ESTRO 36 Abstract Book

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S94 ESTRO 36
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Conclusion
A new form of BT, MBT, has been proposed, as well as a
promising method of generating optimal treatment plans.
It can be seen that the treatment plans proposed by the
optimiser (NSGA2) deliver satisfactory absorbed dose
distributions to the tumour, whilst sparing surrounding
tissue, which in turn spares more OARs. This method can
be used in real time during clinical treatment of MBT.
References
[1] K. Deb, A. Pratap, S. Agarwal, and T. Meyarivan, “A
fast and elitist multiobjective genetic algorithm: NSGA-
II,” IEEE Trans. Evol. Comput. , vol. 6, no. 2, pp. 182–197,
2002.
PV-0184 Quantitative study on position margin in
Intraluminal Brachytherapy Planning for lung
treatment
C.W. Kong1, H. Geng1, Y.W. Ho1, W.W. Lam1, K.Y.
Cheung1, S.K. Yu1
1 Hong Kong Sanatorium & Hospital, Medical Physics and
Research Department, Happy Valley, Hong Kong SAR
China
Purpose or Objective
In Intraluminal Brachytherapy for lung treatment, a
Lumincath applicator, normally 5F flexible nylon catheter,
is inserted through the Trachea and Bronchus. High
activity radioactive source is loaded through the catheter
for treating the tumor site. Unlike external radiotherapy,
there is no motion control technique for afterloading
brachytherapy treatment. Breathing motion should affect
the position accuracy of Intraluminal Brachytherapy as
both Trachea and Bronchus move with the breathing
motion of the patient. It is not practical for the patient to
do breath-hold during treatment since the whole
treatment can last for several cycles of breathing
depending on the source activity. The additional margin
for treatment length should be considered in Intraluminal
Brachytherapy to compensate such effect. The objective
of this study is to investigate the position margin of
treatment planning on intraluminal brachytherapy for lung
treatment.
Material and Methods
We applied two-dimensional (2D) projection
reconstruction methods to measure the movement of
catheter due to the breathing motion. In 2D projection
reconstruction an orthogonal pair of isocentric
radiographs were taken on the patient inserted with the
Lumincath catheter. By localizing difference position
markers on the catheter in two separate projections, the
catheter can be reconstructed in three-dimensional (3D)
space for the planning calculation. The average position
difference of reconstructed points between two
projections reflects the accuracy of 2D reconstruction
method. By comparing the reconstruction accuracy
between two scenarios: patient doing free breathing and
breath-hold, the impact of breathing motion on the
position of catheter can be derived. In the study an
orthogonal pair of radiographs were done on patients with
free breathing and breath-hold; The discrepancy in the
average position difference between 2D projection
reconstructions with free breathing and breath-hold was
calculated. Such comparsion was done for 12 times on
different patients.
Results
The average position difference between two radiographs
in the breath-hold reconstruction was 1.3 ± 0.5 mm among
different patients. Such difference was greatly increased
to 6.5 ± 2.5 mm in free-breathing reconstruction. Assume
the position difference in the reconstruction due to
breathing motion was independent from other factors such
as isocenter precision and reconstruction calculation
accuracy, the derived average position error of catheter
in the reconstructions due to breathing motion was 6.4 ±
2.5 mm.
Conclusion
Our study showed that in Intraluminal Brachytherapy for
lung treatment, the breathing motion can significantly
affect the catheter position by 6.4 ± 2.5 mm on average.
Position margin of such value should be added in the
treatment length during Intraluminal Brachytherapy
planning to compensate such effect.
PV-0185 Retina dose as risk factor for worse visual
outcome in 106Ru plaque brachytherapy of uveal
melanoma
G. Heilemann 1, L. Fetty1, M. Blaickner2, N. Nesvacil3, D.
Georg3, R. Dunavoelgyi4
1Medical University of Vienna/AKH Vienna, Department
of Radiotherapy, Vienna, Austria
2Austrian Institute of Technology GmbH, Health and
Environment Department Biomedical Systems, Vienna,
Austria
3Medical University of Vienna/AKH Vienna, Department
of Radiotherapy/Christian Doppler Laboratory for
Medical Radiation Research for Radiation Oncology,
Vienna, Austria
4Medical University of Vienna/ AKH Vienna, Department
for Ophthalmology and Optometry, Vienna, Austria
Purpose or Objective
Visual acuity is a common side effect in 106Ru plaque
brachytherapy. The purpose of this study was to evaluate
the retina dose as a risk factor associated with visual
outcome.
Material and Methods
45 Patients treated with 106Ru plaque brachytherapy were
included in this retrospective study. A minimum of 100 Gy
was prescribed to the tumor apex using one of two
available plaque (types CCB, CCA) manufactured by BEBIG
(Eckert & Ziegler, Germany). Treatment planning and dose
calculation was performed using an in-house developed 3D
treatment planning system with Monte Carlo based dose
calculation. Dose volume histograms (DVH) were
generated for both physical absorbed dose and biological
equivalent dose (BED), according to the definition
introduced by Dale and Jones [1]. Visual acuity was
reported using Snellen charts. To analyze potential
predictors in anterior tumor locations, a subgroup of 20
patients was selected presenting with a minimum distance
of 5 mm between tumor and macula. Statistical
calculations were performed in SPSS (version 21, IBM). Risk
factors associated with loss of visual acuity were
evaluated using the Cox proportional hazards models. The
loss of visual acuity was correlated to risk factors using
Pearson correlation coefficients. Statistical significance
was assumed to be p ≤ 0.05.
Results
Median follow-up time was 29.5 months (IQR, 15.0-29.8).
A median apex dose of 131 Gy (IQR, 113.0-150.4) was
delivered to tumors with median apex heights of 4.6 mm
(IQR, 3.5-6.0)), largest basal diameters of 10.8 mm (IQR,
8.3-12.6) and smallest diameter of 9.3 mm (IQR, 7.9-
11.4). The baseline visual acuity (Snellen 0.82 ± 0.23 SD)
was significantly higher (p < 0.001) than the mean visual
acuity at last individual follow-up (0.59 ± 028 SD). The
Pearson Correlation analysis showed a significant