Tx planning info Flashcards
1
Q
incr fs = ? Sc & Sp
A
incr
2
Q
fs output based on
A
open fld equiv square
3
Q
Sc (CSF)/Sp (PSF) involves
A
blocking
4
Q
gap calc e- can abut separated only by width of
A
line
5
Q
fld size correction factor accounts for difference in ? with diff cone sizes & field sizes
A
output or dose rate
6
Q
incr E= ? geom penumbra
A
decr
7
Q
TAR only for what type of tx
A
SAD or iso for 4MV or Co-60
8
Q
TMR only for
A
SAD & isocentric for 6MV & up
9
Q
isodose curves shows what variaion
A
2D
10
Q
more depth= ? uniform & symmetrical
A
more-b/c incr scatter
11
Q
smaller beam=? flatness
A
poor
12
Q
larger fs= ? dmax
A
smaller
13
Q
hot spot is considered ?
A
@ least 2cm^2 (khan)
14
Q
dose @ any depth greatest @
A
CAX
15
Q
isodose shift measures ?
A
air gap or extra tissue
16
Q
wedge pair is 2 fields separated by less than? deg
A
180deg
17
Q
4 fld pelvis has ? target dose
A
higher
18
Q
4 fld diamond lowers dose where on pt
A
@ side of pt
19
Q
arc therapy is how much of a rotation
A
less than full rotation
20
Q
adding wedge reduces ?
A
hot spot
21
Q
wedges do not alter CAX of what E
A
Co-60 or 6x
22
Q
tissue inhomogeneity is inversely dependent on
A
photon E
23
Q
equal distribution is
A
unequal weighting of beams to get even distrib of dose/hotspots
24
Q
120% < D90 < 130% if dose is 160Gy means?
A
90% of ptv should receive b/n 192-208 Gy
25
weighting is used for asymmetric
volume
26
normalization relates a series of #s to
specific value
27
non-coplanar is used to produce ? distribution
more uniform distrib & avoid healthy tissue
28
conformal therapy is the usage of ? fields
MORE THAN 4 FIELDS w/a lot of blocking
29
cumulative DVH is the plot of volume of a structure receiving ?
certain dose or higher
30
differential DVH is a plot of volume receiving a dose within
a specific dose interval as a fxn of dose
31
obstacle in achieving optimal dose distrib is adequate knowledge of
tumor extent
32
optimization requires
fld apertures, beam weights, beam directions, modifiers, # flds
33
registration is correlating different image sets to
identify corresponding structure region
34
beam aperture is beam directions that create greater
separation b/n targets & critical structures
35
correction-based algorithm is limited for
3D heterogeneity correction in lungs & tissue interfaces
36
model based algorithm computes
dose distribution w/a PHYSICAL MODEL
37
convolution superposition is how accurate
most accurate model based algorithm
38
Clarkson method accounts for ? contribution determined by?
-scatter contribution, by avg SAR corresponding to each radius
39
ICRU stands for
-int'l commission of Rad Units & Meas
40
tx of superficial tumor with extended depth of 7 cm is
wedge pair technique
41
with adjacent flds for deep tumors need ? on skin
-separation; to enable junction or overlay @ depth
42
adjacent flds for superficial tumors can be ? on skin
abutted
43
primary reason to tattoo pts
to locate previous tx flds
44
advantage of universal wedge
beam widths
45
wedge pair assoc w/hot spot with larger ?
field size
46
ssd advantage over sad enables
fixed gantry location on the # of fields
47
pt with kyphosis beam is directed toward
head
48
upper extremity tx POP- arms are ? to axis of gantry
parallel to axis of gantry or rt angle to beam
49
hot/cold spots common with what technique
wedge pair
50
max & min tumor dose to surrounding tissue increase #
portals
51
to deliver highest dose to tumor & minimal to surrounding tissue, have Dmax dose centered over
tumor volume
52
isodose curves represent ? variation of absorbed dose
volumetric or planar variation; @ diff levels
53
increasing geometric field size makes dose build up
higher
54
first hvl of a heterogeneous x-ray beam is usually less than
2nd (thinner)
55
divergent blocks ? potential of partial transmission vs non-divergent block
decreases
56
cerrobend blocks are typically how thick
7 cm
57
field size ? if dose rate increases due to ?
increases; scatter almost entirely dependent on field size
58
a 10x10 field around a calc point will produce ? scatter than a 2x50 field
more
59
absorbed dose rate decr w/incr ?
distance
60
interactions more concentrated when distance is ?
increased
61
the size of the inhomogeneity will affect ?
dose
62
wedge angle is the angle through which an isodose curve is
tilted @ cax @ specific depth
63
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
dynamic wedge
64
correcting isocharts for irreg surfaces with photons is
2/3 of air gap
65
-depth @ which max dose or equivalent occurs is ? as fs is incr
reduced
66
single fld tx photons have a dose range w/i target of +/-?
5%
67
wedge flds are used in tx of what depth tumors
small shallow tumors
68
in an indep jaw, higher/lower dose is delivered where jaw was first set
higher
69
when ssd becomes ? or depth where beam sides converge increase, size of gap will be ?
shorter, larger
| -bentel fig 6.56; 6.46 pf 143/pg 153
70
proper gap shift is achieved by ? size of 1 field & ? size of adjacent field
incr, reducing
71
decr E = ? geom penumbra
incr
72
Sc is based on open
equivalent square
73
Sp is ? collimator setting
effective
74
Sp is based on blocked
equivalent square
75
PDD decr with ? depth
incr- b/c more attenuation
76
PDD comprises ? components
attenuation & inverse square
77
PDD falls less rapidly with ? E
high
78
TAR is ? at Dmax
backscatter
79
TAR is used for what kind of fields
-stationary isoctr & irreg flds- calc dose in block fld by breaking down into prim & scatter components
80
in TAR, calc dose in blocked fields by breaking down into components
primary & scatter components
81
TAR at Dmax is
1 or higher
82
TMR at Dmax?
always 1 @ dmax for any photon E but never >1
83
isodose curves are lines of
absorbed dose
84
isodose curves for high E appear
flatter & sharper
85
isodose curves display distribution in phantom by
joining points of equal absorbed dose
86
Clarkson Method is devised to calculate ? segments
separately calc scatter dose by dividing blocked field into 24 segments & finding SAR
87
Clarkson Method compares SAR to ? fields
circular
88
Clarkson Method corrects for
pt contour & blocks
89
rotational factors are used to find average ? for rotation fields
TAR
90
rotational factors use contour divided into ? segments
16-24 segments
91
isodose shift shifts curve ?
2/3 or 1/2 depending on beam E & machine
92
if air gap, isodose shift shifts lines ? in tissue
deeper
93
isodose shift factor ? as beam E incr
decr; b/c ISL & tissue attenuation
94
isodose shift direction of shift ? from tissue deficit
away
95
isodose shift direction of shift ? from tissue surplus
toward
96
parallel opposed fields shape
hour glass shape
97
wedge pair commonly used for
brain tumors, sinus tumors
98
wedge pair greatest depth is ? cm
9-10cm
99
wedge pair acceptable hot spot ?
10%
100
wedge pair disadvantage
hot/cold spots common
101
4 field pelvis reduces ? dose
entrance
102
arc therapy iso is placed
distal to tumor (past pointing-don't do anymore)
103
wedges incr ? of xray beams
TAR
104
wedges can alter ? especially at large depths for high E photons
depth dose distribution
105
tissue inhomogeneity is directly dependent on ? of inhomogeneity
dimensions
106
tissue inhomogeneity is dependent on ? of inhomogeneity
depth
107
shrinking fields is used because dose must be ? to sensitive norm structures
decreased
108
weighting is used if the volume is not ?
midplane
109
weighting is used to remove unwanted
hotspots
110
normalization relates to a ?
standard
111
normalization uses ? approaches
4
112
an obstacle in achieving optimal dose distrib is pt ?
motion & organ motion & pt/organ displacement
113
an obstacle in achieving optimal dose distrib is adequate knowledge of PTV within ? isodose lines to Rx dose
95-105%
114
an obstacle in achieving optimal dose distrib is ? response of ?
biological response of tumors & norm tissue
115
beam aperture requires a ? cm margin b/n PTV & field edge because?
2 cm margin to assume better than 95% isodose
116
correction based algorithm consists of ? correction for contour irregularities, scatter corrections
attenuation
117
Clarkson Method corrects ? component
scatter; for pt contour & blocks
118
ICRU recommends regarding ?
-recommendations regarding dose uniformity, prescribing, recording, reporting photon therapy
119
IM is added to ? for what?
CTV for physiologic movements & variation in size, shape, & position of CTV
120
SM is added to account for
uncertainties in pt positioning & alignment of therapeutic beams
121
SM is added to what volume and not part of what volume?
added to IM or ITV & NOT part of CTV
122
neg blocks commonly used for what tx
h&n
123
pos blocks commonly used for what tx
lung
124
wedge pair assoc w/hot spot with larger
wedge angle
125
kyphosis pt- gantry & table kicked
90 deg rotation of couch & gantry perpendicular to torso
126
max & min tumor dose to surrounding tissue limit
field size
127
divergence reduces beam ?
intensity
128
does transmission reduce beam intensity?
no
129
divergent blocks ? penumbra vs non-divergent blocks
decrease
130
cerrobend blocks have ~ ? HVL
5
131
dose rate ? more rapidly in smaller fields
incr
132
as field size becomes ? dose rate stabilizes
larger
133
as field size ? absorbed dose is greater b/c of ? scatter
increases, absorbed dose is greater b/c of incr scatter
134
the density of the inhomogeneity will affect
dose
135
the E of the beam will affect ? of the inhomogeneity
dose
136
wedge angle degree of tilt changes with
depth
- tilt decr @ greater depth b/c of incr scatter
- refers to tilt of iso curve- NOT angle of actual wedge
137
wedge angle degree referes to tilt of ? not actual wedge angle
iso curve
138
in correcting isodose charts for irregular surface with low E
shift increases
139
in correcting isodose charts for irregular surface with high E
shift decreases
140
as dmax shifts ? to surface-dose on surface also incr
closer
141
obl incident beams also ? skin sparing
reduce
142
shift in dmax toward surface also caused by ? arising in coll & devices
secondary e-
143
dmax shifted toward ? when beam intercepts tx couch, immob device, clothing, etc
surface
144
unlike photons, actual dose for e- on skin ? w/higher E beams
increases
145
lower E beams in e-, dose falls off ? w/depth after it has reached 100%
rapidly
146
higher E beams in e- peak is ? sharp & dose remains close to 100%
less
147
in POP, when thickness of tissue is ?, ratio b/n mid-depth & dmax remain acceptable
small
148
in POP, as thickness becomes ? or beam E decreases, ratio increases
larger
149
in POP, when thickness is ? & extends beyond linear portion of %DD curve, dose near entrance/exit is ? than @ mid-depth
larger, higher
150
in POP, highest intensity line
pinches in
151
wedge angle needed depends on the ?
hinge angle
152
dose gradient ? as coll moves across the fld
decreases
153
in rotational therapy, most situations using ? E results in sup dose distrib
high
154
in rotational therapy, the rate @ which dose ? @ the POI moves toward the periphery depends on fld width & beam E
decr
155
in rotational therapy wide fld, fall off in periphery is less/more dramatic than w/smaller fld
less
156
in arc tx, when sector skipped, ? dose area is shifted away from skipped sector
high
157
in arc tx, it is necessary to ? in order to bring the high dose region back to target
past point
158
in arc tx, when 2 asym sectors are skipped, iso must be shifted ? larger sector
toward
159
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
smaller
160
in adjacent fields, if abutting @ surface, there is ? @ depth
overlap
161
in adjacent fields, if there is a gap b/n flds, there is a (hot/cold) area in shallow region
cold
162
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
less
163
in adjacent fields, the gap moved (dose?) to prevent overlap in same tissue
every 10 Gy
164
in adjacent fields, it is preferable to make ? in location where no tumor
separation
165
in adjacent fields, the field margin b/n ?
vertebral bodies
166
single fld tx photons have a max dose of < ?%
110
167
Absorbed dose depends on
- E of radiation
| - material of mass
