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through MRI at D and at BT. This 3DMD had been developed
by the authors to provide precise reproducible
topographic and quantitative information in one
comprehensive overview (Fig1).
Dimensions of GTV
D
, HR-CTV and IR-CTV for width,
thickness
and
maximum
height
(GEC-ESTRO
Recommendations) as assessed on MRI D/BT (SE T2
weighted sequences) was drawn at all grid levels and in all
3 dimensions as requested in the 3DMD. The cervical canal
was taken as the central axis and the external os
(surrogate for flange) as reference for the various
dimensions.
A qualitative observation was done based on the drawings
of all 42 cases on individual maps. A quantitative analysis
was done with SPSS v20. The dimensions (height, width
and thickness) and volumes were compared and correlated
(n= 42). Thereafter another quantitative analysis of the
widths of GTVD, HRCTV and IRCTV at 0, 1, 2 and 3 cm and
at NMD (Near Maximum distance from the central
tandem/central canal) was done (n=84).
Results
The dimensions of the HRCTV followed closely that of
GTVD, with some variations and exceptions. The IRCTV
volumes were closely overlapping the HRCTV volumes. In
most of the cases the HRCTV and IRCTV were
encompassing the GTVD volumes.
For the detailed quantitative results see table 1.
Conclusion
The advanced schematic 3D mapping diagram provides
precise topographic and quantitative 3D information on
extent of disease and for CTV for BT, using repetitive MRI.
There is a significant correlation of GTVD with HRCTV and
IRCTV in regard to volumes and dimensions. This new tool
may also be used for BT CTV definition based on GE and
CT/US.
PO-0941 Verifying the treatment planning system in
individualized HDR brachytherapy of cervical cancer
M. Van den Bosch
1
, B. Vanneste
1
, R. Voncken
1
, L. Lutgens
1
1
MAASTRO Clinic, Department of Radiation Oncology,
Maastricht, The Netherlands
Purpose or Objective
In state of the art high-dose-rate (HDR) brachytherapy of
the cervical cancer interstitial needles are regularly
placed in addition to the standard applicators to increase
the possibility for dose optimization, i.e. higher tumour
coverage and/or sparing of OAR’s. The use of these
needles enables more individualized treatment plans.
Consequently dose distributions and dose plans have
become highly individualized. As a result, the main output
parameter of the planning system, the total reference air
kerma (TRAK), is more difficult to verify. In this study, it
is investigated whether the high risk clinical target volume
(HR-CTV) can be used to predict the TRAK.
Material and Methods
26 treatment plans of 10 cervical cancer patients were
included in this study. In all patients the titanium Varian
Fletcher applicator was inserted. The number of
interstitial PEEK Varian needles was determined by the
radiation oncologist at the time of the application. T2-
weigthed MR scans were acquired in treatment position
and used for delineation of the HR-CTV, intermediate risk-
CTV (IR-CTV) and organs at risk (OARs). Contouring was
done by the responsible radiation oncologist whereas a
treatment plan was made by the radiation therapist using
BrachyVision (algorithm: TG-43). The calculated TRAK
values of each plan were rescaled to a source strength of
10 Ci and to a fraction dose of 7 Gy (prescribed to the HR-
CTV).
Results