ESTRO 36 Abstract Book

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S194 ESTRO 36
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shifts of 1, 3 and 5mm in both the IN/OUT direction and
2D shifts in both IN/OUT and SUP/INF directions were
introduced.
Results
Fig1b shows the 95% (of 7Gy) dose distribution of the
combined BT and SBRT treatments. Analysis using 2%/2mm
gamma criterion resulted in 99% agreement. Isodose line
matching and a cross profile between measured and
planned doses are shown in Fig1c-d. Fig2 shows the effect
of 1D and 2D isocenter shift on D 98%, D 90% and D2cc metrics
of the CTV. A threshold of +10% was used as a gauge to
compare dose values after shift with the zero shift
baseline. The most changes in dose were for D98% and D90%,
both exceeded the threshold for 3mm shifts and almost
reached -20% for the 5mm shifts.
Conclusion
Using the applicator as a guide, SBRT and BT for cervical
cancer can be delivered on the same day. The isodos e
gradient from BT is used to create dose shells needed to
deliver doses by SBRT. 2D shifts were shown to affect D 98%
the most and a positioning accuracy of 2mm results in dose
variations within +10% from expected.
OC-0362 Precision IORT – image guided IORT in cluding
online CBCT based Monte Carlo treatment pl anning
F. Schneider1, L.D. Jimenez1, F. Bludau2, A. Jahnke1, C.
Illana3, J. Fleckenstein1, S. Clausen1, U. Obertacke2, F.
Wenz1
1 University Medical Center Mannheim, Department of
Radiation Oncology, Mannheim, Germany
2 University Medical Center Mannheim, Department for
Orthopaedics and Trauma Surgery, Mannheim, Germany
3 GMV, Innovating Solutions, Madrid, Spain
Purpose or Objective
The clinical use of intraoperative radiotherapy (IORT) is
steadily increasing based on novel applications like breast
and brain cancer and spinal column metastases.
Traditionally, IORT has been eye and hand guided without
treatment planning and inhomogeneity correction. This
limits the precision of the application and the precise
documentation of the location and the deposited dose in
the tissue.
Kypho-IORT is a novel treatment option for patients with
spinal column metastases in which a minimally invasive
kyphoplasty is combined with a sterilising dose of IORT.
Here we present a set-up where we use image guidance by
intraoperative cone beam CT (CBCT) for precise online
Monte Carlo treatment planning including inhomogeneity
correction.
Material and Methods
During kyphoplasty a working cannula is used to insert a
balloon catheter in the vertebra. The same cannula is used
to insert a x-ray source with a dedicated Needle Applicator
(Carl Zeiss Surgical GmbH, Oberkochen, Germany) to
perform the IORT. For treatment planning an
intraoperative cone beam CT (CBCT) was performed with
the Needle Applicator in place. This CBCT was registered
with a preoperative CT (pre-op CT) in Velocity (Varian,
California, USA). The spinal cord and the metastasis were
contoured on the pre-op CT and the applicator tip was
contoured on the CBCT and transferred to the pre-op CT.
On both CTs the treatment planning was then performed
in Radiance (GMV, Madrid, Spain) using a hybrid Monte
Carlo algorithm simulating dose in homogeneous
(MCwater) and heterogeneous medium (MChet). Dose
distributions on CBCT and pre-op CT were compared with
each other (figure 1).
Figure 1: from top to bottom: dose distribution on CBCT
(MCwater), pre-op CT (MCwater), CBCT (MChet), pre-op
(MChet)
Results
The MCwater calculations showed a spherical dose
distribution as expected. The resulting treatment times
for the prescription of 8Gy in 13mm distance (in water)
from isocenter were within ± 5% of the described
treatment time of the INTRABEAM® system. Due to the