OPTIMIZING LINAC BASED STEREOTACTIC RADIOTHERAPY OF UVEAL MELANOMAS: 7 YEARS CLINICAL EXPERIENCE Kar

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OPTIMIZING LINAC BASED STEREOTACTIC RADIOTHERAPY
OF UVEAL MELANOMAS 7 YEARS CLINICAL
EXPERIENCEKarin Dieckmann Dietmar Georg
Joachim Bogner Martin Zehetmayer Bernhard
Petersch Martin Chorvat Hajo Weitmann Richard
Pötter Department of Radiotherapy Radiobiology
and Ophthalmology, Medical University of Vienna,
Austria
Material and Methods Between 6/1997 and 3/ 2004,
158 pts suffering from uveal melanoma were
treated at a 6 MV LINAC (5x14Gy 5x12Gy
prescribed to 80 isodose). To guarantee
identical pts setup during treatment planning (CT
and MRI) and treatment delivery(Fig.2), pts were
immobilized with a BrainLAB thermoplastic
mask(Fig.1). Eye immobilization was achieved by
instructing the pt to fixate a light source
integrated into the mask system. A mini-video
camera was used to provide on-line information
about the eye and pupil position, respectively.
The new CT and MR compatible prototype, based on
head neck fixation and the infrared tracking
system ExacTrac has been developed and evaluated
since 2002. This system records maximum temporal
and angular deviations during treatment and
based on tolerance limits it gives a trigger
signal online to the linac to interrupt
automatically irradiation in case of deviation of
the actual pupil position compared with planning
pupil position. Fig.4 shows video images acquired
by the eye tracker.The pupil appears as a white
disc, the eye tracker uses infrared illumination
to evoke this bright pupil effect which
facilitaes the digital image processing
responsible for detection of the pupil contour.
The contours can be reloaded prior each treatment
fraction. For treatment planning a 2 mm margin
was used between PTVs and CTVs (Fig 3).
Introduction The collaborative ocular melanoma
study has stated that it is safe to attempt to
preserve an eye with a posterior uveal melanoma
because there is no advantage of enucleation over
local therapy. Melanomas are known to be
radioresistant, thus a high dose is required to
achieve tumor control for this type of tumor. For
more than 30 years episcleral plaque therapy has
been used, utilizing the inherent advantage of
brachytherapy. With this treatment technique
conformal dose distributions are difficult to
obtain for tumors nearby the optic disc, macula
and for very large tumors. Another highly
conformal treatment technique for the management
of uveal melanoma is proton beam therapy. Protons
have a rapid dose fall off in lateral direction
and at the distal part of the beam, allowing to
spare adjacent tissues. Besides these two
traditional treatment techniques, advanced photon
beam therapy techniques have also been applied in
studies to explore their potential for the
treatment of ocular diseases. At the Medical
University Vienna, uveal melanomas have been
treated with 3D stereotactic photon beam therapy
for more than a decade. To optimize the treatment
performance and to guarantee optimal
online-treatment control, different
eye-monitoring systems have been developed. The
present poster summarizes the technical aspects
of linac based SRT of uveal melanoma and reports
on the clinical outcome of more than 150 patients
treated since 1997.
Mask preparation and MRI scanning Fig.1
Target Definition after Image Registration Fig. 2
Results clinical After a median follow-up of
33.4 (3-85) months local control was achieved in
98 (n155/158). Reduced or stable tumor height
after 12 mo. in 88 of the pts 24 mo. 90 36
mo. 90. Fifteen patients (9.0) developed
metastases after a median observation time of 42
mo. (range 11-77 mo.). Secondary enucleation was
performed in 23 pts. (13.8 ). Mean relative
volume- and thickness reduction 12 months 32
volume 24 thickness 24 months
39 volume 29 thickness 36 months
48 volume 40 thickness Side
effects (n158 pts.) Madarosis
6 Bleopharo-conjuctivits
5 Cornea-epithel-defects 3 Cataract
23 Neovascular glaucoma 13.8 Opticopathy
41 Retinopathy
44
Results immobilization Statistical data from
treatments of the first eleven patients is
summarized in table III. Furthermore, total
treatment time (usually around 20 to 25 minutes
for one fraction), net beam-on time (usually
around 5 minutes) and number of automatic
radiation interruptions (if any) have been noted.
Automatic radiation interruptions did occur, an
interruption due to a sudden eye movement of
several degrees magnitude (probably due to
irritation of the patient) during radiation
delivery was only seen once. More frequent but
still rare are interruptions due to slow drift
eye movements away from the reference position.
Stereotactic Radiotherapy Treatment Planning
Fig.3
Patients data male n92
female n66 Involved eye
left n81 right n77 Tumor
thickness 3mm n11
gt3mm n147 Distance 0
mm n51 tumor macula gt 0 ? 3 mm n93

gt3mm n14 Distance 0 mm n4 to
optic nerve gt 0 ? 3 mm n87
gt3mm n31
On-line positioning verification Fig.4
Conclusion Stereotactic photon therapy of uveal
melanoma, based on CT and MRI, is a safe and
precise treatment option. So far, local control
was found to be excellent. The observed side
effects were comparable to other treatment
options for specific cohort considered in the
present study. Automatic surveillance and on-line
control of the position of the eye allows to
perform gated beam delivery for ocular diseases
in a non-invasive manner.