Numbers to memorize Flashcards
1
Q
What is the probability of dying from cancer given some exposure? Which report gives these values?
A
4% / Sv for chronic exposure
8% / Sv for acute exposure
BEIR V
2
Q
Above what whole body dose is there a nearly 100% lethality?
A
6 Gy
3
Q
What voltages is the GM region in?
A
1000 - 1400 V
4
Q
List the following imaging techniques from highest to lowest spatial resolution
Nuc med scans
Digital subtraction angiograms
CT and MRI scans
Computed radiography
A
Computed radiography (2048 x 2048)
Digital subtraction angiograms (1024 x 1024)
CT and MRI scans (512 x 512)
Nuc med scans (128 x 128)
5
Q
What is the typical axial resolution of an ultrasound?
A
0.5 mm
6
Q
Per TG-128, what is the tolerance for depth of penetration test?
A
1 cm
7
Q
What is the NCRP 147 exposure in any one hour limit?
A
0.02 mSv in any one hour
8
Q
What is a typical DLP for helical CT?
A
Hundreds of mGy*cm
9
Q
What is a typicaly CTDI for helical CT?
A
20 - 80 mGy
10
Q
Which TG report outlines QA for gamma knife?
A
TG 148
11
Q
Per TG-66, for laser tests, what is spatial tolerance
For all other distances, what is spatial tolerance?
A
Laser tests - 2 mm
Other distances - 1 mm
12
Q
Per NCRP 147, what is the shielding design limit for controlled and uncontrolled areas?
A
Controlled: 0.1 mSv/wk
Uncontrolled: 0.02 mSv/wk
13
Q
Which TG report gives guidance on PET/CT shielding?
A
TG 108
14
Q
What is the half-life of F-18?
A
110 mins
15
Q
How far do emitted positrons of F-18 travel before annihilation on average?
A
1 - 2 mm
16
Q
What is the resolution in a typical PET scanner?
A
6 - 10 mm
17
Q
Typical dose to patients from a PET/CT
A
25 mSv per scan
18
Q
What is the typical shielding in inches of lead of a CT sim?
A
1/16” lead
19
Q
What is the typical shielding of a PET/CT suite?
A
1-2 cm of lead
20
Q
What is the typical shielding of an HDR suite?
A
50 cm of concrete
21
Q
What is the typical shielding of Co-60 suite?
A
70 cm of concrete
22
Q
Which TG report focuses on QA of TPS and when did it come out?
A
TG-53
1998
23
Q
What is the half-life of I-131?
A
8 days
24
Q
What is the dose range of EBT 3 Film?
A
0.2 Gy to 10 Gy
25
What is the shielding for a Linac vault?
Primary barrier: 2 - 3 m of concrete
Secondary barrier: 1.5ish m of concrete
26
What is typical shielding for a Cyberknife vault?
170 cm of concrete
27
What is a typical Pion value for farmer chambers for...
Flat photon beams
FFF photon beams
Electron beams
Flat photon beams: around 0.2 or 0.3% and increase with energy
FFF photon beams: around 1-2% and increase with energy
Electron beams: around 1.5% for all energies
28
What is the acceptable dose to radiation workers and general public and why are these numbers different?
Worker: 50 mSv/yr whole body
Member of public: 1 mSv/yr whole body
1) Radiation workers are informed about the risks of working with radiation and methods to reduce radiation, thus they can make informed consent decisions
2) Extra exposure may be necessary in the performance of their job
29
How thick is the lead foil used in TG-51, and how far from water surface do we keep the foil?
1 mm thick lead foil
30 cm from water surface used due to clearance issues (50 cm not achievable)
30
What are some typical collection volumes for...
Farmer chambers
Scanning ion chambers
Microchambers
Farmer chambers: ~0.6 cc
Scanning ion chambers: ~0.1 cc
Microchambers: ~0.01 cc
31
What is approximate bremsstrahlung contamination relative to Dmax for 4 MeV to 20 MeV beams?
~1% for 4 MeV
~4% for 20 MeV
32
How many prostate seeds are placed in a patient?
Around 50 - 120 seeds
33
How wide is a typical prestine bragg peak for proton beams and what influences the width?
2 - 6 mm
* As energy increases, depth of penetration increases, thus more range straggling which widens the peak
* Material heterogeneity intersecting only part of a beam will also increase range straggling, causing a larger peak width
34
What is typical prescription in H&N?
High risk: 70 Gy in 35 Fx
Intermediate risk: 63 Gy in 35 Fx
Low risk: 56 Gy in 35 Fx
I've also seen
70 Gy in 35 Fx (with final 10 being a CD boost)
50 Gy in 25 Fx
35
For H&N treatments, what is the go to dose constraint resource typically. And what are the constraints for...
Cord
Brainstem
Parotid
Mandible
Esophagus
Cord: Dmax < 50 Gy
Brainstem: Dmax < 54 Gy
Parotid: Dmean < 20 Gy (single), Dmean < 25 Gy (both)
Mandible: Dmax < 70 Gy
Esophagus: Dmax < 74 Gy + other volumetric doses
36
What are the standard occupational dose limits for adults as outlined by 10 CFR 20?
Total effective dose equivalent (whole body) < 50 mSv/yr
Sum of deep and committed dose equivalent < 500 mSv/yr
Lens < 150 mSv/yr
Shallow, skin, extremities < 500 mSv/yr
37
What is the efficiency range of MV photon beam bremmstrahlung production of Linac targets per Khan?
30 - 95%
38
What are typical transmisison factors through...
Primary collimator
jaws
MLCs?
Primary collimators: 0.1%
Jaws: <2%, in practice around 0.5%
MLCs: <5%, in practice around 1-2%
39
What is the rule of thumb for out of field dose at 10 cm and 30 cm from photon field edge?
10 cm: 1% of CAX
30 cm: 0.2% of CAX
40
Per TG 36, at what dose level does risk to fetus become "significant?"
0.1 - 0.5 Gy during the first trimester
41
Which NCRP report contains a table of tissue weighting factors for effective dose equivalent? What tissue has the highest factor?
NCRP 116 contains the table
Gonads has the highest factor at 0.2
42
At what threshold dose does GI acute syndrome occur?
6 Gy total body dose
43
Per NRC regulatory guide 8.29, what is the estimated loss of life expectancy for a radiation worker? What is responsible for this loss?
On average, a loss of 20 days is expected
This is caused by delayed effects caused by chronic exposure to low doses of radiation, primarily cancer induction
Single radiation accidents actually contribute very minimally to overall life expectancy loss across the entire population, as they do not occur that often
44
What is the approximate fade of TLDs over the course of a month?
Approx 1%/month fade
45
Per TG-51 addendum, what are the criteria for a ion chamber to be classified as a reference class ion chamber?
Calibration not varying by more than 0.3% over two years
Pleak < 0.1%
Ppol < 0.4%
Pion < 1.05
Pion Cinit component < 0.2%
Pion Cgen component scaling linearly with dose per pulse
Pion between opposite polarities shoukd agree within 0.1%
Chamber settling spread < 0.5%
46
What TG report gives recommendations on the QM of EBRT data transfer?
TG 201
47
What are the Dmax constraints for spinal cord for 1, 3 and 5 Fx SBRT per TG 101?
1 Fx: Dmax < 14 Gy
3 Fx: Dmax < 21.9 Gy
5 Fx: Dmax < 30 Gy
48
What is the energy of F-18 emitted positron and approximately how far will it travel before annihilation?
On average 0.63 MeV
Will travel mean distance of 2.4 mm before annihilation
49
Approximately what output factor do you expect to measure for a 2x2 cm2 field relative to 10x10 cm2? What about for a 0.5 x 0.5 cm2 field?
2x2 cm2 field: approx 0.8
0.5 x 0.5 cm2 field: approx 0.4
50
What are typical dose rate constants for common HDR sources? How do you determine it?
Constants are published by TG-43U1 and TG-43
Typical values are around 1 - 1.1 cGy / hr U
51
When was NJ set as an agreement state?
2009
52
What is the limit of AAPM gift from vendor? Can this be exceeded? What if a vendor takes you to dinner?
$100 per the AAPM code of ethics and professionalism
Exception being for education
Dinners can be appropriate, as long as they are not extravagent, per AAPM
53
What three survey meters do we have in our department?
Victoreen 450A and 450B
Ludlum 3
54
Which article containts most NJ state regs?
NJAC Title 7 Ch 28
55
According to our RAM license, what is the maximum activity of Co-60 and Ir-192 we are allowed to have in the facility at any given time?
Co-60:
6600 Ci total, cannot exceed 36 Ci for any one source and mean must be < 34 Ci
Ir-192
21 Ci total, cannot exceed 12 Ci for any one source
56
How does the depth of dref compare with dmax?
dref is generally at about dmax for lower energy fields, and is deeper than dmax for higher energy fields
For 12 MeV or less, dref is approximately at the 100% isodose line
For 20 MeV, dref is approximately at the 95.5% isodose line
57
What is the approximate error in PDD(dref) if you forget to convert from I50 to R50?
Approximately 3 - 5% error
58
Per TG 40, what is HDR source timer accuracy requirement?
1%
So if 100 seconds is used, tolerance is 1 second
59
What is the relative accuracy of a geiger counter? What is the device typically used for?
Accuracy of +- 20%
Used mainly for detecting presence of low levels of radiation. Ideally suited for leak testing, contamination testing, and some radiation survey applications
60
Which TG report is used that gives recommendations on how many and what tolerance LDR sources should be assayed to? What are the tolerances and # of seeds to assay?
TG 56
* 10% of seeds should be assayed
* Mean batch strength should be within 3% of manufacturer strength
* Each seed should also be within 5% of manufacturer stated strength
61
What diseases are typically treated using TBI, and what are the prescriptions?
Bone marrow transplant (immune system suppression prior in conjunction with the transplant to reduce likelihood of transplant rejection disease)
* 150 cGy x 8 fractions or 200 cGy x 6 fractions (dose rate kept around 10 - 20 cGy/min)
* Typically delivered BID
* Prescription point is umbilicus
Eradication of malignant hematopoietic cells (leukemias or lumphomas) or those effected by genetic disorders
* 2 Gy in a single fraction (dose rate kept around 10 - 20 cGy/min)
* Prescription point is umbilicus
62
What is typical volume, length and radius of a farmer chamber? What is the wall typically made of? What baout central electrode?
Volume: 0.6 cc
Length: 2.3 cm
Radius: 3 mm
Wall is typically graphite and plastic
Central electrode is typically aluminum
63
Where is EPOM for your farmer chamber for photons and electrons?
0.18cm upstream for photons
0.15cm upstream for electrons
64
What is typically being treated in CSI and what is a typical prescription? How effective is it?
CSI is a curative technique for **medulloblastoma (most common)** and also (leukemia/lymphoma, intercranial germ cell tumor, pinealoblastoma, ependymoblastoma) by treating everywhere the cerebrospinal fluid flows
30 - 36 Gy in 18 - 21 Fx (1.5 - 1.8 Gy/fx)
followed by 18 - 20 Gy in 10 - 11 fx for posterior fossa or tumor bed
Alternatively, 23.4 Gy in 18 Fx followed by 30.6 Gy boost to posterior fossa
Curative treatment in about 70 - 85% of average risk patients
65
How far laterally do the spine fields in CSI extend, and where do they match one another? At what level does the top spinal field match the craniel fields?
Match at approximately L2/L3 vertebrae
Extend laterally 1 cm beyond vertebrae (5 - 7 cm field size lateral)
Match with cranial fields around C3/C4 (2 cm flash beyond skull)
66
What is the energy of BPE neutron capture gammas?
0.48 MeV from boron component (most common)
2.2 MeV from hydrogen
67
What is the the neutron TVL for BPE?
4.5 cm
68
What are typical concrete thicknesses for primary and secondary barriers in a high energy LINAC vault? What about door thickness with and without maze?
Primary: 1.5 - 3 m concrete
Secondary: 1 - 1.5 m concrete
Door with maze: 0.5 - 2cm inner lead, 2-4 cm BPE, 1 cm outer lead
Door no maze: 5-9cm inner lead, 15-25 cm BPE, 1 cm outer lead
69
Per NCRP 151, what occupancy factor is used for corridors? What about vault door? What about stairways?
Corridors: 1/5
Vault door: 1/8
Stairways: 1/40
70
What is the use factor of barriers 2 and 3?
Approximately 21.3
Per NCRP 151, AP/PA treatments increase the use factor for 0 and 180, hence they are > 25%. So 90 and 270 deg are less than 25%
AP (0 deg, down) has the highest use factor at 31%, PA (180 deg, up) has a use factor of 26.3
71
How much of a dose shadow do you expect to see for diodes? What is, reduction of skin dose?
Up to 10% for photons
Up to 20% for low energy electrons
But keep in mind, diodes are not placed every fraction, and if they are, they can be placed in different locations. Meaning the overall shadow across all treatments is minimal
72
What is tenth-value distance in linac vault shielding? How long is a typical TVD? What factors impact it?
TVD is the maze distance required to reduce photon and thermal neutron fluence by a factor of 10
Typical TVD is 4 - 5 meters (a typical maze is usually around 8 meters long)
Height and width of the maze impact TVD. That is...
TVD approximately equals 3 * sqrt (H x W)
73
By about what factor do proton plans reduce integral dose relative to IMRT/VMAT and 3D plans?
2-3x less integral dose than IMRT/VMAT
2-7x less integral dose than 3D plans
74
What is Bremsstrahlung energy efficiency for...
Superficial therapy units
Orthovoltage therapy
MV therapy
Superficial: 0.5%
Orthovotlage: 2%
MV: 30% and higher
75
What are the common kV therapy energy ranges? What are some applications?
**Grenz Rays:** 10 - 20 kV, no longer in clinical use due to air attenuation
**Contact therapy:** 20 - 50 kV. Such a short range, they're really only useful when placed in close contact with tissue. Ex. include electronic brachytherapy and IORT
**Superficial:** 50 - 150 kV. Most common range. used for superficial skin lesions up to 5 mm @ 90% isodose
**Orthovoltage:** 150 - 500 kV. Up to 2 cm @ 90% isodose
**Supervoltage:** 500 - 1,000 kV. No longer clinically used
76
Generally, what are approximate doses of the following imaging procedures...
kV planar
kV CBCT
MV EPID
MV CT Imaging
MC CBCT
Where are these values from?
Per TG 180
kV planar - 0.1 - 1 cGy
kV CBCT - 0.1 - 3 cGy (or 0.3 - 6 cGy for bone)
MV EPID - 1 - 4 cGy (1-2 cGy for 2.5MV)
MV CT Imaging - 1-3 cGy
MV CBCT - 2 - 12 cGy
77
Which TG report gives recommendations on QA of CT based IGRT systems?
TG 179
78
What are some typical annual dose equivalent readings for the following staff members...
Radiation Therapists
Physicist involved in brachytherapy
Nuc med techs
Special procedure radiologists
Cardiologists
Radiation Therapists: < 0.1 mSv
Physicist involved in brachytherapy: < 1 mSv
Nuc med techs: 2-5 mSv
Special procedure radiologists: ~10 mSv
Cardiologists: 20 - 30 mSv
79
What is the cited accuracy of the Luxel+ OSLD badge you have?
+- 15%
80
What is the approximate reduction in barometric pressure vs altitude? What altitude do local airports provide barometric pressure at?
1 in Hg per 1000 Ft of altitude
Local airports typically provide pressure relative to sea level
81
As shown in TG-51, what is the spread in Kq values for given Q among different ion chambers?
1.5ish% spread
That is, all ion chambers have a kQ value for a given Q within 1.5% of one another
82
For Varian Linacs, how does photoneutron production increase as you go from 15 MV to 18 MV beams?
Increases by approx 60%
83
What is approximate primary beam thickness in concrete for two adjacent 18 MV vaults?
Approximately 2 m
84
Per 10 CFR 20, what is the total effective dose limit to members of the public?
1 mSv/yr
0.02 mSv in any one hour in an uncontrolled area
5 mSv/yr for visitors
85
For an unshielded patient, what is the out of field dose, 10 cm and 30 cm from field edge? What about if a bridge shield is used?
10 cm from edge = 1%
30 cm from edge = 0.2%
Bridge shield used: reduced by 50% (average dose of about 0.1% of CAX dose)
86
Per TG-36, at what dose level does risk to fetus become significant?
10 - 50 cGy
At around 100 cGy there is a 50% risk of malformation
87
What is approximate surface dose for...
Co-60
6MV
10MV
18MV
Co-60: 50%
6MV: 25%
10MV: 23%
18MV: 20%
88
What is the Roentgen to rad conversion factor (MV beam) for air? What about tissue?
Air: 0.876 cGy/R
Tissue: 0.97 cGy/R
89
What are our clinical TMR for a 10x10 cm2 field for...
6MV
6FFF
10MV
10FFF
15MV
6MV - 77.4%
6FFF - 73.9%
10MV - 84.3%
10FFF - 81.3%
15MV - 87.1%
90
What are our Edge commissioned R50 for a 10x10cm2 cone for...
6E
9E
12E
16E
20E
6E - 2.36 cm
9E - 3.58 cm
12E - 5.00 cm
16E - 6.64 cm
20E - 8.27 cm
91
What is the approximate pdd(10) for a 6MV beam? What is it in our clinic?
65-67%
In our clinic it's 66.9%
92
What is the approximate pdd(10) for a 6FFF beam?
63-64%
In our clinic it's 63.7%
93
What is the approximate pdd(10) for a 10MV beam?
73-75%
In our clinic it's 74.1%
94
What is the approximate pdd(10) for a 10FFF beam?
70-72%
In our clinic it's 71.1%
95
What is the approximate pdd(10) for a 15MV beam?
76-77%
In our clinic it's 77%
96
What is the approximate pdd(10) for a 18MV beam?
80%
97
What is the approximate dmax for a 6FFF beam?
1.4 - 1.5 cm
98
What is the approximate dmax for a 6MV beam?
1.4 - 1.5 cm
99
What is the approximate dmax for a 10FFF beam?
2.2 - 2.4 cm
100
What is the approximate dmax for a 10MV beam?
2.2 - 2.4 cm
101
What is the approximate dmax for a 15MV beam?
2.7 - 2.9 cm
102
What is the approximate dmax for a 18MV beam?
3.3 cm
103
What is the approximate pdd(10) for a Co-60 beam?
55%
104
If given E0, what is the approximate R80 in water? What about R90?
R80(cm) = E0/2.8
R90(cm) = E0/3.2
105
What is approximate dmax of a 6E beam?
1.2 - 1.3 cm
106
What is approximate dmax of a 9E beam?
1.9 - 2.1 cm
107
What is approximate dmax of a 12E beam?
2.8 - 2.9 cm
108
What is approximate dmax of a 16E beam?
3.0 - 3.1 cm
109
What is approximate dmax of a 20E beam?
2.5 cm
110
What is the approximate surface dose for electrons with energies between 6E and 20E, and how does it change with increasing energy?
78 - 95%
Increases with increasing energy
111
What is the approximate HU of fat?
-80
112
What is the approximate HU of CSF?
15
113
What is the approximate HU of blood and muscle?
40
114
What is the approximate Z of tissue?
7.4
115
What is the approximate Z of bone?
14
116
What is the approximate density of lead?
11.34 g/cc
117
What is the approximate density of tungsten?
19.25 g/cc
118
What typically classifies a teletherapy medical event in a state?
* Wrong patient or site
* Total dose differs by 20% (for treatments >3fx)
* Total dose differs by 10% (for treatments <= 3fx)
119
What is the quoted proton radiation weighting factor per 10 CFR 20?
10
120
What is the half-life of Co-60?
5.3 years
121
What is the half-life of Ir-192?
73.83 days
122
What is the half-life of I-125?
59.6 days
123
What is the half-life of Lu-177?
6.7 days
124
What is typical Z of a prostheses?
20 - 25
125
What is approxiate TVL for 6X and 18X in concrete?
6X - 37 cm
18X - 45 cm
126
At what skin acute exposure levels do you get...
Erythema
Wet Desquamation
radionecrosis
Erythema - 6 Sv
Wet Desquamation - 25 Sv
radionecrosis - 50 Sv
127
What is the risk for developing cancer over lifespan due to 100 mSv, compared to that of all other causes?
1% for radiation 100 mSv
42% for all other causes
128
What tissue has the highest tissue weighting factor? What about the lowest?
Gonads = 0.2 (highest)
Skin and bone surface = 0.01 (lowest)
Some others...
Colon, bone marrow, lung or stomach = 0.12
Esophagus, liver, bladder, chest or thyroid = 0.05
Rest of body = 0.05
129
Approximately how much of the electron kinetic energy is converted to microwave energy in a magnetron?
60%
130
What is typical radiation offset for MLCs?
0.4 - 1.1 mm
131
What is relative electron density of bone? What about dense bone?
Bone: 1.2ish
Dense bone: 1.8ish
132
Below what dose value is there no clear scientific evidence of any adverse health effects at chronic radiation doses?
Below 100 mSv
133
What dose rates characterize HDR? Where is the dose rate specified?
12 Gy/hr at prescription point
or 0.2 Gy/min
134
What dose rates characterize LDR? Where is the dose rate specified?
0.4 - 2 Gy/hr at prescription point
135
What is the average photon energy of Cs-137?
662 keV
136
What is the average photon energy of I-125?
28 keV
137
For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for...
Rectum
Bowel
Sigmoid
Bladder
Rectum: D2cc < 75 Gy
Bowel: D2cc < 75 Gy
Sigmoid: D2cc < 75 Gy
Bladder: D2cc < 90 Gy
138
Per TG-59, what is the rule of thumb for dose received for 10 minute exposure at 10 cm from a 10 Ci HDR source?
0.75 Gy
139
Up to what distance away from a Ir-192 source does inverse square effects dominate?
4 cm
140
What is the NRC limit on leakage levels for HDR afterloader units?
1 mR/hr at 10 cm from any surface of the afterloader
141
What are the requirements for White I, Yellow II and Yellow III labels?
White I: Surface <= 0.5 mrem/hr and not detectable at 1 meter
Yellow II: Surface <= 50 mrem/hr AND <= 1 mrem/hr at 1 meter
Yellow III: Surface > 50 mrem/hr OR > 1 mrem/hr at 1 meter
142
Per NRC 10CFR35, what is the maximum half-life a source may have to be allowed to be held for decay-in-storage and disposed of as regular trash?
120 days
(remember it as 2x half like of I-125)
143
What is the typical density of concrete?
2.35 g/cc
144
Per 10 CFR 20, what defines a radiation area?
An area in which expected exposure exceeds 0.05 mSv in 1 hr at 30 cm away from source or any surface that radiation penetrates
145
Per 10 CFR 20, what defines a high radiation area?
An area in which expected exposure exceeds 1 mSv in 1 hr at 30 cm away from source or any surface that radiation penetrates
146
Per 10 CFR 20, what defines a very high radiation area?
An area in which expected exposure exceeds 5 Sv in 1 hr at 1 m away from source or any surface that radiation penetrates
147
Per NRC, what is the approximate risk of fatal cancer from radiation exposure per rem?
1 / 2500 chance of fatal exposure per rem (10 mSv) of TEDE received
NRC Regulatory Guide 8.29
148
Assuming you get 10 mSv of exposure per year, what is the expected lost life expectancy and how does this compare to other industries?
51 days lost life expenctancy
The average across all industries is 60 days lost life expenctancy, so we're below average
149
What is the lot to lot variation of radiochromic film calibration?
+- 5% variation
150
What is the approximate nA/Ci for an HDR Ir-192 source that you should be reading with your well chamber?
What about for LDR sources?
8.7 nA/Ci
So for a 10 Ci source, you should expect approximately 87 nA
For LDR sources it's of course much lower, less than 1 pA
151
For APBI using balloon applicatory, what is the minimum distance of balloon surface to skin surface, and what is the maximum allowed skin dose?
Min distance is 7mm
Max allowed skin dose is 145% of prescription dose
152
What is the duty cycle of a Linac?
0.1%
Radiation is only on for a total of 1 ms for each second of "beam on" time
Pulse length is 4 us
Time between pulse intervals is 4 ms
**Time between electron bunches is 0.3 ns**
153
Approximate how much larger is photon mode current than electron mode current in a Linac?
100x
Photon mode is approximately 100 mA/pulse
Electron mode is approximately 1 mA/pulse
154
What is typical prescription for CSI?
1.8 Gy x 13 Fx = 23.4 Gy with CSI
1.8 Gy x 17 Fx = 30.6 Gy boosted to the posterior fossa
155
How often does a Varian MLC log file record MLC leaf positions?
Every 50 ms
156
What is te approximate coincidence time window used in PET imaging?
10 - 20 ns
157
How does neutron dose rate increase when you fully shut jaws (relative to open field)
Increases by about 75%
158
As a general rule of thumb, how much neutron dose at maze entrance do you get for a 20 MV photon beam per Gy at isocenter?
1 Gy photons at isocenter is approximately 1 uSv neutron dose equivalent at outer maze entrance
159
What is the typical dosimetric penumbra from MLCs?
4 - 7 mm
160
What is typical shielding for HDR in concrete and lead?
50 cm of concrete
5 cm of lead
161
By about how much can diode perturbation affect dose at 5 cm depth?
< 5% for correctly used diode energy
up to 10% for high energy diode used in low energy beam
162
What is the half-life of Pd-103?
17 days
163
What is the half-life of Cs-131?
9.7 days
164
What is the diameter of cyclotrons used in proton therapy?
3.5 - 5 meters
165
What is the diameter of synchrotrons used in proton therapy?
8 - 10 meters
166
What is the approximate range of correction factor for solid water to liquid water? That is...
CF = reading in water / reading in solid water
+- 1%
Usually CF > 1.000 for electrons and < 1.000 for photons
167
What is LDR prostate dose for Pd-103 and I-125, monotherapy?
Pd-103: 125 Gy
I-125: 145 Gy
168
What is the average size of a prostate? What is the average size of a prostate in patients with prostate cancer?
Average size of healthy prostate = 25 cc
Average size of prostate cancer prostate = 50 cc
169
For Pd 103 and I-125, what is the model calculated best time to perform prostate seed post plan?
Pd-103: 16 days
I-125: 42 days
Most of the time, Pd-103 is 2-3 weeks after and I-125 is one month after
There is a balance between not scanning too early (underestimating delivered dose), but also not scanning too late (overestimating delivered dose, since most of the dose was delivered when prostate is still with edema). The fraction of dose delivered with edema depends on the half-life of the isotope, and so shorter half-life isotopes, such as Pd-103, would deliver more dose with edema present than longer half lives, so you want to do the post plan sooner
170
Per TG 114, what is the recommended criteria for MU agreement between TPS calculation and MU verificcation program for simple field geometries and low density heterogeneities or small fields?
Simple geomtries: 2%
Small fields or low density heterogeneities: 5%
171
What tolerance do we use for flatness and symmetry annually? What is baseline?
+- 1% from baseline
For symmetry, baseline is 0
For flatness, baseline is whatever TPS gives
172
What is the air kerma rate constant for Ir-192? What about for I-125 and Pd-103?
Approximately 4 cGy cm2 / mCi hr
(depends on the exact model of the source)
For I-125 and Pd-103 it's about 1.3ish cGy cm2 / mCi hr
173
Do modern TPS algorithms have more or less trouble calculating FFF beams compared to flattened beams?
Less trouble
* Flattening filters are a significant source of head scatter and machine leakage
* Output factors vary more in flattened beams than FFF beams
* FFF beams yield less electron contamination
* FFF beams have a relatively constant energy spectrum across profile
* FFF beam profiles are less changing over depth
* FFF beams yield less leaf transmission due to the softer beam
All of these are things that modern TPS systems have difficulty modeling, and as such reducing these factors means FFF beams are easier to calculate more accurately
174
For FFF vs flattened beams, which will result in better portal dosimetry imaging (assuming correction for dose profile done in service mode)
FFF beams will have better portal imaging
* FFF beams are softer, meaning slightly better contrast
* FFF beams are softer, which also means increased sensitivity in the phosphor screen in the EPID
175
Besides gamma analysis, what are some other methods that can be used to compare two different dose distributions?
1. Dose difference
2. Distance to agreement
3. Dose distribtuion overlays
4. Combined Dose difference / DTA (composite analysis), only one needs to pass (either DTA or dose diff)
Interesting fact: Composite analysis is usually more sensitive than gamma analysis
176
What is the most commonly used gamma criteria? Which TG report suggested it?
3% / 3 mm, 95% pass rate, global normalization, TG-119
Note: TG-119 is actually the IMRT commissioning report
177
When performing IMRT QA using ion chamber, what dose difference relative to mean dose does TG-218 recommend for the maximum and minimum calculated doses in the ion chamber volume in order to reduce volume averaging effects?
5% within mean dose to volume
So both max and mean dose should be within +-5% of mean dose
178
Which TG report gives recommendations on patient specific IMRT QA? What is the recommended gamma criteria from this report?
TG 218
3% / 2mm, 10% dose threshold, 95% pass rate for tolerance limit, 90% pass rate for universal action limits
This is the exact same we used in CTCA ^
179
What are layers and thicknesses of layers for a direct shielded door used for a high energy linac vault?
0.25" steel casing
3" lead
11" of 5% BPE
3" lead
0.25" steel casing
180
For a 18 MV beam, approximately what percentage of the dose at the door is neutrons? What about leakage photons? What about neutron capture gamma rays?
Neutrons: 62%
Leakage: 30%
Neutron capture gamma rays: 8%
181
What 'a' values are used in gEUD calculations for...
Target, Parallel organs and serial organs?
Target: a = -10
Parallel organs: a = 1
Serial organs: a = 10 - 20
182
For conventional fractionation, what is the most common total lung constraint?
V20Gy <= 30% of total lung
183
What are some common lung fractionations?
60 Gy in 30 Fx
45 - 50 Gy in 20 - 25 Fx
48 - 60 Gy in 3-5 Fx
30 - 45 Gy in 10 - 15 Fx (palliative)
184
Per TG 56, what is the tolerance for seed activity measured vs manufacturer?
Mean activity of QA seed batch vs manufacturer
* 3% or more should be investigated
* 5% or more should be reported to manufacturer
Individual seeds
* Maximum deviation in activity of 5% from the mean activity of the QA batch
185
Approximately what percentage of patients experience loose prostate seed migration to the lung? What about seed loss through the urethra or bladder?
25% of implant patients experience loose seeds that migrate to lung
9% loss through urethra/bladder
186
Given a loss of 1,2 or 3 seeds, that impact does it have on reducing D90 and V100 to the prostate?
2%, 5%, 7% reduction (assuming they were lost very soon after implantation. The more time it takes for them to migrate, the lesser the impact)
**Note:** although there is a measurable difference in target coverage, the affect on TCP is estimated to be very minimal
187
What is the approximate attenuation of modern carbon fiber couch tops at depth?
3% on average
Although certain portions ofthe device can attenuate 15% or more
188
Which TG report gives recommendations on dosimetric impact of immobilization devices?
TG 176
189
What is the approximate lifetime (beam on time) of a magnetron? What about klystron?
Magnetron: 2,000 hrs
Klystron: 10,000 hrs
190
What is the equation for leakage radiation transmission factor?
B = 1000Pd^2 / WT
U = 1
Leakage is held to 0.1% of prescription dose, hence the 1000 factor you see
191
For MR Linac, approximately how long does a treatment take from the time the initial image registration for online adaptive take, for both ATP and ATS?
ATP: 10 - 12 mins
ATS: 25 mins
192
On average, how long do MR LInac cases last (3D, IMRT, SBRT)? How many patients per day is a full day?
3D: 25 - 30 mins
Standard Fx IMRT: 35 - 40 mins
SBRT: 45 - 60 mins
Approx 10 patients per day is a full day
193
What is the average energy of the beta particles emitted by I-131?
180 keV
194
What is typical prescription activity for I-131? How is it administered?
30 - 300 mCi orally
Either pill or liquid
195
What is the release criteria based on exposure level for I-131?
7 mrem/hr at 1 meter
196
What is the half-life of Y90? What kind of radiation does it emit?
Pure beta emitter
64.2 hour half life
197
Per criteria #3 in NRC 8.39 (release via specific calculation), what is the maximum exposure rate at 1 meter for lutathera and pluvicto release?
2.1 mrem/hr
198
Above what expected exposure to any one person value would a patient given unsealed source therapy need to be given written instructions upon release?
Above 1 mSv
199
How often must DOT hazmat training be done?
Every 3 years
200
What is the max beta energy from Lu-177? What about max gamma energy?
Beta: 497 keV max
Gamma: 208 keV max
201
Approximately how long does it take lutathera to be administered?
A few hours from first amino acids, to lutathera (for approx an hour), to then 2 hours of amino acids, and time for urination
202
Per TG 76, above what expected motion is motion management needed?
5 mm
203
For photon beams, what is typical Ppol for our farmer chamber?
+- 0.06%
Very low... very close to zero. All of them are positive, but barely.
204
For photon beams, what is typical Pion for our farmer chamber? How does it change with energy?
For flattened beams, Pion is around 1.004 - 1.007. Increases with increasing energy
For FFF beams, Pion is around 1.007 - 1.015. Increases with increasing energy
205
For electron beams, is Pgr positive or negative?
In theory, it's negative. In practice, it's sometimes positive
Numerator is deeper, so in theory if you're beyond dmax to begin with, the numerator should be slightly smaller than the denominator. In practice, dref is so close to dmax, especially for lower energies, that it's uncertain whether deeper will measure higher or lower, cause you don't know exactly where on the plateu you are. So for 6E and 9E, we sometimes see positive, for 12E onwards it's typically negative
206
Is the magnitude of Pgr greater or smaller for higher electron energies?
Greater above 12E relative to 9E and below
Reason being is because dref is a bit further from the plateau, so dose gradient is more dramatic
207
For electron beams, what is our Pion? How does it vary with energy?
Around 1.3 - 1.4%
Independent of energy
208
What equation is used for shielding transmission factor of an HDR vault?
B = P(d^2)/(A x t x f x G x T)
Where A is the activity, t is the total treatment time in a given week, G is the gamma factor (R/mCi hr), and f is the exposure to dose conversion factor (for Ir-192 it's 0.96)
Essentially, the workload becomes the dose rate at 1 meter from the source derived from multiplying average curie-seconds per treatment by the number of treatments)
209
Approximately what percentage of secondary cancers resulting from radiation therapy occur...
1. Inside of the treatment field
2. Outside of the treatment field but within 5 cm of the field edge
3. More than 5 cm outside of field edges
Where are these numbers found?
1. Inside of the treatment field - 12%
2. Outside of the treatment field but within 5 cm of the field edge - 66%
3. More than 5 cm outside of field edges - 22%
Numbers are from TG 158
210
Approximately how much do OSLDs over-respond purely due to energy dependence when measuring out of field dose? What about TLDs?
OSLDs: 5 - 30% over-responsee
TLDs: 2-12% over-response
211
Per TG-158, approximately how far away from field edge do you have to go for measurement vs TPS calculation dose differences to be significant?
3 cm
212
What farmer chamber do we use for TG-51 and what is the...
Collection volume:
Radius:
Approximate calibration factor:
k=2 uncertainty on calibration certificate:
Exradin A12
Collection volume: 0.64 cc
Radius: 0.3 cm
Approximate calibration factor: 4.83 x 10^7 Gy/C
k=2 uncertainty on calibration certificate: 1.4%
213
Which TG report focuses on TSET?
TG 30
214
What is the diameter of a REM ball?
10 - 12 inches
REM ball is the bonner sphere that matches the energy used for the generalized radiation weighting factor for neutrons, so you measure effective dose.
215
Per 10 CFR 71, what is the threshold for a material to be considered "radioactive"?
If the specific activity > 0.002 uCi / g
216
Per calibration services, what is the accuracy uncertainty of our survey meters when calibrated?
+- 10%
217
How often do survey meters have to be calibrated?
Annually
218
What sources are typically used in calibration of survey meters? What about GM survey meters?
Cs-137 for survey meters
Cs-137, C-14 and Si-32 for GM survey meters
219
What is common I-131 prescription for thyroid carcinoma, and for hyperthyroidism?
Thyroid carcinoma: 120 mCi
Hyperthyroidism: 30 mCi
220
What is the SRS (single fraction) dose constraint for the brain?
V12Gy < 10 cc
221
Which TG report is on code of ethics?
TG 109
222
What is the TG report on radiochromic film dosimetry?
TG 235
223
What is the TG report on kilovoltage dosimetry?
TG 61
224
What is the TG report on small field dosimetry?
TG 155
225
What is the TG report on in-vivo diode dosimetry?
TG 62
226
What is the TG report on MLC designs?
TG 50
227
What is the TG report on IMRT commissioning?
TG 119
228
What is the TG report on image registration and fusion?
TG 132
229
What is the TG report on surface guided radiotherapy?
TG 302
230
What is the TG report on accelerator beam data commissioning?
TG 106
231
What is the TG report on hip prostheses?
TG 63
232
What is the TG report on TPS QA?
TG 53
233
What is the TG report on respiratory motion management?
TG 76
234
What is the TG report on MU verification?
TG 114
235
What is the TG report on doses outside of treated volumes?
TG 158
236
What is the TG report on use of biological models for TP?
TG 166
237
What is the TG report on dosimetric effects of couch tops?
TG 176
238
What is the TG report on monte carlo based treatment planning algorithms?
TG 105
239
What is the TG report on fetal dose effects?
TG 36
240
What is the TG report on on model based dose calculations in brachytherapy?
TG 186
241
What is the TG report on HDR treatment delivery?
TG 59
242
What is the TG report on dose prescription and reporting for prostate seed implants?
TG 137
243
What is the TG report on IMRT dosimetry?
TG 120
244
What is the TG report on IMRT QA?
TG 218
245
What is the TG report on risk analysis methods?
TG 100
246
What is the TG report on QA of nonradiographic localization and positioning systems?
TG 147
247
What is the TG report on independent MU verification for IMRT?
TG 219
248
What is the TG report on QA of CT based IGRT systems? What about dose?
TG 179 for QA
TG 180 for dose
249
What is the TG report on prostate seed ultrasound QA?
TG 128
250
What are the approximate uncertainties for diodes due to...
Dose rate per pulse (SSD)
Temperature
Angular
Field size
Dose rate per pulse (SSD): 1%
Temperature: 0.5% per centigrade (leakage increases with temperature)
Angular: Diode dependent, but around 3-4%
Field size: 5%
251
Which TG report focuses on TLDs and OSLDs?
TG 191
252
Per TG-191, what is the IROC and IAEA quoted 1 sigma uncertainty for OSLDs and TLDs?
1.6% for OSLD
2.3% for TLD
Double that to get 2 sigma
253
Approximately what percentage over-response do you expect for out of field TLDs and OSLDs from a 6 MV beam?
TLDs: 4-12%
OSLDs: 10-25%
(these numbers are purely from energy dependence. It doesn't include the nearly 5x over-resonse due to the build down effect)
254
Out of field, approximately how much do TLDs over-respond due to neutron contamination?
Factor of 10
So for out of field measurements of photon beams > 10 MV, either use OSLDs or TLDs that are insensitive to neutrons
255
How many times should OSLDs be read for a single measurement per TG-191?
At least 3 times, average out all 3 readouts
256
Per TG 178, what is the tolerance for gamma knife coincidence between radiation focal point (RFP) and unit center point (UCP)? How often should it be QA'd?
0.2 mm
QA on days of treatment per TG report
Required monthly per license
257
What are the available collimator sizes in the GK Icon?
4, 8, 16 mm
258
What is the range of a 250 MeV in water?
38 cm
259
For a 1.5 T MRI scanner, what the is approximate geometric distortion due to fluctuations of gradient field near the center of the stereotactic space?
What about near the edge (near headframe base for example)
< 0.5 mm near center
about 2 mm near headframe base
260
What is 1 Fx brainstem max dose constraint? What about optic chiasm?
Brainstem: Dmax < 15 Gy
Optic Chiasm: Dmax < 12 Gy
261
What is the 5 Fx brainstem max dose constraint?
Dmax < 31 Gy
262
What is the Brain-GTV constraint for 5 Fx SRT?
V28.8 Gy < 7 cc
263
What is an SRS cone made of, approximately how long is it?
Made of cerrobend lead encased in stainless steel
Approximately 15 cm long
264
Which TG report covers Cyberknife QA?
TG-135
265
What CTV to PTV margin is given for framed GammaKnife?
0 mm
266
What is the sensitive volume of the W1 detector?
< 2.3 mm3
267
What is the maximum magnitude that the chamber specific correction factor is allowed to exhibit for a given field size?
5%
268
What is the general spread of calculated uncertainty for correction factors in TRS 483?
For small field sizes uncertainties can reach 2-3%
As field size increases, uncertainties decrease to about 0.5%
269
For Eclipse, down to what field sizes do the models take for in and cross plane profiles? What about depth dose curves?
In and cross plane: 3x3 cm2
depth dose: 1x1 cm2
270
Which TG report gives recommendations on surface brachytherapy?
TG 253
271
Which NRC chapter is on safety during receiving of RAM?
10 CFR 20
You'd think it was 10 CFR 71, but it's not
272
What are the criteria for White I, Yellow II and Yellow III labels? What happens if Yellow III is exceeded?
White I:
* Max dose rate at surface does not exceed 0.5 mrem/hr
* Dose rate at 1 meter is effectively background
Yellow II:
* max dose rate at surface does not exceed 50 mrem/hr
* Dose rate at 1 meter is < 1 mrem/hr
Yellow III:
* Max dose rate at surface exceeds 50 mrem/hr but is less than 200 mrem/hr
* OR, dose rate at 1 meter > 1 mrem/hr but < 10 mrem/hr
If Yellow III is exceeded, package must be shipped under "exclusive use" provisions, as denoted in 49 CFR 173
273
Which TG report provides recommendations for QA, and additional general information on implementing MR in radiotherapy or in diagnostic but to be used with radiotherapy?
TG 284
