346 / 1082
S331
ESTRO 36 2017
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Results
The DTI analysis was successfully performed pre and post
RT. Differences in FA, RD, and AD between pre and post
RT MRI were assessed. The superimposition of the fiber
tracts maps with the relative information about post
treatment alterations on the dosimetric information of the
simulation CT was finally obtained.
Conclusion
We show the feasibility of a standardized tract-based
dosimetric analysis, potentially useful to establish possible
relations between dose-volumes data and the variation of
DTI indices in WM structures.
PO-0640 Which measurement type should be used for
disease control of brain metastasis, volumetric or
linear?
A. Fischedick
1
, G. Fischedick
1
, U. Haverkamp
2
1
Clemens Hospital, Radiation Oncology, Münster,
Germany
2
University Clinic Muenster, Radiation Oncology,
Muenster, Germany
Purpose or Objective
Which quantification method for disease tracking of brain
metastasis after stereotactic radiosurgery (SRT) is correct,
remains a controversial topic. The RANO-BM standards
involving linear 2d measurement are considered to be the
gold standard. However, 3d measurements are believed to
be more accurate but thorough scientific evidence is still
missing. This study set out to clarify this by analysing 55
patients with brain metastasis before and after SRT.
Material and Methods
Measurements were performed with OsiriX on gadolinium
contrasted T1 weighted MRI images and analysed using
Microsoft Excel. The RANO-BM criteria were applied to the
2d measurements whereas 3d measurements were
categorized according to Matthew J. et al 2012.
Results
This study contained 26 males and 29 females with an
average age of 61 years. The average survival rate post
SRT was 13,9 months categorized into partial responds at
17 months, stable disease at 10,5 months and progressive
disease at 9 months. The categorization for both 2d and
3d measurements were the same in 81,8% of the cases.
However, 18,2% of the 3d measurements were identified
as partial response whereas the 2d measurement placed
them in the stable disease category. In every instance this
could be explained by either weak gadolinium uptake,
cystic morphology or small size of the metastasis leading
to wrong volumetric measurements.
Conclusion
We conclude that the results obtained from 2d and 3d
measurements are highly comparable and that no benefit
from 3d tracking could be observed. Therefore, we
recommend the use of the RANO-BM criteria in 2d linear
measurements for clinical use.
PO-0641 A novel voxel based homogeneity index:
clinical implications for WBRT
A.H. Thieme
1
, C. Stromberger
1
, P. Ghadjar
1
, A. Grün
1
, S.
Zschaek
1
, V. Budach
1
1
Charité-Universitätsmedizin Berlin, Klinik für
Radioonkologie und Strahlentherapie, Berlin, Germany
Purpose or Objective
Homogeneity of a treatment plan is considered to be
important as underdosage may decrease the tumor control
probability and overdosage may result in excess toxicity if
the target volume contains organs at risk. Historically,
homogeneity indices only used a few data points of a dose-
volume histogram (e.g Dmin, Dmax, D5, D95) for
calculation without the possibility to decide if
inhomogeneity arises from under- or overdosage. We have
introduced a novel voxel based homogeneity index (VHI)
which uses the entire information present in the three-
dimensional dose distribution. In contrast to traditional
indices it is possible to determine to what extent under-
and overdosage contribute to inhomogeneity. We analyzed
the performance of the VHI versus traditional indices and
whether VHI results were associated with treatment
outcomes in patients who underwent whole-brain
radiation therapy (WBRT).
Material and Methods
The VHI uses the deviations from the prescribed dose in
each voxel of the target volume to calculate a
characteristic score. The score is without dimension and
independent of the target volume size, fractionation
scheme and prescribed dose. We retrospectively analyzed
patients who underwent therapeutic WBRT between July
2009 and May 2016. VHI results were compared with
results of traditional indices. Overall survival of patients
was assessed and compared with the underdosage part of
the voxel homogeneity index (VHI_Underdosage) using
Kaplan Meier plot analysis and Log-Rank test.
Results
A total of 517 WBRT plans were analyzed. 266 (51.5%) of
patients were male and 251 (48.5%) female. The median
age was 61.5 years, the median prescribed dose was 30.8
Gy and the median number of voxels was 115.137 per
target volume with a resolution of 15.625 mm³ per voxel.
While established indices underestimated inhomogeneity
in certain cases, the VHI showed a significant higher
sensitivity. Differences between radiation technologies
(e.g. VMAT and 3D-CRT) could easily be differentiated
with the new index, while existing indices were not able
to do so. A difference in survival was observed according
to the respective VHI_Underdosage. At the end of the first
year the number of patients who died with an index < 1.9
was 142 (74.3%) compared with 239 (82.7%) with an index
>= 1.9 (p = 0.038 by Log-Rank test).
Conclusion