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S192
ESTRO 36 2017
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OC-0361 Commissioning of applicator-guided SBRT
with HDR Brachytherapy for Advanced Cervical Cancer
S. Aldelaijan
1
, S. Wadi-Ramahi
1
, A. Nobah
1
, N.
Jastaniyah
2
1
King Faisal Specialist Hospital and Research Center,
Biomedical Physics, RIyadh, Saudi Arabia
2
King Faisal Specialist Hospital and Research Center,
Radiation Oncology, RIyadh, Saudi Arabia
Purpose or Objective
There is emerging evidence that dose escalation to the
“GEC ESTRO defined” high-risk clinical target volume
leads to improved clinical outcome in patients with
cervical cancer. For those with large residual disease or
with unfavorable topography of parametrial spread,
achieving such high doses is limited by the dose to organs
at risk. Options include a parametrial boost by EBRT which
lack precision and lead to prolongation of overall
treatment time or the addition of interstitial needles
which require a specialized brachytherapy (BT) program.
The option of combining brachytherapy with SBRT, using
the applicator as a guide, is being explored at our
institution. The purpose of this work is to show how this
idea can be successfully implemented using an EBT3
Gafchromic film-based dosimetry system. The effect of
positional inaccuracies on overall dosimetric outcome is
studied as well.
Material and Methods
A cube phantom was constructed to snuggly accommodate
an intrauterine tandem (IU), Fig1a. Pieces of EBT3 film
were taped on both sides of the IU to capture the dose
distribution. The phantom was CT-scanned and the
physician contoured a CTV mimicking large residual
parametrial disease, Fig1b. The plan was such that the
7Gy isodose adequately covers the near-distance CTV. The
BT plan was used as input for the SBRT plan and the 7Gy
to 2.0Gy dose gradient were used to create dose shells,
each having its own dose objective and constraint. Three
VMAT arcs were used to achieve the goal of D
98%
> 95% to
the entire CTV. Later, HDR BT treatment was delivered
using microSelectron v2 and the SBRT was delivered using
TrueBeam®. Positioning accuracy of the phantom was
done using CBCT imaging with the applicator for image
registration. Films were scanned with 10000XL EPSON
scanner at 127 dpi and dosimetry was done using the green
channel and an in-house MATLAB routine. Intentional
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 D
2cc
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 D
98%
and D
90%
,
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. Schneider
1
, L.D. Jimenez
1
, F. Bludau
2
, A. Jahnke
1
, C.
Illana
3
, J. Fleckenstein
1
, S. Clausen
1
, U. Obertacke
2
, F.
Wenz
1
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