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RAPHEX > RAPHEX IV > Flashcards

RAPHEX IV Flashcards

1
Q

what is responsible for nuc med imaging with 99mTc?

A

gamma rays

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2
Q

which of the following is true? I-131 and I-125 have…
a. have different chemical properties
b. have different Z values
c. have the same number of neutrons
d. none of the above

A

none of the above
chemically, all isotopes are identical. Isotopes have the same Z but different number of neutrons (and hence mass number)

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3
Q

there are 2 of these in a tritium nucleus

A

neutrons
H-3 has one proton and 2 neutrons

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4
Q

which of the following does NOT occur when a linac is changed from xray mode to electron mode?
a. target is removed
b. scattering foil placed in beam
c. monitor chamber is removed
d. electron applicator attached
e. beam current decreases

A

c monitor chamber remains

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5
Q

what is predominant reaction by which fast neutrons dissipate energy in tissue?

A

elastic collisions with H nuclei in tissue

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6
Q

Compton photon is backscattered at min energy, what angle is electron emitted relative to direction of initial photon?

A

photon at 180 degrees, electron at 0 degrees

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7
Q

dmax is approx equal to…

A

-d where kerma and dose are equal
-max range of secondary electrons
-depth at which CPE occurs

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8
Q

to convert R to mGy, factor for diagnostic xrays and muscle tissues is closest to?
-0.1
-5
-9
-2
-90

A

0.876 cGy/R = 8.76 mGy/R therefore 9

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9
Q

per TG51, do electron beams have to be calibrated with chambers having a electron calibration factor from NRC?

A

no, can be cross-calibrated with a NRC calibrated chamber

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10
Q

dose beyond dense bone in 6 MV beam, compared to that calculated without heterogeneity correction

A

6 % less
ie. 2%/cm
also bone density is 1.6X water; therefore 3 c bone is additional 1.8 cm of tissue
attenuation of 6 MV beam is 3.5%/cm

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11
Q

dmax of 6 MeV electrons

A

1.2 cm

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12
Q

patient with 10 MV POP fields, 20x20cm2, 100 cm SAD. 4500 cGy in 25 fractions. AP thickness is 26 cm. What is total dose per fx at dmax?
a. 162
b. 175
c. 180
d. 194
e. 216

A

total dose at dmax must be greater than midplane dose

For 10 MV xrays d is only reasonable answer./ (separation of 34 cm would be needed for 20% higher)

PDD for 10 MV at 10 cm depth is around 73%; 180/2 / 0.73 = 123 cGy (for one beam)

PDD for 20 cm is 0.46, 123 * 0.46 = 56 cGy

123 + 56 cGy = 179 cGy
d is reasonable

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13
Q

changing POPs from 100 cm SAD to 100 cm SSD while treating to the same Rx dose at patient midline would cause which of the following changes in MU and total dose at dmax?

A

As Rx moves farther away, MU must increase. Increasing SSD increases the PDD; therefore total dose at dmax is slightly smaller

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14
Q

all of the following statements are true for breast tangents with wedges expect:
a. wedges can reduce hot spot at apex
b.contralateral intact breast will receive less dose compared with open-field treatment because the wedge will block scatter dose from the gantry head
c.dynamic wedges do not harden the beam
d. dose scattered to the contra breast is less for dynamic wedges than for conventional wedges

A

b
although the wedge blocks some scatter from the tx head, the wedge produces low energy scatter so the contra breast recieves more dose

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15
Q

all of the following are true regarding dynamic wedges except
a. the wedge effect is created by closing one collimator jaw during irradiation
b.the field length in the non-wedged direction cab ne equal to the max collimator setting
c.the depth dose on the beam axis is the same as that of an open beam
d.for a wedge in the y direction, one of the collimators cannot be set to 0

A

d

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16
Q

a 10x10 photon beam is used to deliver 100 cGy at 100 cm depth. If a 2x2 cm central block with 5% narrow beam transmission is used to protect a crticial organ, what happens to the dose on the central axis at the same depth?

A

it is greater than 5 cGy due to scatter from surrounding tissue

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17
Q

electron field size required to treat a volume with a 5 cm width at treatment depth

A

7 cm- need 1 cm on either side

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18
Q

boost with 16 MeV electrons with 3 cm diameter cut-out in 6x6cm cone. Field must be treated at 115 cm SSD to avoid shoulder/ All the following are true except:
1. electron output (cGy/MU) is reduced compared to 6x6cm cone
2.penumbra width will increase, compared to that at 100 cm SSD
3.depth of the 90% isodose will be less than that of open 6x6 cm cone
4.output at 115 cm SSD will be (100/115)^2 times that at 100 cm SSD

A

d
for electrons, output can be corrected by IS law only when virtual SSD is used. Have to measure output for the actual cut-out and SSD to be used

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19
Q

if air gap between electron cutout and skin increases from 5 cm to 10 cm, the max dose in tissue for the same MU decreases by about..

A

10%

SMALL air gap canges on electron beams need correction proportional to IS law, which is 2%/cm

20
Q

what does DICOM do?

A

defines file formats and network communication

21
Q

average surface anterior air kerma rate at the symphysis pubis from patients receiving I-125 seed implantation in the prostate is about:

A

25 uGy/h

22
Q

TMR depends on…

A

energy, depth, FS
NOT SAD because both measurements are at same SAD

23
Q

a patient treated with 6 MV breast tangents requests a lead apron to shield her ovaries. All of the following are true except:
a. the ovaries are far enough away that they would receive no measurable dose
b.6 MV head leakage has HVL of 12 mm of Pb
c.a typical Pb apron contains about 0.5 mm of Pb, which would hae negligible shielding effect
d. the lead apron is ineffective against internal scatter

A

a
ovaries would receive about 0.5% of dose, or 25 cGy

to shield against head leakage and collimator scatter would require a substantial amount of Pb

24
Q

process that dominates for 120-140 kV photons

A

Compton, but enough PE effect to get contrast

25
Q

PET/CT fusion can have which problems:
a.high doses of FDG can cause artifacts on CT image
b. PET resolution is much better than that of CT
c. Long PET scan times can increase apparent tumor size due to respiration
d,hypoxia cannot be detected with PET

A

c
could use gating to improve this
but then also use same gating for tx

26
Q

US can be used to localize all of the following except:
a. site of surgical resection of brain lesion
b. prostate seed implants
c. prostate EBRT
d. breast lumpectomy site

A

a
US cannot penetrate dense bone

27
Q

where does conversion of xrays into electrons occurs in EPID?

A

metal plate in front of EPID

phosphor screen converts electrons into visible light
diode converts visible lights into electron-ion pairs

28
Q

which linac portal imaging system provides best image resolution?
a. liquid ion chamber array
b. fluorescent screen with CCD camera
c. amorphous silicon array
d. radiographic portal film

A

d
radiographic film is better resolution than any digital system

29
Q

to obtain a DVH, all of the following are requires except
a. 3D patient data set
b. 3D definition of PTV and OARs
c. 3D dose computation of all points in CT data set
d. 3D planning system

A

c
only pts in PTV and OARs need to be computed

30
Q

can you use kV orthos of bony anatomy to match prostate for tx setup?

A

no
bony anatomy is not a surrogate because it doesn’t follow motion of prostate

31
Q

what does tomo use for setup verification?

A

MV FBCT

32
Q

all of the following are true of IMRT except?
a. IMRT dose distributions are always more inhomogeneous than conventional 3D plans
b. in prostate, IMRT can reduce rectal toxicity
c.a 3D data set is required for IMRT planning
d. immobilization is more important because of tighter margins

A

a

33
Q

potential advantages of IMRT over 3DCRT include all of the following except:
a. dose conformity for irregularly shaped volumes
b. possibility of dose escalation
c. reduced OAR morbidity at conventional tumor doses
d. ability to treat a volume with a concave surface, conformally
e. significantly lower hot spots in the PTV

A

e

hot spots could be higher but not always case

I don’t like this question

34
Q

do you use lung blocks in TSEI?

A

no

35
Q

can cyberknife allow gating?

A

yes

36
Q

can cyberknife be used for SRS?

A

yes

37
Q

all of the following are good reasons for moving from low dose rate to high dose rate brachy in tx of cervical cancer except:
a. higher dose rate is radiobiolgically advantageous
b. geometry: shorter irradiation time assures packing will not move during imolant
c. shielding: irradiation of staff members doesnt exist
d. less chance of deep vein thrombosis
e. possibility of only one OR visit

A

don’t need shielding for staff as HDR is low exposure
answer is a; higher dose rate is NOT radiobiologically advantageous

38
Q

appropriate brachy applicator for stage IIIB cervical cancer

A

MUPIT

39
Q

I-125 seeds are used in brachy for what kind of radiation?

A

x0ray and gamma ray

I-125 decays by electron capture to 125 Te. It decays to ground state by emitting 35.5 keV gammas. Internal conversion gives rise to charcateristic xrays of 27-35 keV

40
Q

can Ir-192 be used as seeds for temporary implants

A

apparently yes

41
Q

which isotope is used for temporary eye implant?

A

I-125

42
Q

what stats govern radioactive decay?

A

poisson

43
Q

problems with hyperthermia

A

-difficulty achieving uniform heating
-difficulty measurng temperatures accurately
-doing treatment planning before tx

-having adequate QA is not a problem

44
Q

what limits ability to uniformly heat tumors in hyperthermia?

A

-ability to deposit energy uniformly
-blood flow in tumors
-different theraml properties of tissue

45
Q

a 2 cm air gap ion the path of which beam will generate the largest inhomogeneity correction?
a.15 MV photons
b. 6 MV photons
c. 170 MeV protons
d. 14 MeV neutrons

A

c
air is 800 X less dense than tissue, so 2 cm air gap will shift the bragg peak of a proton beam 2cm into the underlying tissues. Corrections for 2 cm air are only a few percent for photon and neutron beams

46
Q

which is true for proton radiotherapy compared to 15 MV xrays?
a. skin dose is usually lower for protons
b. lateral dose penumbra at deoths greater than 15 cm is usually better for protons
c. OER is significantly lower for protons
d. Integral whole body dose is lower for protons

A

d

RAPHEX (13 decks)

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