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Rad Physics > Topic 9 - Advanced Treatment Planning > Flashcards

Topic 9 - Advanced Treatment Planning Flashcards

1
Q

1 kB = ? bytes
1 MB =
1 GB =

A

2^10 or 1024 bytes
2^20
2^30

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2
Q

x-bit gray scale provides ___ unique shades

A

2^x

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3
Q

1 HU = ?% difference with respect to water

A

0.1%

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4
Q

HU of
Air
Water
Dense Bone

A

Air: -1000
Water: 0
Bone: 1300-1600

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5
Q

Higher T (field strength) MRIs do what to the acquisition time and signal noise ratio?

A

shorter acquisition

higher signal to noise ratio

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6
Q

Ultrasound equation

A

Vλ=cs where cs is the speed of sound in soft tissue 1540 ms-1
Typical frequency is 1-20 MHz; wavelength should be smaller than object in order to be reflected

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7
Q

18-FDG - half life

A

110 minutes; positron decay

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8
Q

Single kV portal film dose

A

.1-.5 mGy

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9
Q

CBCT dose

A

1-5 cGy

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10
Q

Block Edge =

A

PTV + Penumbra

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11
Q

irradiated volume

A

=Volume enclosed by the 50% isodose surface

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12
Q

Treated volume

A

=Volume enclosed by the 95% isodose surface (generally 2 cm margin between PTV and field edge

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13
Q

MUs for 3D vs IMRT

A

You need generally 2x the MUs for IMRT (and 10x for tomotherapy!)

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14
Q

MUs for VMAT vs IMRT

A

fewer MUs in VMAT

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15
Q

Low energy beam advantages

A

lower whole body dose, less buildup for superficial tumors, lower exit dose

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16
Q

in IMRT QA, with indivirual beam measurment what are the thresholds to pass?

A

if within 3% of dose or within 3 mm from point of agreement

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17
Q

disadvantages of IMRT

A 
2x treatment time 
greater dependence on setup uncertainty
more inhomogeneity
more whole body dose (2-3x)
greater room shielding requirements
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18
Q

positional accuracy of SRS

A

+/- 1 mm

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19
Q

Cyberknife technology (beam energy and creation, patient movement)

A

6 MV linac on robotic arm, frameless
uses X-band microwaves (10,000 MHz) compared to linacs (3000 MHz)
patient position monitored continuously with orthogonal X-ray beams and can track moving target volumes

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20
Q

Gamma-knife (Source, arrangement, pt movement, prescribtion)

A

200 Co-60 sources with a total activity of 60,000 Ci (220 Bq)
arranged in hemispheric chell of r= 40 cm
final collimation with bolted helmet
multiple isocenters
prescribe to the 50% dose line

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21
Q

Linac-bases SRS/SBRT (isocenters, MLCs, prescription)

A

usually a small number of isocenters (sometimes 1)
Mini or micro MLCs (3-4 mm leaf width)
prescribe to the 80-90% dose line

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22
Q

conformality index measures what? Acceptable range?

A

prescription isodose to target volume (PITV) is a measure of conformality
ranges 1-2 are acceptable 2-2.5 or 0.9-1 are minor deviations

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23
Q

How are beam profiles measured for srs/sbrt?

A

With film due to high spatial resolution

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24
Q

How is PDD, TMR, Sc,p measured for SRS/SBRT?

A

Small ion chambers <3mm

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25
Winston Lutz Test
determines target accuracy radiate small metallic ball and compare the difference between the center of the sphere shadow and the center of the field
26
proton SAD difference
Very high SADs (200 cm)
27
Proton dose depth vs photons
is increased compared to photons due to inverse square fall off of dose with distance
28
Therapeutic energy rance of protons
30*250 MeV
29
Protons are ____ susceptible to tissue heterogeneity than photons
More
30
How often are the outputs for the SOBP and distal dose fall off measured for proton therapy?
Daily
31
TSEB therapy beam energy
2-9 MeV
32
Hyperthermia target temperature
41-45 degrees C over 30-60 minutes
33
Thermal enhancement ratio
RT dose without heat/RT dose for equivalent effect with heat
34
In IMRT optimization, "cost" quantifies ____.
The deviation from the desired dose distribution.
35
Pencil beam convolution can be used to ___.
perform dose calculations for IMRT.
36
beam spoiler in TBI is used to ___.
Increase surface dose in the skin's blood vessels This is also called a bolus! It is a 1-2 cm acrylic screen placed as close to the patient as possible. Most protocols don't require skin sparing
37
The range of uncertainty in proton beams is approximately ___ the range of the beam.
2.5-4%
38
Proton range straggling is caused by uncertainties in ___.
Energy Loss. The sigmoidal shape at the distal end of the bragg peak is due to range straggling which is caused by small statistical fluctuation in the amount of E lost by individual protons.
39
Range uncertainty in protons
Due to uncertainties in tissue composition and stopping power.
40
Higher energy photon beams have _____ penumbra.
Increased
41
prescribing to the 50-80% isodose lines in SRS is done in order to minimize ____.
Normal tissue exposure. You are prescribing into the penumbra. This introduces hotspots but will minimize normal tissue exposure.
42
Benefits of MLC for SRS
no shape limitations for single isocenter | more flexibility in technique (static, dynamic conformal arc, IMRT, VMAT)
43
Benefit of cones over MLC for SRS
Sharper penumbra as it is shaped closer to the patients head
44
What is the frequency and tolerance to verify mechanical vs. imaging system iso on modern linacs?
daily; = 2.0 mm
45
Can a linac accelerate protons?
Yes, but it takes greater lengths of the cavity.
46
What is the function of a degrader in TSET?
To decrease the depth of e- beam penetration.
47
What is a greater concern for PBS vs passive scatter?
Target motion
48
Gating should be considered if target motion in any one direction is ____.
> 5mm
49
____ cannot be ionized for use in particle therapy.
Neutrons (because they are neutral).
50
QA tolerance of couch translation and rotation for SRS/SBRT vs non-IMRT?
1 mm; 0.5 degrees - SRS/SBRT | 2 mm, 1 mm for non-IMRT
51
QA frequency of door safety
daily
52
QA frequency of audio/visual monitors
daily
53
QA frequency of X-ray output consistancy of within 3%
daily
54
QA frequency of distance indicator at iso within 2mm
daily
55
QA frequency of "picket fence' test for MLC positioning
Weekly
56
What are medical events reportable to the NRC?
``` Wrong body site Wrong modality (15x vs 6x) Any one fraction>50%, or total dose exceeding 20% ```
57
What are good moderators of neutron energy?
Polyethylene, water, concrete -- materials with a lot of hydrogen. They slow down neutrons because the protons in the material have a similar mass as the incident neutrons allowing efficient energy transfer.
58
QA frequency of kV to MV isocenters?
daily
59
kV imaging deposits most of the dose where?
at the surface
60
What is the MIP in a 4D CT?
CT dataset where each individual pixel is assigned to its maximum value from all breathing phases
61
Why is the collimator sometimes rotated for VMAT?
Dose banding from interleaf leakage can be reduced by rotating the gantry.
62
Advantages of VMAT over IMRT
shorter treatment time (and thus decreased intrafractional movement) (dose rate is the same or less than IMRT)
63
physical compensators do what in TBI?
increase homogeneity. They attenuate the beam decreasing the dose rate to compensate for the varying separations of the body.
64
TBI dose agreement and dose uniformity?
5% and 10%
65
DIBH reduces the dose to the
heart and lungs
66
The LET for protons is highest where?
At the distal end of the SOBP
67
Passively scattered protons create out of field dose with _____.
Neutrons. Passively scattered proton beam interacts with the aperture and the nozzle creating neutrons and gammas.

Rad Physics (4 decks)

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