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Dosimetry > Tx planning info > Flashcards

Tx planning info Flashcards

1
Q

incr fs = ? Sc & Sp

A

incr

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2
Q

fs output based on

A

open fld equiv square

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3
Q

Sc (CSF)/Sp (PSF) involves

A

blocking

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4
Q

gap calc e- can abut separated only by width of

A

line

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5
Q

fld size correction factor accounts for difference in ? with diff cone sizes & field sizes

A

output or dose rate

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6
Q

incr E= ? geom penumbra

A

decr

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7
Q

TAR only for what type of tx

A

SAD or iso for 4MV or Co-60

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8
Q

TMR only for

A

SAD & isocentric for 6MV & up

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9
Q

isodose curves shows what variaion

A

2D

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10
Q

more depth= ? uniform & symmetrical

A

more-b/c incr scatter

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11
Q

smaller beam=? flatness

A

poor

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12
Q

larger fs= ? dmax

A

smaller

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13
Q

hot spot is considered ?

A

@ least 2cm^2 (khan)

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14
Q

dose @ any depth greatest @

A

CAX

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15
Q

isodose shift measures ?

A

air gap or extra tissue

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16
Q

wedge pair is 2 fields separated by less than? deg

A

180deg

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17
Q

4 fld pelvis has ? target dose

A

higher

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18
Q

4 fld diamond lowers dose where on pt

A

@ side of pt

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19
Q

arc therapy is how much of a rotation

A

less than full rotation

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20
Q

adding wedge reduces ?

A

hot spot

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21
Q

wedges do not alter CAX of what E

A

Co-60 or 6x

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22
Q

tissue inhomogeneity is inversely dependent on

A

photon E

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23
Q

equal distribution is

A

unequal weighting of beams to get even distrib of dose/hotspots

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24
Q

120% < D90 < 130% if dose is 160Gy means?

A

90% of ptv should receive b/n 192-208 Gy

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25
Q

weighting is used for asymmetric

A

volume

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26
Q

normalization relates a series of #s to

A

specific value

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27
Q

non-coplanar is used to produce ? distribution

A

more uniform distrib & avoid healthy tissue

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28
Q

conformal therapy is the usage of ? fields

A

MORE THAN 4 FIELDS w/a lot of blocking

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29
Q

cumulative DVH is the plot of volume of a structure receiving ?

A

certain dose or higher

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30
Q

differential DVH is a plot of volume receiving a dose within

A

a specific dose interval as a fxn of dose

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31
Q

obstacle in achieving optimal dose distrib is adequate knowledge of

A

tumor extent

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32
Q

optimization requires

A

fld apertures, beam weights, beam directions, modifiers, # flds

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33
Q

registration is correlating different image sets to

A

identify corresponding structure region

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34
Q

beam aperture is beam directions that create greater

A

separation b/n targets & critical structures

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35
Q

correction-based algorithm is limited for

A

3D heterogeneity correction in lungs & tissue interfaces

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36
Q

model based algorithm computes

A

dose distribution w/a PHYSICAL MODEL

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37
Q

convolution superposition is how accurate

A

most accurate model based algorithm

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38
Q

Clarkson method accounts for ? contribution determined by?

A

-scatter contribution, by avg SAR corresponding to each radius

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39
Q

ICRU stands for

A

-int’l commission of Rad Units & Meas

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40
Q

tx of superficial tumor with extended depth of 7 cm is

A

wedge pair technique

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41
Q

with adjacent flds for deep tumors need ? on skin

A

-separation; to enable junction or overlay @ depth

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42
Q

adjacent flds for superficial tumors can be ? on skin

A

abutted

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43
Q

primary reason to tattoo pts

A

to locate previous tx flds

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44
Q

advantage of universal wedge

A

beam widths

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45
Q

wedge pair assoc w/hot spot with larger ?

A

field size

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46
Q

ssd advantage over sad enables

A

fixed gantry location on the # of fields

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47
Q

pt with kyphosis beam is directed toward

A

head

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48
Q

upper extremity tx POP- arms are ? to axis of gantry

A

parallel to axis of gantry or rt angle to beam

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49
Q

hot/cold spots common with what technique

A

wedge pair

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50
Q

max & min tumor dose to surrounding tissue increase #

A

portals

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51
Q

to deliver highest dose to tumor & minimal to surrounding tissue, have Dmax dose centered over

A

tumor volume

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52
Q

isodose curves represent ? variation of absorbed dose

A

volumetric or planar variation; @ diff levels

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53
Q

increasing geometric field size makes dose build up

A

higher

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54
Q

first hvl of a heterogeneous x-ray beam is usually less than

A

2nd (thinner)

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55
Q

divergent blocks ? potential of partial transmission vs non-divergent block

A

decreases

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56
Q

cerrobend blocks are typically how thick

A

7 cm

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57
Q

field size ? if dose rate increases due to ?

A

increases; scatter almost entirely dependent on field size

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58
Q

a 10x10 field around a calc point will produce ? scatter than a 2x50 field

A

more

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59
Q

absorbed dose rate decr w/incr ?

A

distance

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60
Q

interactions more concentrated when distance is ?

A

increased

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61
Q

the size of the inhomogeneity will affect ?

A

dose

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62
Q

wedge angle is the angle through which an isodose curve is

A

tilted @ cax @ specific depth

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63
Q

the side of field where starting position of moving leaf is located will receive higher dose than side where final position is located is called

A

dynamic wedge

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64
Q

correcting isocharts for irreg surfaces with photons is

A

2/3 of air gap

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65
Q

-depth @ which max dose or equivalent occurs is ? as fs is incr

A

reduced

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66
Q

single fld tx photons have a dose range w/i target of +/-?

A

5%

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67
Q

wedge flds are used in tx of what depth tumors

A

small shallow tumors

68
Q

in an indep jaw, higher/lower dose is delivered where jaw was first set

A

higher

69
Q

when ssd becomes ? or depth where beam sides converge increase, size of gap will be ?

A

shorter, larger

-bentel fig 6.56; 6.46 pf 143/pg 153

70
Q

proper gap shift is achieved by ? size of 1 field & ? size of adjacent field

A

incr, reducing

71
Q

decr E = ? geom penumbra

A

incr

72
Q

Sc is based on open

A

equivalent square

73
Q

Sp is ? collimator setting

A

effective

74
Q

Sp is based on blocked

A

equivalent square

75
Q

PDD decr with ? depth

A

incr- b/c more attenuation

76
Q

PDD comprises ? components

A

attenuation & inverse square

77
Q

PDD falls less rapidly with ? E

A

high

78
Q

TAR is ? at Dmax

A

backscatter

79
Q

TAR is used for what kind of fields

A

-stationary isoctr & irreg flds- calc dose in block fld by breaking down into prim & scatter components

80
Q

in TAR, calc dose in blocked fields by breaking down into components

A

primary & scatter components

81
Q

TAR at Dmax is

A

1 or higher

82
Q

TMR at Dmax?

A

always 1 @ dmax for any photon E but never >1

83
Q

isodose curves are lines of

A

absorbed dose

84
Q

isodose curves for high E appear

A

flatter & sharper

85
Q

isodose curves display distribution in phantom by

A

joining points of equal absorbed dose

86
Q

Clarkson Method is devised to calculate ? segments

A

separately calc scatter dose by dividing blocked field into 24 segments & finding SAR

87
Q

Clarkson Method compares SAR to ? fields

A

circular

88
Q

Clarkson Method corrects for

A

pt contour & blocks

89
Q

rotational factors are used to find average ? for rotation fields

A

TAR

90
Q

rotational factors use contour divided into ? segments

A

16-24 segments

91
Q

isodose shift shifts curve ?

A

2/3 or 1/2 depending on beam E & machine

92
Q

if air gap, isodose shift shifts lines ? in tissue

A

deeper

93
Q

isodose shift factor ? as beam E incr

A

decr; b/c ISL & tissue attenuation

94
Q

isodose shift direction of shift ? from tissue deficit

A

away

95
Q

isodose shift direction of shift ? from tissue surplus

A

toward

96
Q

parallel opposed fields shape

A

hour glass shape

97
Q

wedge pair commonly used for

A

brain tumors, sinus tumors

98
Q

wedge pair greatest depth is ? cm

A

9-10cm

99
Q

wedge pair acceptable hot spot ?

A

10%

100
Q

wedge pair disadvantage

A

hot/cold spots common

101
Q

4 field pelvis reduces ? dose

A

entrance

102
Q

arc therapy iso is placed

A

distal to tumor (past pointing-don’t do anymore)

103
Q

wedges incr ? of xray beams

A

TAR

104
Q

wedges can alter ? especially at large depths for high E photons

A

depth dose distribution

105
Q

tissue inhomogeneity is directly dependent on ? of inhomogeneity

A

dimensions

106
Q

tissue inhomogeneity is dependent on ? of inhomogeneity

A

depth

107
Q

shrinking fields is used because dose must be ? to sensitive norm structures

A

decreased

108
Q

weighting is used if the volume is not ?

A

midplane

109
Q

weighting is used to remove unwanted

A

hotspots

110
Q

normalization relates to a ?

A

standard

111
Q

normalization uses ? approaches

A

4

112
Q

an obstacle in achieving optimal dose distrib is pt ?

A

motion & organ motion & pt/organ displacement

113
Q

an obstacle in achieving optimal dose distrib is adequate knowledge of PTV within ? isodose lines to Rx dose

A

95-105%

114
Q

an obstacle in achieving optimal dose distrib is ? response of ?

A

biological response of tumors & norm tissue

115
Q

beam aperture requires a ? cm margin b/n PTV & field edge because?

A

2 cm margin to assume better than 95% isodose

116
Q

correction based algorithm consists of ? correction for contour irregularities, scatter corrections

A

attenuation

117
Q

Clarkson Method corrects ? component

A

scatter; for pt contour & blocks

118
Q

ICRU recommends regarding ?

A

-recommendations regarding dose uniformity, prescribing, recording, reporting photon therapy

119
Q

IM is added to ? for what?

A

CTV for physiologic movements & variation in size, shape, & position of CTV

120
Q

SM is added to account for

A

uncertainties in pt positioning & alignment of therapeutic beams

121
Q

SM is added to what volume and not part of what volume?

A

added to IM or ITV & NOT part of CTV

122
Q

neg blocks commonly used for what tx

A

h&n

123
Q

pos blocks commonly used for what tx

A

lung

124
Q

wedge pair assoc w/hot spot with larger

A

wedge angle

125
Q

kyphosis pt- gantry & table kicked

A

90 deg rotation of couch & gantry perpendicular to torso

126
Q

max & min tumor dose to surrounding tissue limit

A

field size

127
Q

divergence reduces beam ?

A

intensity

128
Q

does transmission reduce beam intensity?

A

no

129
Q

divergent blocks ? penumbra vs non-divergent blocks

A

decrease

130
Q

cerrobend blocks have ~ ? HVL

A

5

131
Q

dose rate ? more rapidly in smaller fields

A

incr

132
Q

as field size becomes ? dose rate stabilizes

A

larger

133
Q

as field size ? absorbed dose is greater b/c of ? scatter

A

increases, absorbed dose is greater b/c of incr scatter

134
Q

the density of the inhomogeneity will affect

A

dose

135
Q

the E of the beam will affect ? of the inhomogeneity

A

dose

136
Q

wedge angle degree of tilt changes with

A

depth

  • tilt decr @ greater depth b/c of incr scatter
  • refers to tilt of iso curve- NOT angle of actual wedge
137
Q

wedge angle degree referes to tilt of ? not actual wedge angle

A

iso curve

138
Q

in correcting isodose charts for irregular surface with low E

A

shift increases

139
Q

in correcting isodose charts for irregular surface with high E

A

shift decreases

140
Q

as dmax shifts ? to surface-dose on surface also incr

A

closer

141
Q

obl incident beams also ? skin sparing

A

reduce

142
Q

shift in dmax toward surface also caused by ? arising in coll & devices

A

secondary e-

143
Q

dmax shifted toward ? when beam intercepts tx couch, immob device, clothing, etc

A

surface

144
Q

unlike photons, actual dose for e- on skin ? w/higher E beams

A

increases

145
Q

lower E beams in e-, dose falls off ? w/depth after it has reached 100%

A

rapidly

146
Q

higher E beams in e- peak is ? sharp & dose remains close to 100%

A

less

147
Q

in POP, when thickness of tissue is ?, ratio b/n mid-depth & dmax remain acceptable

A

small

148
Q

in POP, as thickness becomes ? or beam E decreases, ratio increases

A

larger

149
Q

in POP, when thickness is ? & extends beyond linear portion of %DD curve, dose near entrance/exit is ? than @ mid-depth

A

larger, higher

150
Q

in POP, highest intensity line

A

pinches in

151
Q

wedge angle needed depends on the ?

A

hinge angle

152
Q

dose gradient ? as coll moves across the fld

A

decreases

153
Q

in rotational therapy, most situations using ? E results in sup dose distrib

A

high

154
Q

in rotational therapy, the rate @ which dose ? @ the POI moves toward the periphery depends on fld width & beam E

A

decr

155
Q

in rotational therapy wide fld, fall off in periphery is less/more dramatic than w/smaller fld

A

less

156
Q

in arc tx, when sector skipped, ? dose area is shifted away from skipped sector

A

high

157
Q

in arc tx, it is necessary to ? in order to bring the high dose region back to target

A

past point

158
Q

in arc tx, when 2 asym sectors are skipped, iso must be shifted ? larger sector

A

toward

159
Q

in arc tx, when target off ctr, adv to tx only thru region when depth of iso is ? & to skip a sector where depth is larger

A

smaller

160
Q

in adjacent fields, if abutting @ surface, there is ? @ depth

A

overlap

161
Q

in adjacent fields, if there is a gap b/n flds, there is a (hot/cold) area in shallow region

A

cold

162
Q

in adjacent fields, a wider penumbra makes dose (less/more) sensitive to small errors in fld sep b/c dose fall off is more gradual

A

less

163
Q

in adjacent fields, the gap moved (dose?) to prevent overlap in same tissue

A

every 10 Gy

164
Q

in adjacent fields, it is preferable to make ? in location where no tumor

A

separation

165
Q

in adjacent fields, the field margin b/n ?

A

vertebral bodies

166
Q

single fld tx photons have a max dose of < ?%

A

110

167
Q

Absorbed dose depends on

A
  • E of radiation

- material of mass

Dosimetry (53 decks)

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