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ESTRO 36 2017
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[1] Rit S et al, Med Phys 2009;36:2283-96.
[2] Fassi A et al, Phys Med Biol 2015;60:1565-82.
Results
Tumor visibility on CBCT images was limited to a small
range of projection angles, corresponding to about 5
seconds of each CBCT scan. Table 1 reports the tracking
errors measured along the vertical image dimension, i.e.
the projection of the superior-inferior tumor motion, and
along the horizontal image dimension, combining antero-
posterior and medio-lateral tumor motion. The absolute
tracking error, averaged over all CBCT scans of all
patients, measured 1.0 ± 0.9 mm and 0.8 ± 0.7 mm for the
horizontal and vertical image dimensions, respectively.
The comparison of real and estimated tumor trajectories
along the vertical dimension is depicted in Figure 1. A
significant correlation (p-value < 0.005) was found
between real and estimated tumor motion, with
correlation coefficients higher than 0.75 and 0.69 for the
horizontal and vertical dimensions, respectively.
Conclusion
We developed and tested a novel approach for intra-
fraction lung tumors tracking, using CBCT-based motion
models driven by an external breathing surrogate obtained
from non-invasive optical surface imaging. Compared to
CT-based motion models, the proposed method does not
need to compensate for inter-fraction motion variations
that can occur between planning and treatment phases.
The validation of the proposed approach on a wider
patient population is currently ongoing.
EP-1630 The impact of DIBH on dose to the junction in
loco-regionally treated left-sided breast patients
M. Van Hinsberg
1
, I. De Bree
2
, E. Osté
2
, D. De Ronde
2
1
Zuidwest Radiotherapeutisch Instituut, Klinische Fysica,
Vlissingen, The Netherlands
2
Zuidwest Radiotherapeutisch Instituut, RTT, Vlissingen,
The Netherlands
Purpose or Objective
Irradiating loco-regional left sided breast cancer patients
using a field matching technique is common practice in
clinical routine. Possible under- and overdosages at the
junction are normally reduced by the natural breathing of
the patient. Adding a (deep inspiration) breathhold
strategy introduces extra risks of under- and overdosage
in this region.
A modified conventional treatment technique for the
irradiation of loco-regional left-sided breast patients
combined with a voluntary DIBH technique has been
introduced in our institute. The objective of this pilot is
to validate that this technique is safe, robust and well
tolerated by the patient.
Material and Methods
The standard conventional irradiation technique is
adapted to become less sensitive to different
intrafractional DIBH levels.
A less steep penumbra at the junction is obtained by
creating several subbeams with different MLC-positions. In
order to reduce the number of beams, a selection of these
beams are grouped to one beam using the Field in Field
(FiF) forward IMRT functionality of Varian Eclipse
TM
TPS.
This resulted in treatment plans with 6 to 9 beams.
The study consists of the following steps:
1 The field match is validated using film measurements in
a phantom.
2 Dose distributions and relative movements for 6 patients
were assessed in vivo. For this a strip of film (with 6 mm
buildup) was placed on the patient skin at the junction. In
addition markers were placed on the skin above, on and
below the junction, next to the film. Relative movements
of the markers in each DIBH were determined using MV-
images.
3 The relative movements of the marker measured in each
DIBH were used to position the beams in the corresponding
location in the TPS, resulting in a realistic dose
distribution for each fraction and for the total treatment.
4 The in-vivo film measurements were used as a validation
for the skin dose distribution calculated as explained in 3.
Results
The measured relative marker positions of all patients are
shown in fig.1.
Fig. 1 Marker positions relative to the fraction mean.
Distribution mean 0.4 mm; sd 2mm; range; -7 to 8 mm. A
negative sign means the patient has moved in caudal
direction.
Analysing the marker positions of each patient shows no
trend between the DIBH level of the first and last beam.
No hyperventilating nor exhaustion occurred, indicating
that DIBH with 6 to 9 beams is well tolerated.
Planned dose-values and actual, total dose values for the
CTV
are presented in table 1: