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Computer Aided Surgery 2:286–291 (1997)
Clinical Paper
VBH Head Holder To Improve Frameless
Stereotactic Brachytherapy of Cranial Tumors
Reto J. Bale, M.D., Michael Vogele, Arno Martin, Thomas Auer, B.S., Emil Hensler, Ph.D.,
Paul Eichberger, B.S., Wolfgang Freysinger, Ph.D., Reinhart Sweeney, B.S.,
Andreas R. Gunkel, M.D., and Peter H. Lukas, M.D.
Departments of Radiology, (R.J.B.), Therapeutic Radiology and Oncology (T.A., E.H., P.E., R.S., P.H.L.),
and ENT (M.V., A.M., W.F., A.R.G.), University of Innsbruck, Austria
ABSTRACT Precise target localization is essential for brachytherapy. We have adapted the VBH
(Vogele-Bale-Hohner) head holder (Wellhoefer Dosimetry, Schwarzenbruck, Germany), originally
developed at the University of Innsbruck, for frameless stereotactic surgery, for use in brachytherapy
of cranial tumors. The VBH head holder allows for rigid, noninvasive head fixation by means of an
individualized upper dental cast. Registration rods, rigidly attached to the dental cast, provide stable
external points of reference. The dental cast is sucked against the upper palate by vacuum, and then
the fixated patient is scanned. During simulation, the targeting device can be positioned with respect
to the virtual patient using the ISG Viewing Wand. Following simulation, the real patient is repositioned under vacuum control, the targeting device repositioned as well, and the actual brachytherapy
initiated.
The VBH head holder is well tolerated by patients and simple to use, and various studies
have confirmed submillimeter accuracy. The modified head holder in combination with a new targeting device allows for precise and well-planned insertion of hollow needles into a tumor using
frameless stereotactic systems as well as being compatible for uses in other fields. Comp Aid Surg
2:286–291 (1997). q1998 Wiley-Liss, Inc.
Key words: stereotactic brachytherapy, frameless stereotaxy, virtual simulation, patient fixation,
VBH head holder, immobilization, VBH mouthpiece
INTRODUCTION
External radiation is the treatment of choice for
inoperable tumors in the ENT region. Owing to
advances in imaging techniques [computerized
tomography (CT), magnetic resonance imaging
(MRI), positron emission tomography (PET), ul-
trasound (US)] and data processing, percutaneous
radiotherapy techniques have improved significantly. Imaging permits accurate measurement of
tumor size and spread. With the aid of computers,
the best possible isodose distribution can be deter-
Received original June 5, 1997; accepted October 31, 1997.
This paper was presented at the German Brachytherapy Meeting, Lübeck, March 5–7, 1997 (Best Poster Award); the
Annual Brachytherapy Meeting GEC-ESTRO, Stockholm, May 5–7, 1997 (Best Poster Award); CAR ’97, 11th International Symposium and Exhibition, Berlin, June 25–28, 1997; and CIS ’97 (Computer Integrated Surgery), Linz, September 1–5, 1997 (Best Poster Award).
Address correspondence/reprint requests to Reto J. Bale, M.D., Universitätsklinik für Radiodiagnostik, Anichstr. 35,
6020 Innsbruck, Austria. E-mail: reto.j.bale@uibk.ac.at.
q1998 Wiley-Liss, Inc.
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Bale et al.: VBH Head Holder for Cranial Tumors 287
mined, thus minimizing radiation damage. Because of the anatomic proximity of essential
structures, minimizing complications and side effects is essential, especially with deeply located
tumors of the head and neck region. Interstitial
radiation allows for application of high doses to
local tumor masses and a more precise distribution of isodoses. The radiation source must be
placed precisely in relation to the tumor volume,
i.e., the tumor center in spherical tumors. In hollow organs, this localization can be controlled by
palpation, but it is difficult to insert the hollow
needles precisely in deeply located soft tissue tumors that are neither visible nor palpable. In these
cases, US and fluoroscopy have been used to
guide the needle. Obviously, they do not provide
the spatial accuracy of 3D CT scans.
For intracranial tumors (primary and recurrent gliomas) stereotactic frames have been used
since the 1980s for accurate insertion of iodine
125 seeds.7,8 The fixation techniques are mostly
invasive, with the stereotactic frame being screwed
into the calvarium.
The Vogele-Bale-Hohner (VBH) head holder1
allows for rigid, noninvasive fixation of the head
by means of an individualized dental cast held
tightly against the upper palate by vacuum. We
have adapted the VBH head holder, originally
developed at the University of Innsbruck, for
frameless stereotactic surgery, for use in brachytherapy.2 To allow for fixation on CT, we have
modified the head holder by replacing metal parts
with carbon fiber or plexiglass. We introduce our
modified head holder and aiming device, which
allows application of frameless stereotactic systems, e.g., the Viewing Wand, for brachytherapy
of cranial tumors.
MATERIALS AND METHODS
Viewing Wand
The Viewing Wand (ISG Technologies, Mississauga, Ontario, Canada) is a frameless stereotactic navigation system allowing for interactive visualization of CT/MRI data from a patient in correlation with the patient’s anatomy during an
operation.12 This system is used for many operations in the head and neck regions. The first step
is to scan the patient by CT or MRI. These 2D
data are reconstructed to three dimensions by an
Allegro workstation and transferred to the Viewing Wand in the OR. The most important step
is the patient’s registration, in which stereotactic
coordinates are correlated with the 3D object (the
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Fig. 1. Plexiglass prototype of the VBH head holder:
1, base plate; 2, neck support; 3, hydraulic mechanical
arms; 4, VBH mouthpiece with hard plastic tube (arrow);
5, counter fixation; 6, shoulder fixation.
virtual 3D object is superimposed on the ‘‘real’’
patient).
A position-sensitive articulated arm, with
six axes of rotation, is used for the registration
and subsequent orientation. At least three points
of reference must be touched by the wand’s tip
and correlated with the 3D object/corresponding
CT slices on the monitor. Once the patient is
registered, the surgeon can place the probe in the
region of interest and follow the actual position
in 2D and 3D views on the monitor at the same
time.
The Modified VBH Head Holder
Figure 1 shows the head holder. It consists of a
base plate, a neck support, three hydraulic arms,
the VBH mouthpiece (VBH MP), and the counter
fixation. The hydraulic arms can be attached to
the base plate (plexiglass plate perforated with
screwholes) and precisely repositioned with plastic screws. The hydraulic arms consist of three
joints giving six degrees of freedom. The three
joints can be immediately blocked by turning one
knob. They also can be positioned in such a way
that they do not overlap with the relevant area and
produce artefacts during imaging. If necessary, all
hydraulic arms can be replaced by carbon fiber
rods and plexiglass cubes. The MP and the
counter fixation cups are attached to the arms.
This setup allows for quick conversion from the
original flexible frame to a rigid frame, thus immobilizing the head of the patient.
The key element of the VBH head holder
is the individualized dental cast. The appropriate
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288 Bale et al.: VBH Head Holder for Cranial Tumors
nation with the metal spheres serves to fix the
target (e.g., the center of the tumor) in space. The
actual targeting device consists of a variable part
and a rigid part connected to each other by metal
screws. The rigid part is attached to the hydraulic
arm and has the diameter of the mechanical Viewing Wand probe, used in the simulation process.
The variable part has an additional drill hole with
the diameter of the actual needle. Thus, the diameter of the hole can be changed as needed by a
revolver mechanism.
Fig. 2. Targeting device: 1, magnetic cup; 2, metal
sphere (with a drill hole to the center); 3, actual targeting
device.
plate is loaded with Impregum F (ESPE, Seefeld,
Germany), a quickly hardening compound consisting of rubber and catalyst. The impression
plate is pressed against the upper palate and removed after 5 min of hardening. Then, a hole is
drilled through the middle of the dental cast and
a 10 1 20 1 1 mm area is cut out. A hard plastic
tube is glued to the hole, and this tube is connected to the vacuum pump. The underpressure,
generated by the vacuum pump, provides exact
repositioning of the dental cast. Finally, the dental
cast is glued or screwed to the upper jaw transverse plate.
The registration rods with the fiducials are
bilaterally connected to the transverse rods of the
mouthpiece at right angles by means of plexiglass
connectors with plastic screws. Length and orientation of the registration rods are variable, depending on the scanned area and the size and
shape of the patient’s head. All three rods and
the upper jaw transverse plate are light and rigid,
being made of carbon fiber. This provides maximal rigidity with minimal weight and an artefactfree CT image. Effective head fixation to the base
plate is achieved by clamping the head between
the upper dental cast and the counter support in
the parietooccipital region.
Actual Procedure
MP Production
An individualized dental cast is prepared in the
manner described above.
Scan
The MP is sucked against the hard palate, generating a vacuum. The registration rods are connected
and the patient is fixated with the head holder
and scanned using a spiral CT 3D protocol. The
patient is then carefully removed from the holder
by detaching the hydraulic arms from the base
plate. To ensure accurate repositioning, the hydraulic arms are left in rigid position until therapy
is completed.
3D Reconstruction and Planning
The 3D object is reconstructed from the CT data
on an Allegro workstation. The tumor is visualized and the target for the hollow needle (center
of tumor) is determined. The optimal target(s) is
determined in advance on the CT slices. The axis
VBH Targeting Device
Figure 2 shows the elements of the targeting device. It consists of the following two components
mounted on the free ends of hydraulic arms: a
magnetic cup with exchangeable metal spheres
(one with a drill hole for the Viewing Wand
probe, the other with a drill hole for the needle)
and the actual targeting device. The cup in combi-
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Fig. 3. Three-dimensional reconstruction of patient
with MP.
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Bale et al.: VBH Head Holder for Cranial Tumors 289
of entrance is defined so that no vital structures
are damaged by needle insertion. Figure 3 shows
a 3D reconstruction of a patient with the MP.
Simulation
For simulation (Fig. 4), the entire frame is repositioned without the patient. After calibration of the
mechanical arm, the virtual patient is registered
using the reference points on the registration rods,
allowing registration in the absence of the patient.
The hydraulic arm with the magnetic bowl on its
end is fastened to the base plate. Then, the target
is determined in stereotactic space using the probe
as viewed on the monitor. The appropriate spot
is stored in stereotactic space by fixating the hydraulic arm with the metal sphere (with a drill
hole to the center). Next, the actual targeting device is mounted on the base plate and the probe
inserted through the appropriate drill hole. Now,
the tip of the probe in the center of the sphere is
always in the virtual target, regardless of the
probe’s direction in virtual space. The search for
the optimal direction of the probe (that being the
path avoiding vital structures between the skin
surface and the target) is conducted using the
Wand’s trajectory 0 and trajectory 90 planes.
Once the appropriate plane is found, the targeting
device arm is fixated and the probe removed.
Then, the hole diameters of the sphere and targeting device are changed to that of the needle
and the needle is inserted. The needle’s length is
stored by attaching a clamp where the needle enters the targeting device. The arms are removed
and the targeting device arm safely stored in this
Fig. 4. Simulation. VBH head holder is repositioned
without the patient. Target point and axis of entrance are
determined in virtual space using the frameless stereotactic system.
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Fig. 5. Therapy. Patient and targeting device are repositioned, the needle is inserted, and therapy is initiated.
position. Sterilization of the needle and targeting
device is performed before therapy.
Therapy
First the patient and then the targeting device
are precisely repositioned. The hollow needle can
now be inserted as far as the clamp allows (Fig.
5), and, after CT control, brachytherapy is initiated.
RESULTS
The Viewing Wand in combination with the head
holder and targeting device has successfully been
investigated and used in our hospital to reach
various structures in the head region on cadavers
as well as intraoperatively in patients.
This method was used for two patients (four
sessions each) with retroorbital tumors who received fractionated brachytherapy. Needle position was evaluated by comparing the respective
control CT slides of the different sessions with
deviations never exceeding 2 mm.
In another study, the trigeminal ganglion
was spiked in five cadavers and three patients and
the accuracy (in the first attempt) evaluated as
follows: in cadavers, removal of the skull, brain,
and dura and subsequent analysis of needle position, and, in patients, fluoroscopy and electrostimulation. Because the foramen ovale has a diameter
of about 3 1 5 mm and the needle is aimed
through its center, a deviation greater than 2 mm
would result in the needle’s progress being halted
by bone.3
DISCUSSION
Conventional brachytherapy is performed by
placing the needles prior to CT, and the therapy
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290 Bale et al.: VBH Head Holder for Cranial Tumors
plan is calculated based on the location of the
needles. If one wants to calculate the dose distribution in advance, placement of the respective
needles must be very accurate.
Stereotactic frames allow for exact placement of needles. These fixation techniques are
mostly invasive, the stereotactic frame being
screwed into the calvarium. Exact repositioning
is hardly possible once the frame is removed. For
fractionated brachytherapy, reproducible placement of the needle is crucial, so reproducible immobilization is a prerequisite.
Noninvasive relocatable frames such as the
GTC repeated stereotactic localizer6 (fixation
with dental impression), the Greitz Bergstrom
head holder,5 and others10 (fixation by mask)
allow for more time between planning and therapy, which is important in more complex cases.
Although we are not aware of literature describing its use in brachytherapy applications, we believe that the only other noninvasive head holder
using the upper dentition for repositioning of even
anaesthetized patients should be discussed. The
somewhat bulky construction of the GTC repeated stereotactic localizer (base frame and
straps) can seriously impede finding the optimal
route of access to the target. It also does not allow
a wide variety of head positioning possibilities.
In vivo repositioning accuracy was measured to
be 0.5 mm (mean), with the maximum displacement being 0.9 mm in an edentulous patient.6
The reported repositioning accuracy of noninvasive mask-based fixation devices is about 2
mm under ideal circumstances.11 The Department
of Radiotherapy/Radiooncology at Innsbruck has
compared the repositioning accuracy of the VBH
head holder to that of thermoplastic mask fixation
using the Philips Easyguide navigation system
on five volunteers. Eight to ten specific external
registration points served as landmarks, and their
positions were compared after each of ten repositionings. System and operator inaccuracy were
also taken into account. Mean VBH head holder
repositioning accuracy (including system and operator inaccuracy) was also 1 mm, whereas that
of the thermoplastic mask was 3.0 mm. (Sweeney
et al., submitted for publication).
In a pilot study in our ENT Department, the
repositioning accuracy of the VBH MP itself was
measured on 50 subjects. In parallel with the accuracy test, the intraoperative success during surgery was evaluated. The results of both the experimental and clinical applications proved reposi-
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tioning accuracy to be in the submillimeter
range.4
To our knowledge, our device is the only
fixation method with permanent repositioning
control. Repositioning accuracy of the VBH head
holder is controlled by the vacuum as seen on a
scale on the pump. If the vacuum does not reach
the desired level (00.8 atm) or suddenly decreases, positioning is inaccurate.
It is necessary, however, to ensure that the
hydraulic arms remain rigidly fixated between
scan and therapy. It is also paramount that the
dental cast with its vacuum chamber be perfect
(i.e., leak-free, or the vacuum will not build up
and repositioning is not confirmed). This might
occasionally require the production of one or two
additional dental impressions (which require
about 20 minutes each). To date, no patients have
complained of pain or tenderness of the upper
palate resulting from the vacuum. No accuracy
measurements for edentulous patients have been
made so far, although repositioning is possible,
and five edentulous ENT patients have had successful frameless stereotactic operations.1 Contraindications for the VBH head holder are loose
teeth and any previous oral surgery or malignancies of the upper palate that interfere with the
vacuum and/or dental impression.
Precise repositioning is achieved in less than
1 min, causing no patient discomfort. Periods of
up to 2 hr were well tolerated by a number of
patients.1 With to the flexibility of the hydraulic
arms, the head can be immobilized in the desired
position.
The same system is compatible for use in
all fields requiring reproducible head fixation
(conformal radiation therapy, brachytherapy,
ENT surgery, neurosurgery, radiosurgery, etc.).
With its performance over the past 3 years, the
VBH head holder has become an important tool
in various departments at our hospital.
ACKNOWLEDGMENTS
We thank Erich Drexel, Philipp Egger, Helmut
Gatt, Dr. Walter Hohner, Reinhard Lins, Christian
Müller, Guido Nieländer, and Walter Spiegel for
technical assistance in constructing the VBH head
holder and targeting device. This work was partially supported by the Oesterreichische Nationalbank under Project No. 5810.
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