1098 / 1544
Breast IMRT
P. Jain et al. / Radiotherapy and Oncology 90 (2009) 93–98
r each
ot vol-
5% and
of dai-
nt sys-
n and
tic and
f indi-
d devi-
ted by
he vol-
on was
or and
ily EPI
Fig. 2
).
and in-
neated
ations
entage
volume increases (>15%) were observed in patients 2 and 4; the
largest percentage reduction (>15%) was observed in patient 9.
Daily PTV contours overlaid onto the planning CT are illustrated
for an example patient (
Fig. 4
).
Variation in patient positioning
No patients exceeded conventional verification tolerance limits.
The mean systematic and random components of setup error
determined for each patient using CBCT during the treatment
course are given in
Table 1
. Values greater than 5 mm are shown
in bold. All patients demonstrated a mean systematic error
>5 mm in at least one axis, mainly in the lateral (
X
) and longitudi-
nal (
Z
) axes. The population lateral systematic error was also
>5 mm, where shifts tended towards the left. All longitudinal shifts
were in the inferior direction. Mean individual and population ran-
dom errors were all
6
5 mm.
Table 2
shows the frequency and size of rotations recorded for
all patients. Rotations >2
!
were most frequent around the lateral
(
X
) axis, and all occurred in the positive (backwards) direction.
Y
Pt 1
Pt 2
Pt 3
Pt 4
Pt 5
Pt 6
Pt 7
Pt 8
Pt 9
Pt 10
Fig. 4.
Example RT planning image with original (pale blue) and superimposed
daily PTV contours.
iotherapy and Oncology 90 (2009) 93–98
95
Discussion
This study is the first to use daily on-treatment CBCT to assess
3D inter-fraction patient/organ motion throughout a course of
breast RT using IMRT, and to assess the consequences upon both
IMRT and standard RT dose homogeneity.
Breast depth and daily PTV varied from planning and fluctuated
throughout the treatment course for all patients
[12,13,23]
. It is
likely that the breast depth variations were due to short-term oe-
dema and vascular effects as a result of prior treatments, showing
that independent organ motion remains an important consider-
ation for improved verification methods. Unlike a previous study
[23]
, we found larger PTV changes (>15%) in some patients, and
no apparent pattern or regression trend (
P
= 0.366), indicating ran-
dom organ/patient motion over the RT course.
Despite meeting conventional setup verification tolerances, a
mean systematic shift >5 mm was measured using CBCT in at least
one axis in all women. It is possible that variations may be exagger-
ated, as patientswere required to lie in treatment position for longer,
and the required couchmovesmay have introduced some errors. Im-
age registration for patients with limited data CT scans was also
Table 2
Total rotational setup errors.
Rotations Lateral (
X
) axis (%) Vertical (
Y
) axis (%) Longitudinal (
Z
) axis (%)
0
6
2
!
70.8
84.9
98.1
2
!
4
!
22.6
12.3
1.9
>4
!
6.6
2.8
–
Table 3
Impact of daily PTV variations upon IMRT and conventional RT plans.
Isodose
level
IMRT plan
Standard tangential RT plan
Mean planned
volume (% PTV)
Mean delivered
volume (% PTV)
Mean planned
volume (% PTV)
Mean delivered
volume (% PTV)
>107%
0.1
0.3 ± 0.6
4.0
4.4 ± 1.9
>105%
0.5
1.8 ± 2.0
15.7
15.6 ± 3.7
>95% <105% 96.7
89.5 ± 5.1
82.5
79.3 ± 5.1
<95%
2.7
8.6 ± 4.0
1.8
5.1 ± 2.6
<90%
0.3
2.7 ± 2.9
0.2
1.9 ± 2.0
Table 1
Patient translational setup errors.
Patient
L/R cancer
Individual systematic error (cm)
Individual random error (cm)
X
= lateral
Y
= vertical
Z
= longitudinal
X
= lateral
Y
= vertical
Z
= longitudinal
1
L
0.58
!
0.23
0.50
0.29
0.30
0.27
2
L
!
0.02
!
0.11
0.77
0.36
0.34
0.37
3
R
0.10
!
0.34
0.83
0.43
0.37
0.39
4
L
!
0.68
!
0.07
0.26
0.39
0.38
0.19
5
L
0.12
!
0.02
0.79
0.21
0.20
0.38
6
R
0.53
!
0.33
0.41
0.28
0.46
0.37
7
R
1.24
0.30
0.21
0.39
0.40
0.30
8
L
0.71
!
0.05
0.30
0.33
0.25
0.17
9
R
0.87
0.20
0.57
0.44
0.34
0.24
10
L
!
0.20
!
0.65
0.61
0.50
0.28
0.28
Population error
0.57
0.28
0.23
0.39
0.35
0.32
96
Cone-beam imaging during breast IMRT
Fig. 5.
Spatial location of low-dose PTV regions at planning (a) and throughout subsequent treatment days (b–i) for P7 (worst-case).
Fig. 6.
Spatial location of high-dose PTV regions at planning (a), and throughout subsequent treatment days (b–i) for P3 (worst-case). The grey dot represents the PTV
isocentre.
Fig. 5.
Spatial location of low-dose PTV regions at planning (a) and throughout subsequent treatment days (b–i) for P7 (worst-c
P. Jain et al./Radiotherapy and Oncology 90 (2009) 93–98
PTV position
High dose
Low Dose