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PV-0189 Ring applicator source path determination
using a high resolution ionisation chamber array
M. Gainey
1,2
, M. Kollefrath
1
, D. Baltas
1
1
University Medical Centre, Division of Medical Physics-
Department of Radiation Oncology, Freiburg, Germany
2
German Cancer Consortium DKTK, Partner Site Freiburg,
Freiburg, Germany
Purpose or Objective
Commissioning brachytherapy
applicators can be very time consuming. Brachytherapy
has recently seen efforts to perform array based QA
(Espinoza et al. 2013, Espinoza et al. 2015, Kollefrath
2015, Gainey 2015). Previously we described a technique
for determining one source dwell position per
measurement using the OD1000 (PTW-Freiburg) analogous
to film measurements (Kollefrath 2015). In this work we
employ a time resolved high spatial resolution dose
measurement with OD1000 to determine the entire source
path for each interstitial ring applicator (Elekta AB,
Sweden), available in three diameters (R26, R30, R34),
within a single measurement.
Material and Methods
Two microSelectron (Elekta AB, Sweden) v2 afterloaders
(AL1, AL2) were employed to perform all measurements
with 192Ir. A special PMMA jig consisting of a base plate
and a central insert was constructed to mount onto the
OD1000 array. A time resolved (100ms per frame) dose
measurement of the entire source path within the
respective ring applicator was contrived: a single plan for
each ring diameter consisting of 5.0 s dwell time for each
position (associated source strength 42000U). The
resulting data was analysed using an in-house MATLAB
script (version 8.4.0, The Mathworks NA). Typically three
measurements were repeated for both (blue and green)
clinically commissioned rings and for a number of source
exchanges.
Results
Mechanical uncertainties (type B) of PMMA jig position
relative to OD1000 array were estimated to be 0.2mm.
Repeated measurements with different afterloaders
(without dismantling set-up) are plotted in figure 2. The
maximum standard deviation was found to be 0.6mm for
R26, 0.5mm for R30 ring. A non-linear least squares fit was
made (Gander et al. 1994) to the mean positions R26 and
R30 rings resulting in a radius of 13.2mm and 14.9mm,
geometric centre location of (0.15,0.13) and (0.20,0.10)
respectively.
Conclusion
Initial results indicate that the measurement technique is
robust and reproducible. Repeated measurements with
different afterloaders indicate a maximum standard
deviation of 0.6mm (R26), 0.5mm (R30). Other central
inserts can be devised for other applicators, and
afterloader systems. Thus the technique is versatile but
requires an high resolution 2D array and specialized
measurement jig. Moreover our technique is currently
limited to 2D source path determination viz. in the
measurement plane, parallel to the ring plane.
PV-0190 The analysis of prostate cancer with median
lobe hyperplasia treated I-125 brachytherapy
K. Muraki
1
, H. Suefuji
1
, E. Ogo
1
, H. Eto
1
, C. Tsuji
1
, C.
Hattori
1
, Y. Miyata
1
, H. Himuro
1
, T. Abe
1
, S. Hayashi
2
, K.
Chikui
2
, M. Nakiri
2
, T. Igawa
2
1
Kurume University, Radiology, Kurume, Japan
2
Kurume University, Urinology, Kurume, Japan
Purpose or Objective
Most patients with median lobe hyperplasia (MLH) have a
large-volume prostate and severe dysuria. Prostate cancer
with MLH is a relative contraindication of permanent
prostate brachytherapy (PPB), because of the increased
risk of post-implant urination disorder and the technical
difficulties of stability while implanting intravesical
tissue. We examined that the treatment outcome, seed
migration, urination disorder after treatment in MLH
patients who received PPB. The purpose of our research
concerns is to what degree could MLH implant be
stabilized.