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was also used to assess the registration error of
CT
T
OTS
. To
prove the overall accuracy of this approach, another in-
house developed phantom was used, equipped with eleven
catheters and eight IR-markers. The feasibility of a daily
patient data acquisition was examined in an institutional
review board-approved study by using the afterloader
prototype and the OTS in addition to regular iBT
treatments.
Results
Based on different poses of the calibration tool, the root
mean square errors for
OTS
T
EMT
and
CT
T
OTS
were 0.56 mm
and 0.49 mm, respectively. The overall accuracy of
CT
T
EMT
resulted in 0.74 mm. The determined transformations
were applied to the phantom measurements and showed
a mean deviation to the CT data of 0.92 mm. Currently,
65 catheters from four patients were tracked by the EMT
system in combination with the OTS. The deviations of the
implant geometry, determined by this hybrid tracking
approach, are comparable to the previous results,
obtained using only the EMT procedure.
Conclusion
The novel hybrid tracking system allows direct mapping of
EMT and CT data. So far, the system was successfully used
to measure the implant of four patients. The clinical study
is ongoing.
OC-0278 Red-emitting inorganic scintillation detectors
to verify HDR brachytherapy treatments in real time
G. Kertzscher
1
, S. Beddar
1
1
The University of Texas MD Anderson Cancer Center,
Department of Radiation Physics, Houston, USA
Purpose or Objective
Treatment verification during brachytherapy (BT) is
presently limited because only few detectors can measure
accurate and precise dose rates in the steep gradients that
are characteristic for HDR BT. Red-emitting inorganic
scintillation detectors (ISDs) are promising for BT because
they can generate large signal intensities. Furthermore,
they facilitate efficient background suppression because
of the small overlap with the Cerenkov and fluorescence
light contamination induced in the fiber-optic cable (the
stem signal) primarily emitted in blue/green regions. The
purpose of this study was to assess the suitability of red-
emitting ISDs for real-time verification during BT.
Material and Methods
We investigated ISDs based on the 5 inorganic scintillators
ruby, Y
2
O
3
:Eu, YVO
4
:Eu, Y
2
O
2
S:Eu and Gd
2
O
2
S:Eu, of which
the first was rigid and the others in powder form. The ISDs
were compared with plastic scintillation detectors (PSDs)
based on the organic scintillator BCF-12. Each detector
consisted of a 1 mm-diameter scintillator that was coupled
to a 1 mm-diameter and 15 m-long fiber-optic cable.
Optical filters were placed between the ISD volume and
the fiber-optic cable to prevent the stem signal from
striking the scintillator and inducing photoluminescence.
The fiber-optic cable was coupled to a charge-coupled
device camera or a spectrometer to measure signal
intensities and emission spectra, respectively. The
detectors were exposed to an
192
Ir HDR BT source in
experiments dedicated to determine their scintillation
intensities, the influence of the stem signal and
photoluminescence, and time-dependent luminescence
properties.
Results
Figure 1 shows the emission spectra of all detectors (left)
and that the scintillation intensities were up to 19, 44, 16,
54 and 130 times larger than that of the PSD (right). Figure
2 shows time dependent luminescence properties of the
ISDs. The Y
2
O
2
S:Eu and Gd
2
O
2
S:Eu ISDs are not
recommended because their accuracy was compromised
by their time dependence. The scintillation of the ruby,
Y
2
O
3
:Eu and YVO
4
:Eu ISDs changed by +1.6%, -2.8% and
+1.1%, respectively, during 20 Gy, which is the dose that
the ISD inserted in urethra could absorb during a typical
HDR prostate plan. The fluctuation could be reduced to
<0.5% by mixing the Y
2
O
3
:Eu and YVO
4
:Eu phosphors in a
ratio 1-to-10. The stem signal of the ruby, Y
2
O
3
:Eu and
YVO
4
:Eu ISDs was up to 3%, 1% and 2%, respectively, of the
total signal, and the photoluminescence was <1%, when
the BT source moved 8 cm away from the detector and 1
cm from the fiber-optic cable. In contrast, the stem signal
of the PSD was up to 70%.
Conclusion
Red-emitting ISDs based on ruby, Y
2
O
3
:Eu and YVO
4
:Eu are
suitable for HDR BT treatment verification in real time.
Their large signal intensities and emission properties
facilitate accurate detector systems that are
straightforward to manufacture and use which can result
in widespread dissemination and improved patient safety
during BT.
OC-0279 Removing the blindfold - a new take on real-
time brachytherapy dosimetry
J. Johansen
1
, S. Rylander
1
, S. Buus
1
, L. Bentzen
1
, S.B.
Hokland
1
, C.S. Søndergaard
1
, A.K.M. With
2
, G.
Kertzscher
3
, C.E. Andersen
4
, K. Tanderup
1
1
Aarhus University Hospital, Department of oncology,
Aarhus C, Denmark
2
Örebro University Hospital, Department of Medical
Physics, Örebro, Sweden
3
The University of Texas MD Anderson Cancer Center,
Department of Radiation Physics, Houston- TX, USA
4
Technical University of Denmark, Center for Nuclear
Technologies, Roskilde, Denmark
Purpose or Objective
Although in-vivo dosimetry has been available for decades
it is still not a standardized verification tool in
brachytherapy (BT). Major limitations are that in-vivo
dosimeters only provide point dose information and that
the steep dose gradient leads to strong positional
dependency. The aim of this study is to examine whether
it is possible to utilise in-vivo dosimetry for evaluation of
the implant geometry during irradiation in addition to post
hoc dose verification.
Material and Methods
This study includes in-vivo dosimetry measurements from
22 HDR BT procedures for prostate cancer. Needles were
placed in the prostate guided by TRUS with a subsequent