly - most commonly used kVp
| Annually - other used kVp settings
80
What kVp's do we use in our clinic?
140 kVp for everything
81
Why do we only use one kVp setting for all scans?
So we don't need multiple HU maps for eclipse
82
Field uniformity tolerance
Within +- 5 HU
83
When are you supposed to measure spatial and contrast resolution?
Annually, but we do it monthly as well
84
Tolerance for spatial and contrast resolution
Vendor specification +- 1 visible node on catphan
85
How often should you measure CT slice width?
Monthly
86
Frequency of patient dose from CT-scan, CTDI measurement
Annually
87
Frequency of table movement and positioning tests
Monthly
88
Frequency of artifact evaluation
Monthly
89
What are some common CT artifacts?
```
Beam hardening (cupping artifact, streak and dark bands, metal artifacts)
Metal artifacts
Ring artifacts
Motion artifacts
Photon starvation
Partial volume averaging
Truncation artifact
```
90
Bore size of a CT sim
Bore size of a standard CT
CT sim: 85 cm
Standard CT: 70 cm
91
How is slice width measured using a CatPhan?
```
Find the average background HU value
Find max value of the 23 degree tilted wire
Find FWHM value
Set WL to FWHM value and WW to 1
Measure
Multiply by tan23
```
92
What is the morning warmup for TB3, (the SRS machine)?
Bonus points: List them in order
- Arm initialization
- Isocal Verification
- Safety tests (audio, visual, collision paddles, interlocks, beam on indicators)
- OSMS Daily QA
- Light field accuracy using DailyQA3 board
- Constancy using DailyQA3 (output, symmetry, flatness, energy, radiation field size)
- IGRT Accuracy using Winston Lutz cube
- kV-MV coincidence
- Winston Lutz
- Laser localization
- Cone-WL if morning of Cone SRS
- MPC
93
Monthly HU constancy tolerance
Baseline +- 50 HU
94
Describe action level 1
Inspection action
Sudden and significant deviation from expected values that have become normal in your mind from QAing frequently
Values may still be within tolerance, but they should deem inspection if sudden jump
Actions: treatment may continue, but the cause should be investigated
Ex. WL max deltas of 0.8 - 0.9. It's still within tolerance, but it's just suspicious. Probably setup error
95
Describe action level 2
Scheduled action
Results of QA procedure that are at or near tolerance
Should cause investigation or scheduled maintence
If a single result exceeds tolerance value, but not by much, you should investigate or schedule maintence
Action: schedule time to correct within next week, but treatment may continue since clinical impact in short amount of time shouldn't be major
96
Describe action level 3
Immediate action or stop treatment or correction action
Malfunctions or excessive errors that are too significant
You need to stop treatment until it gets fixed
Ex. nonfunctional safety interlocks
Ex. Excessive error in dosimetric quantity (like output)
97
What equation for flatness does Khan use? What is the associated tolerance?
F = M-m/M+m *100%
| 3% tolerance
98
What equation for symmetry does Khan use? What is the associated tolerance?
Maximum percent difference from two symmetrically flipped points
2% tolerance
99
In what region of the field are flatness and symmetry defined?
The central 80% dose region
100
Typical dose for Varian OBI (CBCT)
0.2 - 2.0 cGy
101
How often should you measure imaging dose for OBI and CT?
Annually for both
102
What image quality tests are required monthly for OBI?
```
Scaling
Uniformity
Noise
High contrast spatial resolution
Low contrast detectability
```
* CT number accuracy (but only if IGRT is used for dose calculation)
103
What are the recommended daily tests for CT based IGRT systems? And their respective tolerances (from TG-179. Not the TG-142 tolerances)
Safety (collision interlocks, warning lights)
Laser/image/treatment isocenter coincidence (+- 2mm)
Phantom localization and repositioning with couch shift (+- 2 mm)
104
How does EPID spatial resolution compare with the array devices we use (ArcCheck and MapCheck)
Better spatial resolution than both of them
105
How does EPID buildup compare with the array devices we use?
Insufficient buildup needed get dose due to lack of buildup material (the copper plate used for buildup on the portal imager is not sufficient to simulate buildup as would be seen for tissue)
106
What are typical gamma analysis tolerance values?
What do we use?
Either 3%, 3 mm, 5-10% threshold
or
2%, 2 mm, 5-10% threshold
or
somewhere in between (ex. we use 3%, 2 mm, 10% threshold for our arrays and 1 mm for film)
107
In what region (high or low gradient) is the dose difference test most sensitive? In what region is the DTA test most sensitive?
Dose difference most sensitive in low dose gradient region
DTA most sensitive in high dose gradient region
108
Before Gamma Analysis, what method was used for reference vs measurement analysis?
DTA/Dose Difference test
Only one of the two needed to pass, and you apply them separately depending on the dose gradient region. This is unlike GammaAnalysis where both DTA and Dose Diff are analyzed at the same time.
109
What is a passing gamma value?
Anywhere from 0 to 1
110
What is the difference between global dose normalization and local dose normalization? Which do we typically use?
Global dose normalization normalizes the dose difference to a single constant value (this is typically the global maximum). This puts much more emphasis on therapeutic relevance and eases the comparison in the out-of-target region.
Local dose normalization normalizes to a reference dose at the local point. In general this increases the stringency of the test in all regions, both high and low.
We use global dose normalization
111
If your IMRT QA plan fails, what order of troubleshooting is recommended according to TG-218?
1. check your setup
2. Measure again but with slightly lower tolerance
3. Make sure beam characteristics are consistent with baseline
4. Investigate any possible MLC errors
5. Investigate any possible TPS discrepancies
112
What are some sources of possible error in a TPS system that calls for the need of IMRT QA? (I have 9 written down. Try to get as many as possible)
1. MLC lead end modeling
2. MLC tongue-and-groove modeling
3. MLC leaf transmission modeling
4. Collimator transmission modeling
5. Field edge penumbra modeling
6. Small field output factors
7. Off-axis profile modeling
8. Choice of dose calc grid size
9. Mechanisms for accounting for hetereogeneities
113
What are some sources of LINAC performance errors that calls for the need of IMRT QA? (I have 5 written down.)
1. MLC leaf position errors
2. MLC leaf acceleration
3. Gantry rotation errors
4. Beam stability
5. Isocenter
114
What are some sources of measurement performance errors that can occur during IMRT QA? (I have 5 written down.)
1. Diode sensitivity degradation over time
2. Chamber leakage
3. Misalignment
4. Improper background corrections
5. Global vs local dose normalizations
115
What is the official TG-218 recommended gamma anlysis criteria for IMRT QA?
3% / 2 mm - 95% passing
| It's what we use
116
What are some tests that may be performed during IMRT commissioning? There's two types. Don't go too much into detail, just be somewhat familiar.
Measurement and gamma analysis of test plans in TPS vs film measurements in a homogenous phantom. The test plans are simplified versions of actual plans, like prostate, H&N, APPA, a C shaped target and surrounding avoid structure, etc.
A "chair" pattern field test that tests sliding window IMRT. It's recommended in the Van Esch paper. It has three profiles/regions, a zer dose region (that is only leaf transmission), a homogenous region, and a zero fluence (sliding leaves) region
