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different fixation systems the mean (M), systematic (Σ)
and random (σ) errors were determined over the patient
population for the intrafraction translations and rotations,
and interfraction rotations.
Results
Figure 2 shows the systematic and random errors of the
intrafraction translations (a,b) and interfraction rotations
(c,d) of the three different fixation systems. Intrafraction
translations were small for all systems, with maximum
deviations generally lower than 1 mm for all fractions, and
a systematic and random error both in the order of 0.3
mm. No statistically significant differences were found
between the vacuum bag and Thermofit system, while the
3D head support showed a slight improvement for the
systematic errors compared to the individually moulded
head supports. Intrafraction rotations were typically in
the order of 0.2
⁰
, and no differences were observed
between the three groups. The systematic and random
errors of the interfraction rotations were in the order of
1
⁰
and 0.6
⁰
for all systems, with no significant differences
between the three fixation systems, and maximum
rotations of up to 4
⁰
were observed occasionally.
Conclusion
Inter- and intrafraction variations were analysed fo r three
different cranial fixation systems. In trafraction
translations were small for all systems, while interfraction
rotations could be significant. The addition of an
individual head support does not seem to decrease the
interfraction rotations, and for intrafraction variations the
results seem to even indicate a slight improvement when
using a standard head support with a shape that provides
good fixation for the head. Individual supports might have
added value for patients with a deviating anatomy.
Poster: RTT track: Imaging acquisition and registration,
OAR and target definition
PO-1001 Evaluation of target volume delineation of
the regional lymph nodes in breast cancer patients
M. Mast
1
, E. Gagesteijn
1
, T. Stam
1
, N. Knotter
2
, E.
Kouwenhoven
1
, A. Petoukhova
1
, E. Coerkamp
3
, J. Van der
Steeg
1
, J. Van Egmond
1
, H. Struikmans
1
1
Haaglanden Medical Centre Location Antoniushove,
Radiation therapy, Den Haag, The Netherlands
2
Leiden University Medical Centre, Clinical oncology,
Leiden, The Netherlands
3
Haaglanden Medical Centre Location Westeinde,
Radiology, Den Haag, The Netherlands
Purpose or Objective
New ESTRO guidelines have been developed for the
delineation of the Clinical Target Volumes (CTVs) of the
regional lymph nodes of the breast. Until now we used the
methods based on the article of ‘Dijkema et al.’. In
response to these new insights, we decided to develop a
tool to implement this new ESTRO guideline. The main
question, which will be answered, is:
“What are the
differences between delineating the regional lymph nodes
of breast cancer according to the method ‘Dijkema et al.’,
‘the ESTRO guidelines’ and ‘the Tool combined with
ESTRO guidelines (‘Tool’)’?”
Material and Methods
In ten patients CTVs of the regional lymph nodes of the
breast were delineated (in Pinnacle [1]) by three
dedicated radiation oncologists, according to the two
different guidelines and the ‘Tool’. The ‘Tool’ is a method
where the subclavian and the axillary vessels are
delineated by a radiation therapist and is expanded in all
directions with 5 mm. This volume is than adjusted by the
radiation oncologist on the basis of the prescribed
anatomical boundaries of ‘the ESTRO guidelines’. After
that, all CTVs were exported to MATLAB to calculate the
Conformity Index generalized (CIgen ) [2]. In MATLAB the
differences in the various directions on the axial coupes of
the treatment planning-Computed Tomography scans
were analysed. Also the volumes of the CTVs were
calculated in Pinnacle. Finally, the required delineating
times per patient, per guideline and per radiation
oncologist were compared and analyses were carried out
using SPSS [3].
[1]: Pinnacle Treatment Planning System, version 9.10
(Philips Healthcare)
[2]: E. Kouwenhoven, 2009,
Phys Med Biol.
[3]: IBM SPSS Statistics for Windows, IBM Corp., Armonk,
NY, USA
Results
The MATLAB analyses showed that the ‘Tool’ had the
highest CIgen (0.64 and σ = 0.05) relative to the other
two methods (
p<0.04
)
(table 1)
. Furthermore, the
delineating time was shortest (13.6 min and σ = 2.4) by
using the ‘Tool’. The use of the ESTRO guideline without
the ‘Tool’ resulted in the smallest average CTV volume
(150.6 cm
3
and σ = 41.0). Furthermore, we saw a clear
decrease of the standard deviations in most delineating
directions when using the ‘Tool’, except in the ventral
direction.
Table 1. The differences of the CIgen between the three
methods.
CIgenDijkema et al. CIgenESTRO CIgenTool
Average
0,58
0,57
0,64
Standard deviation
(σ)
0,05
0,06
0,05
CIgen = Conformity Index generalized
Conclusion
Using the ‘Tool’ we found a significantly higher CIgen and
a smaller CTV volume (compared with the method
'Dijkema et al.'). The advice is to use the ‘Tool’ as