ESTRO 36 Abstract Book

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S90 ESTRO 36 2017
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Material and Methods
Anthropomorphic plastic phantoms were made with each
having a simulated tumor bed that can be visualized using
both ultrasound and CT. In the control, arm, the tumor is
identified using ultrasound and inserted under ultrasound
guidance.
A tissue-locking needle and US probe are equipped with a
real-time EM tracker. Under US guidance, the localization
needle is placed within the tumor bed, which provides a
rigid reference. The cavity is then contoured on US,
creating a model in a virtual view. An EM tracked needle
guide is pointed at the tumor bed and the catheter needle
is inserted through the guide into the tissue. Additional
parallel catheters are planned on the virtual view based
on the first insertion and implanted in the target. The
guidance software is built on the 3D Slicer
) and SlicerIGT ) open
source platforms.
In these experiments, a total of 10-15 catheters were
inserted in each of the six phantoms. The goal was to place
each catheter within the tumor bed. Three phantoms had
catheter needles inserted with ultrasound only, while the
other three had catheters inserted with combined EM
tracking and US guidance. All six insertions were
conducted by the same operator and the placement of the
catheters was determined with CT.
Results
Under US guidance only in the three phantoms, 17 out of
26 catheters passed through the tumor bed. The average
mean spacing was 0.86 cm +/- 0.33 cm. Under combined
EM tracking and US guidance, 35 out of 40 catheters
passed through the tumor bed. The average mean spacing
was 1.05 +/- 0.19 cm.
Conclusion
These phantom experiments verify that EM tracking can
be used to target catheter needles to the tumor bed.
Additional research is currently being performed to
translate this technique to patient trials.
OC-0179 Dosimetric impact of errors in HDR-iBT of the
breast using a catheter tracking method
M. Kellermeier1, B. Hofmann1, V. Strnad1, C. Bert1
1 Universitätsklinikum Erlangen- Friedrich-Alexander-
Universität Erlangen-Nürnberg, Department of Radiation
Oncology, Erlangen, Germany
Purpose or Objective
Electromagnetic tracking (EMT) was used to measure the
implant geometry in fractioned HDR interstitial
brachytherapy (iBT) of the breast. Based on the tracking
data the dosimetric impact of common clinical errors, e.g.
as reported in the United States by the Nuclear Regulatory
Commission, were assessed using treatment planning
quality criteria (QC).
Material and Methods
For tracking of implant catheters, 28 patients were
accrued within an institutional review board-approved
study. The geometry of interstitial single-leader catheters
(median: 18 pcs) was tracked on the HDR treatment table
directly after each of the treatment fraction (up to nine
during five days). Tracking has been performed by manual
insertion of a small EMT sensor into each of the catheters.
The breathing motion was compensated by computing the
center of mass from three additional EMT sensors on the
breast. Taking the tracking-based catheter data, different
errors (swaps and shifts of catheters, changing the
tracking direction of catheters, i.e. tip-end swap) were
simulated.
For dose calculation, the dwell positions (DPs) were
determined along the catheter traces and the dwell times
were taken from the approved treatment plan. Common
contour-independent QC like the dose non-uniformity
ratio (DNR) were analyzed. For investigation of contour-
dependent QC, like the coverage index (CI) of the PTV, the
corresponding EMT-derived DPs were registered to the CT-
derived DPs from treatment planning. In addition, the
maximal dose to the skin was determined. QC of EMT-
based dose distributions were normalized to the
corresponding values from treatment planning, so the
relative changes are reported.
Results
Without simulated errors, the maxim um dosimetric
deviations to the treatment plan were found on the 2nd
treatment day in median -6.2% for the DNR and -4.3% for
the CI of the PTV.
For error simulation, 15,107 pairwise swaps of catheters
were analyzed. The reconstructed dose distributions
resulted in DNR changes form -22.7% to 38.9% (mean:
0.6%, SD: 5.5%) and CI changes from -63.5% to 11.4%
(mean: -7.4%, SD: 7.8%).
For each shift of single catheters, 2,264 combinations of
dose distributions were calculated. Relative dosimetric
changes for DNR ranged from -4.1% to 3.5%, from -6.8% to
6.2% and from -8.8% to 8.1% for catheter shifts of 5, 10
and 15 mm, respectively at mean values between 0.0% and
-0.3%. The CI for the PTV showed a mean change of -0.3%,
-1.3% and -2.8%, respectively. Increased catheter shifts
correlated with a higher local dose at the skin (see
figures). In addition, each 3D dose distribution was
analyzed to identify individual local dose deviations.
Conclusion
Statistically, the maximum dose deviation was found on
the 2nd day, what might impact boost treatments with two
fractions only. Based on EMT-determined dose
calculations adaptive treatment protocols and tests for
possible treatment delivery errors should be
implemented. Further work is required for the registration
method.
OC-0180 Prospective study of APBI With Multicatheter
Brachytherapy in Local Relapses of Breast Cancer
E. Villafranca Iturre1, L. Rubi 2, M. Barrado1, A. Sola1, P.
Navarrete1, A. Manterola1, M. Dominguez1, G. Asin1, M.
Campo1, I. Visus1, G. Martinez1
1Hospital of Navarra, Radiation Oncology, Pamplona,
Spain
2Hospital Juan Ramon Jimenez, Radiation Oncology,
Huelva, Spain
Purpose or Objective