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RAPHEX > RAPHEX III > Flashcards

RAPHEX III Flashcards

1
Q

what particle has rest mass of 938 MeV?

A

proton

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2
Q

binding energy of 69, 12, and 2 keV
possible characteristic xrays for 100 keV photon striking atom

A

57, 67, 2 keV

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3
Q

does beta minus emission contribute for Co-60?

A

No
there is beta emission but it is typically absorbed in source housing

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4
Q

is beam current higher in electron or photon mode

A

photon mode

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5
Q

cerrobend blocks have more or less primary transmission than MLC?

A

more
they can conform to any shape
*remember these are different than cones

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6
Q

what are HU linearly related to?

A

linear attenuation coefficient was right anseer
electron density was wrong- maybe because it should be relative electron density?

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7
Q

why do neutrons have higher Q factor than electrons?

A

they transfer their energy to protons, which have higher LET

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8
Q

average energy of 6 MV beam

A

about 3.8 MeV
6MeV is max

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9
Q

advantages of radiochromic vs radiographic include all the following except?
-nearly tissue equivalent
-doesn’t require post irradiation processing
-relatively insensitive to viosible light
-more linear response
-requires lower dose

A

-last one is wrong, it requires a higher dose

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10
Q

normalized to 100%, physician treats 180 cGy to 95 % isodose line, hot spot is 107%. Hot spot for 25 fractions

A

180/0.95 * 1.07
5068 cGy

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11
Q

why might physician treat with 10 MV in lung instead of 6 MV

A

lower dmax dose

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12
Q

2 blocks- one has midline block and the other a corner block. For to the right of center of field, which has a more penetrating depth dose?

A

-one woth corner block has more penetrating PDD
-midblock changes equivalent square more than corner block

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13
Q

all of the following are advantages of a dynamic wedge vs conventional except:
a)same depth dose
b)field not limited in non-wedge direction
c)therapists don’t have to lift
d) less dose outside field
e)wedge transmission factpr is independent of field width

A

e
it does depend

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14
Q

are attenuation corrections greater for 6 or 15 MV photons?

A

greater for 6 MV
but interface effects are worse at high energy

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15
Q

a wedged breast plan is calculated without heterogeneity corrections. The same plan is then corrected for hetereogeneities and reoptimized.
In general, the plan with heterogeneity:
a) requires smaller wedge angle
b)results in greater max tissue dose
c) results in higher skin dose

A

a
increased transmission through lung generally requires a smaller wedge for homogeneity

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16
Q

gap widh for 2 direct spine fields matched at 6 cm, 25 and 28 cm long
100 cm SAD

A

1.6 cm

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17
Q

100 cm sad
colli rotation required to align 25x25 cranial fields with a direct spinal field of height 36 cm

A

arc tan (18/100)

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18
Q

dose to pacemaker should be kept beloe 2 Gy. For 6 MV lung of 40 Gy, fields should be no closer than x cm to the pacemaker?

A

b - 2 cm
(used 3%/mm rule in lung)

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19
Q

pregnant woman is treated with 6 MV fields
total dose of 40 Gy
fetus is 15 cm from field edge. What will maximum dose to fetus be?

A

0.6 - 2% per AAPM TG 50

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20
Q

rule of thumb for mm of lead required per MeV for a cutour

A

-0.5 mm

(MeV/2) mm

21
Q

where is increased scatter from lead shielding in electron treatments?

A

increased dose at front, decreased dose at back
i.e. scatter from front surface

22
Q

when CT scans are used in treatment plans with heterogeneity corrections, QA should be done regularly to ensure constancy of all of the following except:
a. laser alignment’b. CT number vs electron density
c. absence of distortion
d. dose

A

answer was d since dose wouldn’t affect the TP

23
Q

100 slice CT SIm requires how much memory?

A

50 MB
512 X 512 X 2 bytes X 100 slices

24
Q

DICOM RT transfer protocol includes what?

A

CT image set with beam info and dose distribution

25
Q

orthogonal lateral films are taken. What would NOT improve resolution?
a. reduce collimator size
b. using higher grid ratio
c. increase mAs
d. take orthogonals at 45 and 315 degrees instead

A

increasing mAs does NOT improve contrast

(remember only improves contrast to noise ratio)

26
Q

which of the following would not be a factor used in calculating room shielding for HDR?
a. source energy
b. closest disance of unit to shielded wall
c. wall material
d. average source activity between installation and replacement
e. max workload

A

d. the max activity is used, not the average

27
Q

main advantage of EPID over conventional radiographic film:
a. improved resolution
b. improved SNR
c. less dose required
d. images can be digitally enhanced
e. all of the above

A

d

28
Q

when expanding a XX to create a YY, expansion into bone will typically be excluded.

A

GTV, CTV

Bone tends to limit spread of disease

PTV is for setup error, so is expanded into bone

29
Q

typical residual positioning error after IG setup

A

1-5 mm

don’t like this question as it depends on treatment setup

30
Q

advantages of CBCT vs dual ortho kV fluoro, all of the following are true except:
a. CBCT can’t be used in real time whereas fluoro can
b. CBCT delivers higher patient dose
c. CBCT can image soft-tissue differences whereas ortho fluoro cannot
d. CBCT has better spatial resolution

A

d is not true

31
Q

tomo includes which modalities?

A

MV CT
MV linac

32
Q

50% of points fail dose verification. Possible reasons could be the following except:
a. in TPS, converting from ideal fluence to deliverable plan resulted in poor plan
b. measured dept is different
c. measured SAD is different
d. Wrong field is chosen

A

a
because deliverable plan is what would be compared to measured

33
Q

which of the following regarding TBI is false?
a. -can use 6, 10, or 15 MeV photons
b. in certain orientations, tissue compensators are not needed
c. AP/PA or later POPs can be used
d. dose to lungs must be limited

A

b

34
Q

dose per minute for air kerma strength of HDR 192 source of 40,000 cGy cm2/h

A

divide by 60
cGy cm2/h is same as uGy m2/h

35
Q

exposure rate is 200 mR/h- max time someone can spend there

A

1 mSv/wk
use 0.876 cGy/R for conversion
1 Gy= 1 Sv

36
Q

for same initial dose rate, required activity of I-125 vs Ir 192

A

I 125 is higher because it has lower exposure rate constant

37
Q

wrt preferentially implanting seeds towards the periphery of the prostate vs uniform distribution of seeds within prostate, which of following statements is false?
a. dose to urethra will be lower
b. dose to rectum will be lower
c. dose to entire prostate will be more uniform
d. more easily achieved with LDR than HDR

A

b is false, it slightly increases rectal dose

dose is closer to see

38
Q

ideal tandem and ovoids, typualy dose rate at pt A

A

55 cGy/h

typical loading is 15-10-10 mg Ra in tandem
15 mG Ra eq in each ovoid

39
Q

HDR yields more toxicity to rectum compared to LDR. How is this reduced in HDR?
a. reduce dwell time in colpostats
b. reduce fractions
c. reduce dwell times in tandem closest to rectum
d. using rectal retractor or packing

A

d

40
Q

plane of uniform activity Ir-192 seeds is proposed. What system can be used to calculate required activity to meet a dose objective?
a. Peterson Parker
b. Quimby
c. commercial system
d. all of above
e. B and C

A

e
Peterson-Parker cannot be used for equal activity sources

41
Q

QA tests that should be performed before Mammosite treatment include verification of the constancy of all of the following except:
a. balloon dimensions
b. product of source activity and total dwell times
c. accuracy of source position
d, min distance from balloon to skin

A

d
this is checked during planning at begining of tx

doctor may choose not to treat if distance < 7 mm

42
Q

how is 18 F created

A

cyclotron

43
Q

how is Cs 137 created

A

by-product of fission

44
Q

how is Ir 192 created

A

bombard 191Ir with neutrons in a reactor

45
Q

lateral penumbra of proton beam vs photon beam

A

proton is superior at shallow depths, but comparable to or wider at large depths

46
Q

can there be neutron contamination in proton beams?

A

yes in passively scattered proton beam
-produced by scatter in collimators and energy degraders. This is reduced in spot-scanned photon beam

47
Q

how to calculate biological half life so that correct I131 dose can be administered?

A

give tracer dose prior to treatment and perform whole body assay the following day and a few days later

48
Q

what is used to heat tumour wit hyperthermia treatment

A

microwave radiation

49
Q

comparing prostate treatment using 5-field 15 MV IMRT photon treatment plan with proton plan using POPs, the later proton plan has:
z. lower integral body dose
b. better conformity to PTV
c. lower rectal dose
d. lower bladder dose
e. all of aboce

A

apparently a is only correct answer … I guess 5 field would avoid rectum and bladder as well…

RAPHEX (13 decks)

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