Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

QA > machine QA > Flashcards

machine QA Flashcards

1
Q

describe E2E test for stereo

A

Use hidden targets in a phantom
Localize with CT/MR and complete a treatment plan
Treat with beams and also use film to get exposure
Displacement of image of target from radiation exposure should be < 1 mm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How do you measure dose profile for gamma knife?

A

plug 200 of 201 collimators and use film dosimetry. Also plug all 201 collimators to get background.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

definition of nominal stereo

A

sphere within which gantry, couch, collimator intersect

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what tests should be performed for new ion chambers

A

-stem effect (worse for small fields)
-radiographs for mechanical soundness
-leakage current (10 ^ -14) A
-quantify stem effect
-microphonics- place cables etc under stress and test of current measured changes
-measure radiation equilibration time – at most 2 X 200 cGy readings
-test atmospheric communication- chamber should obey ideal gas law
-ensure polarity effect < 1 %
-measure collection efficiency; recombination should be < 1.02
-check orientation dependence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

pros and cons of diodes

A

-smaller volumes and higher sensitivity than ion chambers
-include silicion (high Z) which leads to energy dependence
-directional dependence
-lose sensitivity over time

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

pros and cons of diamond detectors

A

-almost soft-tssue equivalent, but higher density than water 93.5 g/cm3)
-very sensitive
-good mechanical stability
-sensitivy doesn’t change with radiation
-small directional dependence
-dose rate dependence

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

desriable properties of electrometers

A

accurate, linear, stable, sensitive, high impedance, low leakage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what are the options for 2D dosimetry

A

film, computed radiography, diode arrays, ion chamber arrays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

List TG-142 tests where constraints for stereo are different than for conventional

A

o Daily:
 Laser localization: 2, 1.5, 1 mm
 Collimator size indicator: 2, 2, 1 mm
o Monthly:
 Couch position indicators: 2 mm/1º, 2 mm/1º, 1 mm/0.5º
 Lasers: 2, 1, <1 mm
o Annual:
 Coincidence of mechanical and radiation isocenters: 2, 2, 1 mm from baseline
o Daily imaging:
 Positioning/repositioning for planar kV, EPID MV: 2, 2, 1 mm
 Imaging and Tx coordinate coincidence for all: 2, 2, 1 mm
o Monthly imaging:
 Imaging and Tx coordinate coincidence for planar kV, EPID MV: 2, 2, 1 mm
 Planar kV scaling accuracy: 2, 2, 1 mm
 CBCT geometric distortion: 2, 2, 1 MM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

how do you check that the ion chamber is on CAX?

A

take measurements by rotating collimator at different angles
-if not at CAX, readings will be different because x and y jaws are at different heights

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

consideration for FFF beam (additional correction)

A

Prp correction from TG51 addendum
/(average field intensity across chamber sensitive volume, normalized to 1 at centre of sensitive volume)  Prp will be >1 to correct for doses being generally lower away from CAX for FFF beams.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

how to use shielded diodes?

A

scan direction matters, especially with shielded diodes since the shielded is not uniform around the active material. Should scan right-left, then scan left-right, and then average the two scans (this is referred to as hysteresis)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

2 things you can get from starshot test

A

-size of radiation isocenter
-distance from radiation isocenter to mechanical isocenter (must put bb at intersection of crosshairs to indicate where mechanical isocentre is)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

2 competing effects for Pfluence in electron beams

A

-in-scatter effect which increases f;luence in the cavity because electrons are not scattered out by the gas in the cavity
-obliquity effect- decreases fluence in cavity because electrons go straight instead of being scattered

Pfl < 1 which means the in-scatter dominates, making the observed fluence too large. Note that the correction is
very large at low-energies or for large diameter chambers and in this case it is best to use plane-parallel chambers with large guard rings.

-dominance of in-scattering over out-scattering gives rise to increase of fluence towards back of cavity and hence an increase ovf the reading of an ion chamber where electrons can enter at different dephts (i.e. cylindrical ones)

-PP chambers reduce fluence effects

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

why do we monitor the pulse rate with the reference chamber?

A

so that we can account for any pulse drops in the flatness/symmetry scan

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

where do you get best measure of flatness/symmetry?

A

horn on beam profile (as opposed to 10 cm depth)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

where should reference chamber be placed?

A

in corner of treatment field but not too close to the scan chamber (as it cause cause scatter into the measurement area)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

how much does output change with FS at 10 cm depth?

A

87 % for 4x4, 110% at 20x20, and 119 % for 40x40 compared to 10x10

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

how is scatter from the linac arm compensatred for?

A

-older true beams and clinac have a correction factor for scatter from the linac arm; newer true beams have a lead coating to minimize the effects of this scatter

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

define hysteresis

A

the dependence of the state of a system on its history. For example, a magnet may have more than one possible magnetic moment in a given magnetic field, depending on how the field changed in the past

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

if you drift 10% on unservoed dose rate, how much would you drift on servoed dose rate

A

1%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

acceptable electrometer leakage

A

0.1 pA without beam on
dose rate is significant if electrometer is leaky- a slower dose rate can give a larger reading

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

how to tune machine if it is running hot?

A

increase gain- machine collects more charge- machine runs less hot

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

why does linac output almost always trend up?

A

ion chambers leak air over time
-chamber doesn’t collect as much charge with less air so the machine pushes out more

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
linac output is trending down- what could it be?
hole in target
26
what QA is required if you switch ion chamber on linac
annual QA
27
how does dose rate affect recombination?
-faster dose rate= short time interval of pulse vs ion collection time – more time for recombination to occur -Pion = 1.006 on 6FFF TB4 -Pion = 1.003 on 6x TB4 -Pion ~ 1.01 for electron beams -different because dose/pulse of low E beams is 0.03 cGy/pulse 0.06 cGy/pulse for FF beams 0.08 cGy/pulse for electron beams Dose per pulse in the unit of monitor units per pulse (MU/pulse) is dose rate (MU/min) divided by pulse rate (pulse/min). Since pulse rate of the linear accelerator for the same nominal energy does not change, Pion becomes a function of the dose rate of the photon beams.
28
2 types of reombination
initial and general recombination. The former process occurs most likely in densely ionized track such as α‐particles and is independent of dose rate. The latter process occurs when positive and negative ions from different tracks re‐combine on their way to the collecting electrode and is dose‐rate dependent.
29
dosimetric advantages of FFF
lower head scatter and lower out‐of‐field radiation -FFF has similar dmax to FF because less electron contamination pushes dmax in but softer beam pushes it more shallow- combined effects Also, variation in output factor is reduced when the filter is removed. Sc can change ~ 8 % when the field is changed from 3x3 to 40x40. This is reduced to 1-3% for FFF. Also, energy spectrum is essentially the same across the profile of FFF beams. Leaf transmission also reduced because of softer beam spectrum, which can improve calcs for some plans. -With IMRT, filter not required since MLCs deliberately modulate intensity of beam- can get higher dose rate by using FFF -may increase skin dose since beam isn’t being hardened
30
daily electron and x-ray output constancy
3 %, TG 142
31
daily laser localization
2 mm non IMRT 1.5 mm 1MRT 1 mm SRS/SBRT TG-142
32
Daily ODI treshold
2 mm non IMRT 2 mm IMRT 2 mm SRS/SBRT TG-142
33
daily colli size indicator
2 mm non IMRT 2 mm IMRT 1 mm SRS/SBRT TG142
34
daily safety checks
door interlock beam off LPO interlock key turns beam off LPO times out indicator lights audiovisual monitors
35
monthly electron and x-ray output treshold, backup monitor chamber constancy
2% TG142
36
monthly dose rate constancy
2% TG142
37
monthly photon and electron beam profile constancy
1% TG142
38
monthly energy constancy
1% TG142
39
Monthly light/rad coincidence
2 mm or 1 % on a side for symmetric 1 mm or 1 % on a side for asymmetric TG142
40
monthly distance check for lasers
1 mm for stereo and IMRT, 2 mm for 3D TG142
41
monthly gantry/colli indicators
1 degree TG142
42
Monthly jaw position indicators
2 mm symmetric 1 mm asymmetric TG142
43
Monthly cross-hair walkout
1 mm TG142
44
Monthly treatment couch position indicators
2 mm/1 degree 1 mm/0.5 degrees for stereo TG142
45
monthly respiratory gating tests
beam outpout constancy within 2 % -phase amplitude, beam control work respiratory monitoring works gating interlock works
46
annual x-ray and electron flatness and symmetry change from basline
1% TG142
47
Annual SRS arc rotation mode
monitor units set vs delivered, 1 MU or 2% (whichever is greater) gatry arc sec vs delivered 1 degree of 2 % (whichver is greater) TG142
48
annual output calibration
1% TG142
49
Spot check of field size dependent output factors for photons (annual)
2% for FS < 4X4 1 % for FS > 4X4 TG142
50
Ouput factors for electron applicators (1 FS/energy) annual
2 % from baseline TG142
51
annual x-ray beam quality
1 % from baseline PDD10 or TMR20/TMR10 TG142
52
annual electron beam quality
R50 within 1 mm TG142
53
annual physical wedge transmission accuracy
2% TG142
54
annual electron monitor unit linearity
2 % if > 5 MU TG142
55
annual x-ray monitor unit linearity
2 % if > 5 MU 5 % if 2-4 MU TG142
56
ANNUAL x-ray output constancy vs dose rate
2 % from baseline tg142
57
annual electron OR X-RAY output constancy vs gantry angle
1% from baseline TG142
58
annual electron and x-ray OAF constancy vs gantry angle
1% from baseline TG142
59
annual PDD or TMR and OAF constancy for TBI/TSET
1% (TBI) or 1 mm (TSET) shift from baseline TG142
60
annual TBI/TSET output calibration
2% from baseline TG142
61
ANNUAL TBI/TSET accesorries
2% from baseline TG142
62
Annual colli rotation isocenter
1 mm from baseline TG142
63
annual gantry rotation isocenter
1 mm from baseline TG142
64
annual couch rotation isocenter
1 mm from baseline TG142
65
Annual coincidence of mechanical and radiation isocenter
2 mm 1 mm for stereo TG142
66
Annual table top sag
2 mm TG142
67
Annual beam energy constancy for respiraoty gating
2%
68
annual temporal accuracy of phase/amplitude gate on annual calibration of surrogate for respiraroty phase/amplitude interlock testing for gating
100 ms of expected 100 ms of expected interlock functional TG142
69
MLC qualitative test (like picket fence)
weekly look for visible deviations
70
monthly MLC leaf tests TG142
setting vs radiation field for 2 patterns (within 2 mm) travel speed- loss of lead speed > 0.5 cm/s fails leaf position accuracy within 1 mm for four cardinal gantry angles
71
annual MLC transmission (average of leaf and interleaf transmission, all energies)
0.5 % from baseline TG142
72
Annual MLC leaf position repeatability
1 mm TG142
73
Annual MLC spoke shot
1 mm radius TG142
74
annual MLC Coincidence of light field and x-ray field (all energies)
2 mm TG-142
75
segmental IMRT step and shoot test, annual for MLC
< 0.35 cm max , error RMS, 95% of error counts < 0.35 cm TG142
76
MLC annual test moving window IMRT (4 cardinal gantry angles)
< 0.35 cm max, error RMS, 95% of error counts < 0.35 CM TG142
77
daily kV/MV imaging QA
collision interlocks positioning/repositoning < 2mm, <1 mm for stereo imaging and treatment coordinate coincidence, < 2 mm, <1 mm stereo TG142
78
Daily CBCT imaging QA
collision interlocks positioning/repositoning < 2mm, <1 mm for stereo imaging and treatment coordinate coincidence, < 2 mm, <1 mm stereo TG142
79
Monthly planar MV QA
imaging and treatment coordinate coincidence, <2 mm, < 1 mm stereo scaling < 2mm spatial res., contrast, uniformity and noise are baseline TG142
80
monthly planar kV imaging QA
imaging and treatment coordinate coincidence, <2 mm, < 1 mm stereo scaling < 2mm, < 1 mm if stereo spatial res., contrast, uniformity and noise are baseline TG142
81
CBCT monthly imaging QA
geometric distortion < 2mm, < 1 mm if stereo spatial res., contrast, HU constancy, uniformity and noise all baseline TG142
82
annual planar MV imaging QA
full travel SSD within 5 mm imaging dose is baseline TG142
83
annual planar kV imaging QA
beam quality/energy and imaging dose are baseline TG142
84
annual CBCT QA
imaging dose is baseline TG142
85
CPQR daily lasers/crosshairs
1 mm tolerance, 2 mm action
86
CPQR daily optical distance indicator
1 mm tolerance, 2 mm action
87
optical back pointer CPQR daily
2 mm tolerance, 3 mm action
88
CPQR daily field definition jaws/MLC leaves
1 mm tolerance, 2 mm action
89
CPQR daily output constancy photons and electrons
2% tolerance, 3 % fail
90
CPQR daily wedge factors
2% tolerance, 3 % action
91
CPQR mothly gantry and colli angle readout
0.5 degree tolerance, 1 degree action
92
CPQR monthly cross-hair centering/ colli rotation isocenter
1 mm tolerance, 2 mm fail this is diameter (fail matches TG142 condition of radius of 1 mm)
93
CPQR couch position readout monthly
1 mm tolerance, 2 mm fail
94
CPQR couch rotation isocenter monthly
1 mm tolerance, 2 mm fail
95
CPQR couch isocentric angle monthly
0.5 degrees tolerance, 1 degree action
96
CPQR optical distance indicator monthly
1 mm tolerance, 2 mm action
97
CPQR monthly relative dosimetry
2% tolerance, 3 % fail
98
CPQR monthly central axis depth dose reproducibility
1%/2 mm tolerance 2%/3mm action
99
CPQR monthly beam profile constancy
2% tolerance, 3 % action constancy can be calculated as an average value of chosen off axis points in the beam profile
100
CPQR monthly light to rad coincidence
1 mm tolerance, 2 mm action
101
CPQR monthly jaw position accuracy
1 mm tolerance, 2 mm action
102
CPQR monthly MLC leaf position accuracy
1 mm tolerance, 2 mm action
103
CPQR dynamic leaf position accuracy monthly (picket fence)
0.5 mm tolerance, 1 mm action
104
CPQR dynamic MLC fluence delivery (i.e. verification) monthly
95 % <3%/3 mm tolerance 95 % <5%/3 mm action
105
CPQR annual profile reproducibility
2% tolerance, 3 % action
106
CPQR annual depth dose reproducibility
1% tolerance, 2 % action
107
CPQR reference dosimetry annual
1% tolerance, 2 % action
108
CPQR annual relative output factor reproducibility
1 % tolerance, 2 % action
109
CPQR annual wedge and accessory transmission factor reproducibility
1 % tolerance, 2 % action
110
CPQR annual wedge profile reproducibility
1 % tolerance, 2 % action
111
CPQR profile and output reprducibility vs gantry angle
1% tolerance, 2 % action
112
CPQR annual monitor chamber linearity
1%/1MU tolerance 2%/2MU action
113
CPQR annual end monitor effect
0.5 MU tolerance 1 MU action
114
CPQR annual collimator radiation isocenter
1 mm tolerance 2 mm action
115
CPQR annual gantry rotation isocenter (mechanical and radiation)
1 mm tolerance 2 mm action
116
CPQR annual couch rotation isocenter (radiation)
1 mm tolerance 2 mm action
117
CPQR annual coincidence of mechanical and radiation isocenters
1 mm tolerance 2 mm action
118
CPQR annual coincidence of axes of rotation
1 mm tolernce 2 mm action
119
CPQR annual couch delfection
3 mm tolerance 5 mm action
120
CPQR annual leaf transmission (all energies)
1% tolerance 2 % action
121
CPQR annual leakeage between leaves (all energies)
2% tolerance 3% action
122
CPQR annual transmission through abutting leaves
2% tolerance 3% action
123
CPQR annual leaf alignment with jaws
0.5 degree tolerance 1 degree action
124
CPQR annual dosimetric leaf gap
0.2 mm tolerance 0.3 mm action
125
what is dosimetric leaf gap
plot MLC leaf transmission as function of gap width extrapolate width for which transmission = 0
126
why do we QA couch sag?
a shift of the entire couch is not a big deal because we have imaging. However, if the couch sags un-evenly, the beam could land obliquely on the patient- could have dosimetric consequences
127
can you still treat if a laser stops working?
theoretically can’t treat according to TG142, but in reality we have imaging such that we could treat safely
128
describe a clinical scenario where light to rad test is relevant
- Back in the days before imaging, might set up a patient using the light field. In this case, if we have 2 mm uncertainty on each side (per light to rad requirement), could potentially be 4 mm off at the junction of the 2 fields (cranial spinal)
129
why would field sizes fail QA or L2R test?
-mirror that bends the light (light cannot go through beam!) could be badly placed; light source could be badly placed

QA (8 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions