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abr part 3 > Numbers to memorize > Flashcards

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

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2
Q

Above what whole body dose is there a nearly 100% lethality?

A

6 Gy

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3
Q

What voltages is the GM region in?

A

1000 - 1400 V

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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)

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5
Q

What is the typical axial resolution of an ultrasound?

A

0.5 mm

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6
Q

Per TG-128, what is the tolerance for depth of penetration test?

A

1 cm

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7
Q

What is the NCRP 147 exposure in any one hour limit?

A

0.02 mSv in any one hour

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8
Q

What is a typical DLP for helical CT?

A

Hundreds of mGy*cm

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9
Q

What is a typicaly CTDI for helical CT?

A

20 - 80 mGy

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10
Q

Which TG report outlines QA for gamma knife?

A

TG 148

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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

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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

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13
Q

Which TG report gives guidance on PET/CT shielding?

A

TG 108

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14
Q

What is the half-life of F-18?

A

110 mins

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15
Q

How far do emitted positrons of F-18 travel before annihilation on average?

A

1 - 2 mm

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16
Q

What is the resolution in a typical PET scanner?

A

6 - 10 mm

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17
Q

Typical dose to patients from a PET/CT

A

25 mSv per scan

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18
Q

What is the typical shielding in inches of lead of a CT sim?

A

1/16” lead

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19
Q

What is the typical shielding of a PET/CT suite?

A

1-2 cm of lead

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20
Q

What is the typical shielding of an HDR suite?

A

50 cm of concrete

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21
Q

What is the typical shielding of Co-60 suite?

A

70 cm of concrete

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22
Q

Which TG report focuses on QA of TPS and when did it come out?

A

TG-53

1998

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23
Q

What is the half-life of I-131?

A

8 days

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24
Q

What is the dose range of EBT 3 Film?

A

0.2 Gy to 10 Gy

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25
Q

What is the shielding for a Linac vault?

A

Primary barrier: 2 - 3 m of concrete
Secondary barrier: 1.5ish m of concrete

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26
Q

What is typical shielding for a Cyberknife vault?

A

170 cm of concrete

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27
Q

What is a typical Pion value for farmer chambers for…

Flat photon beams
FFF photon beams
Electron beams

A

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

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28
Q

What is the acceptable dose to radiation workers and general public and why are these numbers different?

A

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

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29
Q

How thick is the lead foil used in TG-51, and how far from water surface do we keep the foil?

A

1 mm thick lead foil

30 cm from water surface used due to clearance issues (50 cm not achievable)

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30
Q

What are some typical collection volumes for…

Farmer chambers
Scanning ion chambers
Microchambers

A

Farmer chambers: ~0.6 cc
Scanning ion chambers: ~0.1 cc
Microchambers: ~0.01 cc

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31
Q

What is approximate bremsstrahlung contamination relative to Dmax for 4 MeV to 20 MeV beams?

A

~1% for 4 MeV
~4% for 20 MeV

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32
Q

How many prostate seeds are placed in a patient?

A

Around 50 - 120 seeds

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33
Q

How wide is a typical prestine bragg peak for proton beams and what influences the width?

A

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
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34
Q

What is typical prescription in H&N?

A

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

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35
Q

For H&N treatments, what is the go to dose constraint resource typically. And what are the constraints for…

Cord
Brainstem
Parotid
Mandible
Esophagus

A

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

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36
Q

What are the standard occupational dose limits for adults as outlined by 10 CFR 20?

A

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

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37
Q

What is the efficiency range of MV photon beam bremmstrahlung production of Linac targets per Khan?

A

30 - 95%

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38
Q

What are typical transmisison factors through…
Primary collimator
jaws
MLCs?

A

Primary collimators: 0.1%
Jaws: <2%, in practice around 0.5%
MLCs: <5%, in practice around 1-2%

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39
Q

What is the rule of thumb for out of field dose at 10 cm and 30 cm from photon field edge?

A

10 cm: 1% of CAX
30 cm: 0.2% of CAX

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40
Q

Per TG 36, at what dose level does risk to fetus become “significant?”

A

0.1 - 0.5 Gy during the first trimester

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41
Q

Which NCRP report contains a table of tissue weighting factors for effective dose equivalent? What tissue has the highest factor?

A

NCRP 116 contains the table

Gonads has the highest factor at 0.2

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42
Q

At what threshold dose does GI acute syndrome occur?

A

6 Gy total body dose

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43
Q

Per NRC regulatory guide 8.29, what is the estimated loss of life expectancy for a radiation worker? What is responsible for this loss?

A

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

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44
Q

What is the approximate fade of TLDs over the course of a month?

A

Approx 1%/month fade

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45
Q

Per TG-51 addendum, what are the criteria for a ion chamber to be classified as a reference class ion chamber?

A

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%

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46
Q

What TG report gives recommendations on the QM of EBRT data transfer?

A

TG 201

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47
Q

What are the Dmax constraints for spinal cord for 1, 3 and 5 Fx SBRT per TG 101?

A

1 Fx: Dmax < 14 Gy
3 Fx: Dmax < 21.9 Gy
5 Fx: Dmax < 30 Gy

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48
Q

What is the energy of F-18 emitted positron and approximately how far will it travel before annihilation?

A

On average 0.63 MeV

Will travel mean distance of 2.4 mm before annihilation

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49
Q

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?

A

2x2 cm2 field: approx 0.8
0.5 x 0.5 cm2 field: approx 0.4

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50
Q

What are typical dose rate constants for common HDR sources? How do you determine it?

A

Constants are published by TG-43U1 and TG-43

Typical values are around 1 - 1.1 cGy / hr U

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51
Q

When was NJ set as an agreement state?

A

2009

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52
Q

What is the limit of AAPM gift from vendor? Can this be exceeded? What if a vendor takes you to dinner?

A

$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

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53
Q

What three survey meters do we have in our department?

A

Victoreen 450A and 450B
Ludlum 3

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54
Q

Which article containts most NJ state regs?

A

NJAC Title 7 Ch 28

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55
Q

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?

A

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

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56
Q

How does the depth of dref compare with dmax?

A

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

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57
Q

What is the approximate error in PDD(dref) if you forget to convert from I50 to R50?

A

Approximately 3 - 5% error

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58
Q

Per TG 40, what is HDR source timer accuracy requirement?

A

1%

So if 100 seconds is used, tolerance is 1 second

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59
Q

What is the relative accuracy of a geiger counter? What is the device typically used for?

A

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

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60
Q

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?

A

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

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61
Q

What diseases are typically treated using TBI, and what are the prescriptions?

A

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

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62
Q

What is typical volume, length and radius of a farmer chamber? What is the wall typically made of? What baout central electrode?

A

Volume: 0.6 cc
Length: 2.3 cm
Radius: 3 mm
Wall is typically graphite and plastic
Central electrode is typically aluminum

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63
Q

Where is EPOM for your farmer chamber for photons and electrons?

A

0.18cm upstream for photons
0.15cm upstream for electrons

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64
Q

What is typically being treated in CSI and what is a typical prescription? How effective is it?

A

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

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65
Q

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?

A

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)

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66
Q

What is the energy of BPE neutron capture gammas?

A

0.48 MeV from boron component (most common)
2.2 MeV from hydrogen

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67
Q

What is the the neutron TVL for BPE?

A

4.5 cm

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68
Q

What are typical concrete thicknesses for primary and secondary barriers in a high energy LINAC vault? What about door thickness with and without maze?

A

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

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69
Q

Per NCRP 151, what occupancy factor is used for corridors? What about vault door? What about stairways?

A

Corridors: 1/5
Vault door: 1/8
Stairways: 1/40

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70
Q

What is the use factor of barriers 2 and 3?

A

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

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71
Q

How much of a dose shadow do you expect to see for diodes? What is, reduction of skin dose?

A

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

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72
Q

What is tenth-value distance in linac vault shielding? How long is a typical TVD? What factors impact it?

A

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)

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73
Q

By about what factor do proton plans reduce integral dose relative to IMRT/VMAT and 3D plans?

A

2-3x less integral dose than IMRT/VMAT
2-7x less integral dose than 3D plans

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74
Q

What is Bremsstrahlung energy efficiency for…
Superficial therapy units
Orthovoltage therapy
MV therapy

A

Superficial: 0.5%
Orthovotlage: 2%
MV: 30% and higher

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75
Q

What are the common kV therapy energy ranges? What are some applications?

A

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

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76
Q

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?

A

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

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77
Q

Which TG report gives recommendations on QA of CT based IGRT systems?

A

TG 179

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78
Q

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

A

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

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79
Q

What is the cited accuracy of the Luxel+ OSLD badge you have?

A

+- 15%

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80
Q

What is the approximate reduction in barometric pressure vs altitude? What altitude do local airports provide barometric pressure at?

A

1 in Hg per 1000 Ft of altitude

Local airports typically provide pressure relative to sea level

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81
Q

As shown in TG-51, what is the spread in Kq values for given Q among different ion chambers?

A

1.5ish% spread

That is, all ion chambers have a kQ value for a given Q within 1.5% of one another

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82
Q

For Varian Linacs, how does photoneutron production increase as you go from 15 MV to 18 MV beams?

A

Increases by approx 60%

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83
Q

What is approximate primary beam thickness in concrete for two adjacent 18 MV vaults?

A

Approximately 2 m

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84
Q

Per 10 CFR 20, what is the total effective dose limit to members of the public?

A

1 mSv/yr
0.02 mSv in any one hour in an uncontrolled area
5 mSv/yr for visitors

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85
Q

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?

A

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)

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86
Q

Per TG-36, at what dose level does risk to fetus become significant?

A

10 - 50 cGy

At around 100 cGy there is a 50% risk of malformation

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87
Q

What is approximate surface dose for…

Co-60
6MV
10MV
18MV

A

Co-60: 50%
6MV: 25%
10MV: 23%
18MV: 20%

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88
Q

What is the Roentgen to rad conversion factor (MV beam) for air? What about tissue?

A

Air: 0.876 cGy/R
Tissue: 0.97 cGy/R

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89
Q

What are our clinical TMR for a 10x10 cm2 field for…

6MV
6FFF
10MV
10FFF
15MV

A

6MV - 77.4%
6FFF - 73.9%
10MV - 84.3%
10FFF - 81.3%
15MV - 87.1%

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90
Q

What are our Edge commissioned R50 for a 10x10cm2 cone for…

6E
9E
12E
16E
20E

A

6E - 2.36 cm
9E - 3.58 cm
12E - 5.00 cm
16E - 6.64 cm
20E - 8.27 cm

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91
Q

What is the approximate pdd(10) for a 6MV beam? What is it in our clinic?

A

65-67%

In our clinic it’s 66.9%

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92
Q

What is the approximate pdd(10) for a 6FFF beam?

A

63-64%

In our clinic it’s 63.7%

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93
Q

What is the approximate pdd(10) for a 10MV beam?

A

73-75%

In our clinic it’s 74.1%

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94
Q

What is the approximate pdd(10) for a 10FFF beam?

A

70-72%

In our clinic it’s 71.1%

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95
Q

What is the approximate pdd(10) for a 15MV beam?

A

76-77%

In our clinic it’s 77%

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96
Q

What is the approximate pdd(10) for a 18MV beam?

A

80%

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97
Q

What is the approximate dmax for a 6FFF beam?

A

1.4 - 1.5 cm

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98
Q

What is the approximate dmax for a 6MV beam?

A

1.4 - 1.5 cm

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99
Q

What is the approximate dmax for a 10FFF beam?

A

2.2 - 2.4 cm

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100
Q

What is the approximate dmax for a 10MV beam?

A

2.2 - 2.4 cm

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101
Q

What is the approximate dmax for a 15MV beam?

A

2.7 - 2.9 cm

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102
Q

What is the approximate dmax for a 18MV beam?

A

3.3 cm

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103
Q

What is the approximate pdd(10) for a Co-60 beam?

A

55%

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104
Q

If given E0, what is the approximate R80 in water? What about R90?

A

R80(cm) = E0/2.8
R90(cm) = E0/3.2

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105
Q

What is approximate dmax of a 6E beam?

A

1.2 - 1.3 cm

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106
Q

What is approximate dmax of a 9E beam?

A

1.9 - 2.1 cm

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107
Q

What is approximate dmax of a 12E beam?

A

2.8 - 2.9 cm

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108
Q

What is approximate dmax of a 16E beam?

A

3.0 - 3.1 cm

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109
Q

What is approximate dmax of a 20E beam?

A

2.5 cm

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110
Q

What is the approximate surface dose for electrons with energies between 6E and 20E, and how does it change with increasing energy?

A

78 - 95%

Increases with increasing energy

111
Q

What is the approximate HU of fat?

A

-80

112
Q

What is the approximate HU of CSF?

A

15

113
Q

What is the approximate HU of blood and muscle?

A

40

114
Q

What is the approximate Z of tissue?

A

7.4

115
Q

What is the approximate Z of bone?

A

14

116
Q

What is the approximate density of lead?

A

11.34 g/cc

117
Q

What is the approximate density of tungsten?

A

19.25 g/cc

118
Q

What typically classifies a teletherapy medical event in a state?

A
  • Wrong patient or site
  • Total dose differs by 20% (for treatments >3fx)
  • Total dose differs by 10% (for treatments <= 3fx)
119
Q

What is the quoted proton radiation weighting factor per 10 CFR 20?

A

10

120
Q

What is the half-life of Co-60?

A

5.3 years

121
Q

What is the half-life of Ir-192?

A

73.83 days

122
Q

What is the half-life of I-125?

A

59.6 days

123
Q

What is the half-life of Lu-177?

A

6.7 days

124
Q

What is typical Z of a prostheses?

A

20 - 25

125
Q

What is approxiate TVL for 6X and 18X in concrete?

A

6X - 37 cm
18X - 45 cm

126
Q

At what skin acute exposure levels do you get…

Erythema
Wet Desquamation
radionecrosis

A

Erythema - 6 Sv
Wet Desquamation - 25 Sv
radionecrosis - 50 Sv

127
Q

What is the risk for developing cancer over lifespan due to 100 mSv, compared to that of all other causes?

A

1% for radiation 100 mSv
42% for all other causes

128
Q

What tissue has the highest tissue weighting factor? What about the lowest?

A

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
Q

Approximately how much of the electron kinetic energy is converted to microwave energy in a magnetron?

A

60%

130
Q

What is typical radiation offset for MLCs?

A

0.4 - 1.1 mm

131
Q

What is relative electron density of bone? What about dense bone?

A

Bone: 1.2ish
Dense bone: 1.8ish

132
Q

Below what dose value is there no clear scientific evidence of any adverse health effects at chronic radiation doses?

A

Below 100 mSv

133
Q

What dose rates characterize HDR? Where is the dose rate specified?

A

12 Gy/hr at prescription point
or 0.2 Gy/min

134
Q

What dose rates characterize LDR? Where is the dose rate specified?

A

0.4 - 2 Gy/hr at prescription point

135
Q

What is the average photon energy of Cs-137?

A

662 keV

136
Q

What is the average photon energy of I-125?

A

28 keV

137
Q

For T&O HDR, what is the culumative (EBRT+HDR) EQD2 constraint for…

Rectum
Bowel
Sigmoid
Bladder

A

Rectum: D2cc < 75 Gy
Bowel: D2cc < 75 Gy
Sigmoid: D2cc < 75 Gy
Bladder: D2cc < 90 Gy

138
Q

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?

A

0.75 Gy

139
Q

Up to what distance away from a Ir-192 source does inverse square effects dominate?

A

4 cm

140
Q

What is the NRC limit on leakage levels for HDR afterloader units?

A

1 mR/hr at 10 cm from any surface of the afterloader

141
Q

What are the requirements for White I, Yellow II and Yellow III labels?

A

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
Q

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?

A

120 days

(remember it as 2x half like of I-125)

143
Q

What is the typical density of concrete?

A

2.35 g/cc

144
Q

Per 10 CFR 20, what defines a radiation area?

A

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
Q

Per 10 CFR 20, what defines a high radiation area?

A

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
Q

Per 10 CFR 20, what defines a very high radiation area?

A

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
Q

Per NRC, what is the approximate risk of fatal cancer from radiation exposure per rem?

A

1 / 2500 chance of fatal exposure per rem (10 mSv) of TEDE received

NRC Regulatory Guide 8.29

148
Q

Assuming you get 10 mSv of exposure per year, what is the expected lost life expectancy and how does this compare to other industries?

A

51 days lost life expenctancy

The average across all industries is 60 days lost life expenctancy, so we’re below average

149
Q

What is the lot to lot variation of radiochromic film calibration?

A

+- 5% variation

150
Q

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?

A

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
Q

For APBI using balloon applicatory, what is the minimum distance of balloon surface to skin surface, and what is the maximum allowed skin dose?

A

Min distance is 7mm

Max allowed skin dose is 145% of prescription dose

152
Q

What is the duty cycle of a Linac?

A

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
Q

Approximate how much larger is photon mode current than electron mode current in a Linac?

A

100x

Photon mode is approximately 100 mA/pulse
Electron mode is approximately 1 mA/pulse

154
Q

What is typical prescription for CSI?

A

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
Q

How often does a Varian MLC log file record MLC leaf positions?

A

Every 50 ms

156
Q

What is te approximate coincidence time window used in PET imaging?

A

10 - 20 ns

157
Q

How does neutron dose rate increase when you fully shut jaws (relative to open field)

A

Increases by about 75%

158
Q

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?

A

1 Gy photons at isocenter is approximately 1 uSv neutron dose equivalent at outer maze entrance

159
Q

What is the typical dosimetric penumbra from MLCs?

A

4 - 7 mm

160
Q

What is typical shielding for HDR in concrete and lead?

A

50 cm of concrete
5 cm of lead

161
Q

By about how much can diode perturbation affect dose at 5 cm depth?

A

< 5% for correctly used diode energy
up to 10% for high energy diode used in low energy beam

162
Q

What is the half-life of Pd-103?

A

17 days

163
Q

What is the half-life of Cs-131?

A

9.7 days

164
Q

What is the diameter of cyclotrons used in proton therapy?

A

3.5 - 5 meters

165
Q

What is the diameter of synchrotrons used in proton therapy?

A

8 - 10 meters

166
Q

What is the approximate range of correction factor for solid water to liquid water? That is…

CF = reading in water / reading in solid water

A

+- 1%

Usually CF > 1.000 for electrons and < 1.000 for photons

167
Q

What is LDR prostate dose for Pd-103 and I-125, monotherapy?

A

Pd-103: 125 Gy
I-125: 145 Gy

168
Q

What is the average size of a prostate? What is the average size of a prostate in patients with prostate cancer?

A

Average size of healthy prostate = 25 cc
Average size of prostate cancer prostate = 50 cc

169
Q

For Pd 103 and I-125, what is the model calculated best time to perform prostate seed post plan?

A

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
Q

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?

A

Simple geomtries: 2%
Small fields or low density heterogeneities: 5%

171
Q

What tolerance do we use for flatness and symmetry annually? What is baseline?

A

+- 1% from baseline

For symmetry, baseline is 0
For flatness, baseline is whatever TPS gives

172
Q

What is the air kerma rate constant for Ir-192? What about for I-125 and Pd-103?

A

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
Q

Do modern TPS algorithms have more or less trouble calculating FFF beams compared to flattened beams?

A

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
Q

For FFF vs flattened beams, which will result in better portal dosimetry imaging (assuming correction for dose profile done in service mode)

A

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
Q

Besides gamma analysis, what are some other methods that can be used to compare two different dose distributions?

A
  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
Q

What is the most commonly used gamma criteria? Which TG report suggested it?

A

3% / 3 mm, 95% pass rate, global normalization, TG-119

Note: TG-119 is actually the IMRT commissioning report

177
Q

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?

A

5% within mean dose to volume

So both max and mean dose should be within +-5% of mean dose

178
Q

Which TG report gives recommendations on patient specific IMRT QA? What is the recommended gamma criteria from this report?

A

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
Q

What are layers and thicknesses of layers for a direct shielded door used for a high energy linac vault?

A

0.25” steel casing
3” lead
11” of 5% BPE
3” lead
0.25” steel casing

180
Q

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?

A

Neutrons: 62%
Leakage: 30%
Neutron capture gamma rays: 8%

181
Q

What ‘a’ values are used in gEUD calculations for…

Target, Parallel organs and serial organs?

A

Target: a = -10
Parallel organs: a = 1
Serial organs: a = 10 - 20

182
Q

For conventional fractionation, what is the most common total lung constraint?

A

V20Gy <= 30% of total lung

183
Q

What are some common lung fractionations?

A

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
Q

Per TG 56, what is the tolerance for seed activity measured vs manufacturer?

A

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
Q

Approximately what percentage of patients experience loose prostate seed migration to the lung? What about seed loss through the urethra or bladder?

A

25% of implant patients experience loose seeds that migrate to lung
9% loss through urethra/bladder

186
Q

Given a loss of 1,2 or 3 seeds, that impact does it have on reducing D90 and V100 to the prostate?

A

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
Q

What is the approximate attenuation of modern carbon fiber couch tops at depth?

A

3% on average

Although certain portions ofthe device can attenuate 15% or more

188
Q

Which TG report gives recommendations on dosimetric impact of immobilization devices?

A

TG 176

189
Q

What is the approximate lifetime (beam on time) of a magnetron? What about klystron?

A

Magnetron: 2,000 hrs
Klystron: 10,000 hrs

190
Q

What is the equation for leakage radiation transmission factor?

A

B = 1000Pd^2 / WT

U = 1
Leakage is held to 0.1% of prescription dose, hence the 1000 factor you see

191
Q

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?

A

ATP: 10 - 12 mins
ATS: 25 mins

192
Q

On average, how long do MR LInac cases last (3D, IMRT, SBRT)? How many patients per day is a full day?

A

3D: 25 - 30 mins
Standard Fx IMRT: 35 - 40 mins
SBRT: 45 - 60 mins

Approx 10 patients per day is a full day

193
Q

What is the average energy of the beta particles emitted by I-131?

A

180 keV

194
Q

What is typical prescription activity for I-131? How is it administered?

A

30 - 300 mCi orally

Either pill or liquid

195
Q

What is the release criteria based on exposure level for I-131?

A

7 mrem/hr at 1 meter

196
Q

What is the half-life of Y90? What kind of radiation does it emit?

A

Pure beta emitter

64.2 hour half life

197
Q

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?

A

2.1 mrem/hr

198
Q

Above what expected exposure to any one person value would a patient given unsealed source therapy need to be given written instructions upon release?

A

Above 1 mSv

199
Q

How often must DOT hazmat training be done?

A

Every 3 years

200
Q

What is the max beta energy from Lu-177? What about max gamma energy?

A

Beta: 497 keV max
Gamma: 208 keV max

201
Q

Approximately how long does it take lutathera to be administered?

A

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
Q

Per TG 76, above what expected motion is motion management needed?

A

5 mm

203
Q

For photon beams, what is typical Ppol for our farmer chamber?

A

+- 0.06%

Very low… very close to zero. All of them are positive, but barely.

204
Q

For photon beams, what is typical Pion for our farmer chamber? How does it change with energy?

A

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
Q

For electron beams, is Pgr positive or negative?

A

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
Q

Is the magnitude of Pgr greater or smaller for higher electron energies?

A

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
Q

For electron beams, what is our Pion? How does it vary with energy?

A

Around 1.3 - 1.4%

Independent of energy

208
Q

What equation is used for shielding transmission factor of an HDR vault?

A

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
Q

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?

A
  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
Q

Approximately how much do OSLDs over-respond purely due to energy dependence when measuring out of field dose? What about TLDs?

A

OSLDs: 5 - 30% over-responsee
TLDs: 2-12% over-response

211
Q

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?

A

3 cm

212
Q

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:

A

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
Q

Which TG report focuses on TSET?

A

TG 30

214
Q

What is the diameter of a REM ball?

A

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
Q

Per 10 CFR 71, what is the threshold for a material to be considered “radioactive”?

A

If the specific activity > 0.002 uCi / g

216
Q

Per calibration services, what is the accuracy uncertainty of our survey meters when calibrated?

A

+- 10%

217
Q

How often do survey meters have to be calibrated?

A

Annually

218
Q

What sources are typically used in calibration of survey meters? What about GM survey meters?

A

Cs-137 for survey meters

Cs-137, C-14 and Si-32 for GM survey meters

219
Q

What is common I-131 prescription for thyroid carcinoma, and for hyperthyroidism?

A

Thyroid carcinoma: 120 mCi
Hyperthyroidism: 30 mCi

220
Q

What is the SRS (single fraction) dose constraint for the brain?

A

V12Gy < 10 cc

221
Q

Which TG report is on code of ethics?

A

TG 109

222
Q

What is the TG report on radiochromic film dosimetry?

A

TG 235

223
Q

What is the TG report on kilovoltage dosimetry?

A

TG 61

224
Q

What is the TG report on small field dosimetry?

A

TG 155

225
Q

What is the TG report on in-vivo diode dosimetry?

A

TG 62

226
Q

What is the TG report on MLC designs?

A

TG 50

227
Q

What is the TG report on IMRT commissioning?

A

TG 119

228
Q

What is the TG report on image registration and fusion?

A

TG 132

229
Q

What is the TG report on surface guided radiotherapy?

A

TG 302

230
Q

What is the TG report on accelerator beam data commissioning?

A

TG 106

231
Q

What is the TG report on hip prostheses?

A

TG 63

232
Q

What is the TG report on TPS QA?

A

TG 53

233
Q

What is the TG report on respiratory motion management?

A

TG 76

234
Q

What is the TG report on MU verification?

A

TG 114

235
Q

What is the TG report on doses outside of treated volumes?

A

TG 158

236
Q

What is the TG report on use of biological models for TP?

A

TG 166

237
Q

What is the TG report on dosimetric effects of couch tops?

A

TG 176

238
Q

What is the TG report on monte carlo based treatment planning algorithms?

A

TG 105

239
Q

What is the TG report on fetal dose effects?

A

TG 36

240
Q

What is the TG report on on model based dose calculations in brachytherapy?

A

TG 186

241
Q

What is the TG report on HDR treatment delivery?

A

TG 59

242
Q

What is the TG report on dose prescription and reporting for prostate seed implants?

A

TG 137

243
Q

What is the TG report on IMRT dosimetry?

A

TG 120

244
Q

What is the TG report on IMRT QA?

A

TG 218

245
Q

What is the TG report on risk analysis methods?

A

TG 100

246
Q

What is the TG report on QA of nonradiographic localization and positioning systems?

A

TG 147

247
Q

What is the TG report on independent MU verification for IMRT?

A

TG 219

248
Q

What is the TG report on QA of CT based IGRT systems? What about dose?

A

TG 179 for QA
TG 180 for dose

249
Q

What is the TG report on prostate seed ultrasound QA?

A

TG 128

250
Q

What are the approximate uncertainties for diodes due to…

Dose rate per pulse (SSD)
Temperature
Angular
Field size

A

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
Q

Which TG report focuses on TLDs and OSLDs?

A

TG 191

252
Q

Per TG-191, what is the IROC and IAEA quoted 1 sigma uncertainty for OSLDs and TLDs?

A

1.6% for OSLD
2.3% for TLD

Double that to get 2 sigma

253
Q

Approximately what percentage over-response do you expect for out of field TLDs and OSLDs from a 6 MV beam?

A

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
Q

Out of field, approximately how much do TLDs over-respond due to neutron contamination?

A

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
Q

How many times should OSLDs be read for a single measurement per TG-191?

A

At least 3 times, average out all 3 readouts

256
Q

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?

A

0.2 mm

QA on days of treatment per TG report
Required monthly per license

257
Q

What are the available collimator sizes in the GK Icon?

A

4, 8, 16 mm

258
Q

What is the range of a 250 MeV in water?

A

38 cm

259
Q

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)

A

< 0.5 mm near center

about 2 mm near headframe base

260
Q

What is 1 Fx brainstem max dose constraint? What about optic chiasm?

A

Brainstem: Dmax < 15 Gy
Optic Chiasm: Dmax < 12 Gy

261
Q

What is the 5 Fx brainstem max dose constraint?

A

Dmax < 31 Gy

262
Q

What is the Brain-GTV constraint for 5 Fx SRT?

A

V28.8 Gy < 7 cc

263
Q

What is an SRS cone made of, approximately how long is it?

A

Made of cerrobend lead encased in stainless steel
Approximately 15 cm long

264
Q

Which TG report covers Cyberknife QA?

A

TG-135

265
Q

What CTV to PTV margin is given for framed GammaKnife?

A

0 mm

266
Q

What is the sensitive volume of the W1 detector?

A

< 2.3 mm3

267
Q

What is the maximum magnitude that the chamber specific correction factor is allowed to exhibit for a given field size?

A

5%

268
Q

What is the general spread of calculated uncertainty for correction factors in TRS 483?

A

For small field sizes uncertainties can reach 2-3%

As field size increases, uncertainties decrease to about 0.5%

269
Q

For Eclipse, down to what field sizes do the models take for in and cross plane profiles? What about depth dose curves?

A

In and cross plane: 3x3 cm2
depth dose: 1x1 cm2

270
Q

Which TG report gives recommendations on surface brachytherapy?

A

TG 253

271
Q

Which NRC chapter is on safety during receiving of RAM?

A

10 CFR 20

You’d think it was 10 CFR 71, but it’s not

272
Q

What are the criteria for White I, Yellow II and Yellow III labels? What happens if Yellow III is exceeded?

A

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
Q

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?

A

TG 284

abr part 3 (2 decks)

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