Radiosurgery of the head and neck with the world`s first fully

Radiosurgery of the head and neck
with the world’s first fully
robotized 192 Cobalt-60 source
Leksell Gamma Knife Perfexion
in clinical use
Jean Régis, Manabu Tamura, Cécile Guillot,
Xavier Muracciolle, Mariko Nagaje, Denis Porcheron.
Correspondence :
Professeur Jean Régis
Hôpital d'adulte de la Timone,
Service de Neurochirurgie Fonctionnelle
& Stéréotaxique,
264 Rue Saint Pierre,
13385 Marseille Cedex 05
FRANCE
jregis@ap-hm.fr
Radiosurgery of the head and neck with the world’s first
fully robotized 192 Cobalt-60 source
Leksell Gamma Knife Perfexion in clinical use
JEAN RÉGIS, MANABU TAMURA, CÉCILE GUILLOT,
XAVIER MURACCIOLLE, MARIKO NAGAJE, DENIS PORCHERON.
* Stereotactic and Functional Neurosurgery, Timone University Hospital, Marseille, France
** Radiation Oncology Department, Timone University Hospital, Marseille, France.
Object: The world’s first Leksell Gamma Knife® Perfexion™ for radiosurgery of the head and neck became
operational at Timone University Hospital of Marseille on July 10th 2006. In order to strictly evaluate
the new capabilities, advantages, disadvantages and limits of this new technology, patients have been included in a prospective trial. Preliminary results of this trial are presented.
Methods: In 17 working days between July 10th and September 10th 2006, 83 patients were operated by
Gamma Knife surgery in Timone University Hospital of Marseille. Among these, 59 patients were eligible
for the comparative prospective study (informed consent signed, tumoral or vascular indication, no previous radiosurgery or radiotherapy). In accordance with the blinded randomization process 29 patients
were treated with Leksell Gamma Knife 4C and 30 patients with Leksell Gamma Knife Perfexion. Dose
planning parameters, dosimetry measurements on the patients body, workflow, patient comfort, QA procedure and a series of other treatment related parameters are systematically and prospectively evaluated in
both arms.
Results: No technical failures occurred in either arm of the study. The new dose planning system led to the
use of composite shots in 46,7% of the patients. The mean number of different collimator sizes used was
larger with the Perfexion unit than with 4C, 2,23 and 1,57 respectively. The mean number of isocenters
used was lower (10,80 vs. 13,76). The median total treatment time was significantly shorter with Perfexion
(44,5 min vs. 65 min) while the median radiation time was similar in both machines (34,67 min vs. 36,37
min). The procedure was performed using a single run in all the Perfexion cases. With the 4C this was possible in only 37,9% of the cases. Collision risk on the 4C forced us to change the frame gamma angle for
at least one shot in 27,6% of the patients and led to treatment in manual mode for at least one shot in
20,7% of the patients. Collision risk requiring technical adjustment was never observed with Perfexion.
In one patient treated on Perfexion the system required a direct collision check. Compared with the 4C
Perfexion delivers 8.2 times less dose to the vertex, 10 times less dose to the thyroid, 12.9 times less dose
to the sternum and 15 times less dose to the gonads.
Conclusions: This preliminary analysis of our prospective data indicates that procedures with Perfexion
were collision-free even with extreme location of the lesion (e.g. multiple metastases). The duration of the
surgical procedure, duration of nurse, physicist and physician intervention on the machine, and the duration of the QA procedure are all dramatically reduced with the Perfexion unit. Radiation protection, already very good with the Leksell Gamma Knife 4C, is strongly improved with the Perfexion unit. In our
experience, Leksell Gamma Knife Perfexion incorporates technological advances that will contribute to
very significant future progress in head and neck radiosurgery.
KEY WORDS: radiosurgery . stereotactic radiotherapy . vestibular Schwannomas .
arteriovenous malformation . robotisation.
3
FIG 1: The world’s first Leksell Gamma Knife Perfexion installed at Timone University Hospital.
Introduction
In 1951, Lars Leksell introduced the concept of radiosur3
gery. His intention was to create a technique relying on
the use of a large number of converging beams of ionizing
radiation to induce a small volume of necrosis in the target area. After several disappointing attempts using
moving beams, Leksell and Larson created the first fixed
4
source cobalt 60 unit called Gamma Knife. Gamma Knife
5
surgery (GKS) gained worldwide acceptance in the 80's,
together with the emergence of modern imaging, particularly magnetic resonance imaging (MRI) which contributed greatly to improve the safety and efficacy of radiosur2
gery. Development of workstations and planning software enabled three-dimensional radiosurgery planning
with simultaneous calculation of 3D dosimetry and with
3D anatomical imaging reconstruction allowing better
10
control of 3D conformity and selectivity. The addition of
robotic technology (automatic positioning system – APS)
11
improved patient and medical team comfort. In 2002, a
FIG 2: The fixation system is extremely simple and the hidden location of the motors at the rear of the machine leaves a lot of space
for patient positioning and comfort.
4
FIG 3: TLD’s (thermoluminescent dosimeters) are positioned on the
vertex, lens, thyroid, sternum and pelvis on all patients included in
the prospective trial.
group of international experts were asked to define the
requirement specifications for a new Gamma Knife. The
new machine was to be designed such that it matched or
exceeded all the technological and medical requirements
of the very experienced group of experts. The expert
group concluded that the basic principle of multiple con8,12
verging fixed beams and patient immobilization with
the stereotactic frame provided the most reliably precise
and accurate radiosurgical solution. However, in order to
meet future specific indications for stereotactic radiotherapy, a technologically user friendly frameless fixation
solution was also desired. The group agreed on five critical
features: best dosimetry performance, best radiation protection for patient and staff, unlimited cranial reach, full
automation and outstanding patient and staff comfort.
Based on these specifications Elekta Instrument AB developed a completely new radiosurgical instrument which
FIG 4: The original design of the Perfexion. Eight sectors, containing 24 Co60 sources each, are moved by 8 servo drives (see Fig. 6).
Depending on the sector position the collimator size can be 4 (A), 8 (B) and 16 mm (C) or Blocked/off (D).
they humbly named Perfexion. The Marseille Timone
University neurosurgical group was identified as a good
site for a first installation of this extensively revised and
CE marked radiosurgery platform (Fig. 1). In order to
strictly evaluate this new technology and with funding
from APHM (Assistance Publique Hôpitaux de Marseille)
and ethics committee (CPPRB1) approval, we organized a
randomized prospective controlled trial.
Material and Methods
In 17 working days between July 10th and September
10th 2006, 83 patients were operated by Gamma Knife
Surgery in Timone University Hospital of Marseille.
Among these, 59 patients were eligible for the comparative prospective study. These 59 patients were randomized
to undergo Gamma Knife Surgery using either Leksell
Gamma Knife 4C® * in 29 patients or Leksell Gamma
Knife Perfexion® ** in 30 patients.
The goal of this prospective randomized controlled
trial is to identify differences between these two instruments in a population of 200 patients. The study is designed as a controlled randomized comparative prospective
study. Ethics committee (CPPRB1) approval has been
obtained. The study is conducted under the control of the
health authorities. Any severe adverse events will be
reported to these authorities.
Patients eligible are older than 18 years, selected to
undergo Gamma Knife surgery for an intracranial lesion
(vascular or tumoral) with signed informed consent.
Furthermore, eligible patients are not included in any
other trials and have never been treated with radiotherapy or radiosurgery for the same lesion. In women possibility of pregnancy or breast feeding are exclusion criteria.
Irradiation time, treatment time, treatment room occupation time, dose planning parameters, dosimetry measurements on the patients body, workflow, patient comfort,
QA procedure and a series of other treatment related
parameters are systematically and prospectively evaluated
in both arms.
The loading of the 192 Co60 sources of the Perfexion
unit and the reloading of the 201 Co60 sources of Leksell
Gamma Knife 4C were both accomplished after the installation of the new machine. All sources came from the
same supplier and had uniform dose rate. The dose rate of
the machines are very slightly different at 3,628 Gy/min
vs. 3,756 Gy/min.
*, ** Elekta Instrument AB, Stockholm, Sweden
5
Workflow
Workflow evaluation data is summarized in table 1. For
the Perfexion and the 4C the median total time spent by
each patient in the Gamma Knife operating room was
44,5 min vs. 65,0 min respectively and the median “beam
on” time was 34,67 min vs. 36,37 min.
FIG 5: The servo drives. Posterior view of the Perfexion machine,
with the posterior cover removed, showing the servo drives and
the computer system controlling the movements of each sector.
The Procedure
The procedure started with application of the Leksell®
Stereotactic Frame to the patient’s head, under local anesthesia. After frame fixation, MR and CT scans were obtained for dose planning with Leksell® GammaPlan (LGP).
Before every case the MR scanner was calibrated before
examination and the scans verified by comparing them
against the CT images in order to minimize magnetic distortion errors.
Stereotactic angiograms were obtained only for AVM
cases. Based on these images treatment planning (target
localization, definition of boundaries, localization of surrounding radiosensitive structures and dose determination) was performed using the Leksell GammaPlan®
PFX™ release 7.0 and Leksell GammaPlan 4C release
5,34 respectivly for patients treated with the Perfexion
unit and 4C. Patients were positioned in the machine and
the appropriate check procedure performed (Fig. 2).
1,6,13
were
Thermoluminescent dosimetry (TLD) detectors
positioned on the vertex, lens, thyroid, sternum and pelvis
before the start of the procedure (Fig. 3). Leksell Gamma
Knife Perfexion or Gamma Knife 4C procedures proceeded according to the routines of the department and the
patients were discharged within 24 hours after radiosurgery. All procedures were performed by the same neurosurgeon (JR). To secure the reliability of data collection a
dedicated clinical research assistant was in charge of data
collection and management (CG). Before discharge each
patient was asked to complete a brief questionnaire providing their overall judgment about the comfort of the
procedure (scores were good, acceptable or bad for each
question).
Results
Technical Performance
No technical failures were encountered in either arm of
the study and up-time was 100% for the new machines.
6
Dosimetry Technique
With the Perfexion unit the technique for dosimetry has
been significantly modified as compared with the 4C
(Table 2). Comparison of dose planning strategies using
Leksell GammaPlan PFX and Leksell GammaPlan 4C
shows a significant reduction of the number of runs when
using Perfexion. The procedure was performed using a
single run in all the Perfexion cases. With the 4C a single
run was possible in only 37,9% of the cases. The total
number of shots was significantly reduced with a mean
number of isocenters of 10,80 with Perfexion versus
13,76 with the 4C. The mean number of different collimator sizes used in a single patient was larger with the
Perfexion unit (2,23 vs 1,57). With Leksell Gamma Knife
Perfexion it is possible to use hybrid (or composite) shots,
i.e. mixing different collimator diameters in an individual
shot. This allows increased use of shielding and thus
improved protection of critical structures. The new dose
planning system led to the use of composite shots in
46,7% of the patients. The median number of composite
shots used per patient is two. Shielding was used for at
least one shot in only 3,4% of the patients treated with
the 4C and in 50% of the patients treated with Leksell
Gamma Knife Perfexion.
TABLE 1:
A Comparison of workflow parameters on both machines clearly
demonstrates a dramatic time reduction for all phases of the procedure. The total time spent per patient in the Gamma Knife operating
room is very significantly reduced with Perfexion. The
difference in the total “beam on” time differs less between the two
machines. The most dramatic time reduction was related to the
phase of setting the patient up in the treatment room and, to a lesser
extent, to the reduction of the irradiation time.
Time in min
LGK C
median
Standart deviation
Mean dev.
Perfexion
median
Standart deviation
Mean dev.
Total Time in the
Treatment room*
«Beam On»
Time
diff
65
39,98
32,0
36,37
22,28
17,3
26,34
22,80
18,8
Total Time in the
Treatment room
Total
Treatment Time
diff
44,5
37,06
33,90
34,67
27,94
21,60
8,36
13,52
15,29
* From patient installation in the machine to final closure of
shielding doors.
improvement of comfort particularly in terms of comfort
for the shoulders and the back of the patient. A significant
improvement is also noted in terms of anxiety caused by
confinement (claustrophobia).
Body Dosimetry
The results of dose measurements to other parts of the
body are summarized in table 4.
Compared with the 4C unit the Perfexion unit delivers
8.2 times less dose to the vertex, 10 times less dose to the
thyroid, 12.9 times less dose to the sternum and 15 times
less dose to the gonads.
Discussion
We are reporting on the very first experience with a new
radiosurgical instrument developed by Elekta Instrument
AB, the Leksell Gamma Knife Perfexion (Fig. 1). These
preliminary findings are based on the prospective evaluation of 59 patients fulfilling inclusion and exclusion criteria and randomized to undergo radiosurgery using either
Leksell Gamma Knife 4C® or Leksell Gamma Knife
Perfexion® .
FIG 6: The QA system allows real time measurement of the accuracy
in dose delivery. This is a fast and fully automated procedure giving
an immediate result.
Collision Risk
Collision risk is determined before starting the procedure.
Through a “dummy run” it is possible to assess whether
any parts of the stereotactic frame will hit the inside of the
collimator body during the automated treatment. A risk
for collision was predicted by GammaPlan for at least one
shot in 48,3% of the patients treated with the 4C and in
only one patient (3,3%) with the Perfexion. In this single
case a direct check of the absence of collision was required by the system. Collision risk requiring technical
adjustments was never observed with Perfexion. With the
4C collision risk forced us to change the frame angle for
at least one shot in 27,6% of the patients and to use
manual (trunnion) mode for at least one shot in the treatment of 20,7% of the patients.
Until now we have had no instance of collision using
the Perfexion unit. Manual mode treatments are not provided for using Perfexion.
Patient Comfort
The patient evaluation of procedure comfort is summarized in table 3. The questionnaire completed by the patients before being discharged demonstrates a significant
TABLE 2:
Comparison of dose planning strategies on GammaPlan PFX 7.0 &
4C 5,34 demonstrating the significant reduction of the number of
runs (with Perfexion all procedures were completed with a single
run), the significant reduction of the total number of shots, the use
of hybrid (or composite) shots, the increase in the number of different size collimators used in a single patient, the increased use of
shielding for protection of critical structures, the dramatic decrease
of collision risk, the disappearance of technical adjustments required
due to collision risk (no gamma angle change, no trunnion mode
use, no eccentric frame positioning). With Perfexion we have so far
noted complete absence of true collisions.
% of treatment with
1 run composite plug
shot
Angle different
from 90°
Collision
Risk
Trunion
LGK C
37,9
NA
3,4
27,6
48,3
20,7
Perfexion
100
46,7
50,0
0
3,3
NA
LGK C
run
shots composite shot collimatorused Trunion**
Median
2
12
2,48 13,76
Mean
Standart deviation 2,05 11,44
Mean dev.
1,4 9,3
Perfexion
run
per run*
0
0
0
0
2
1,57
0,50
0,5
2
4,5
2
3,25
shots composite shot collimator used Trunion**
Median
1
10
1,00 10,80
Mean
Standart deviation 0,00 7,28
0,00 5,99
Mean dev
per run*
2
1,77
0,87
0,71
2
2,23
0,82
0,70
NA
* ”Composite shots per run” is the number of hybrid shots in those patients in
whom at least one hybrid shot was used.
** This is the number of shots done in trunnion mode in those patients treated with at least one shot in trunnion mode. Trunnion mode means manual
setting of the coordinates.
7
FIG 7: Treatment of eccentrically located lesions. Dose planning on the same day of 4 brain metastases in extreme and opposite locations
(frontal anterior, far lateral and posterior fossa) with no collision concern, few constraints on frame positioning and no requirement for technical adjustments, e.g. changing of frame angle, trunnion mode etc. Note that each lesion is treated very easily with a single isocenter. In order to
shape the dose plan to make it fit with the lesion, two shots are hybrids (mixing 8 and 16 mm collimators) and one shot has three sectors
blocked (72 beams).
Preservation of Fixed Converging Beams Design
The preservation of the multiple fixed converging beam
design of Leksell Gamma Knife Perfexion gives this system the advantage of being able to rely on the very large
and prolonged worldwide clinical experience gained to
date, as well as on the thousands of peer-reviewed papers
published by teams operating their patients using Leksell
Gamma Knife.
Specific Perfexion Design
The original design of the Perfexion unit is based on a
single, integrated permanent collimator system that incorporates openings for collimators of 3 different diameters
(Fig. 4). The collimators are partitioned into eight segments around the circumference of the device, each containing an independently moveable sector. These eight sectors, each containing 24 Co60 sources, are operated by
individual servo drives (Fig. 4 & 5). Depending on the sector position the collimator size of each sector can be individually varied between 4, 8 and 16 mm or be blocked
(off) (Fig. 4).
8
Complete Automation
The design of the Perfexion allows full automation of the
whole surgical procedure. Both beam configuration and
coordinate settings have been automated which greatly
alleviates the workload of the staff.
Beam Off
The beam off position, which is possible independently in
each one of the eight sector, significantly increases flexibility in beam shaping thus increasing the possibilities when
protection of surrounding critical structures becomes
important. Also, and importantly, the possibility to turn
off all the beams allows changing of the x, y and z coordinates without moving the couch and the patient out of
the machine. These are the steps in the procedure where
Perfexion saves the most time. With the 4C unit, moving
the couch in and out of the radiation unit in order to reposition for a new shot takes 30 seconds per shot and each
time the collimator needs to be reconfigured takes an
additional approximate 10 minutes. With the Perfexion
unit this time has been reduced to almost zero.
FIG 8: Dose planning using dynamic shaping in a patient presenting with a secreting pituitary adenoma (growth hormone). The patient was
previously operated but still presents with aggressive disease. The dynamic shaping process was initiated after a very conformal and selective
dose plan had been produced. Dynamic shaping allowed a further significant reduction of dose to the visual pathways. A dose of 25 Gy at the
50% isodose was selected. This is a rather high dose at this location and for a lesion of this size (3300 mm3). A level 2 setting for sensitivity of
the dynamic shaping process was sufficient to obtain an acceptable dose to the visual pathways (less than 8 Gy) Note the flexibility of the dose
planning and the versatility of the solution developed for each shot. With just 14 shots we were able to obtain a very conformal plan. Darken
Shaded sectors are blocked as an effect of the activation of the dynamic shaping process (in two critical shots). Among the 14 shots only one is
a full collimator (8 sectors at 4mm). In 10 shots between 1 and 4 sectors were blocked in order to better adapt the shot to the anatomy (taking
into account both the lesion itself and surrounding critical structures). Six out of fourteen shots were mixed.
Limitations
There are some potential limitations with the Perfexion
unit. The system is designed in such a way that a manual
treatment mode is no longer possible. This is probably a
relative limitation given the extensive testing that went
into the verification of the design. In our experience the
reliability of the device is remarkable. In our center this is
definitely of no concern since we have both systems working in parallel. The sector system is a technological choice
with a lot of virtues but also one theoretical limitation
which is that limited plugging of only a handful of beams
is no longer possible. In practice so far we have been indifferent to this theoretical limitation. The design with plugging of entire sectors (24 sources) has turned out to be
very well adaptated to the task of protecting surrounding
critical structures. Full robotization means no direct
human checking of coordinate settings or collimator selection for each shot.
TABLE 3:
Patient comfort during the procedure. A questionnaire completed
by the patients before discharge shows a significant improvement of
comfort, particularly in terms of strain on shoulders and back as
well as anxiety related to confinement (claustrophobia).
Rating
Overal The site
experience
Shoulder
Back
Claustrophobia
LGK
% Good
% OK
% Bad
67,9
28,6
3,6
100,0
84,0
8,0
7,1
99,1
71,4
25,0
3,6
100,0
64,3
25,0
10,7
100,0
78,6
17,9
3,6
100,0
% Good
% OK
% Bad
70,4
29,6
0,0
100,0
95,8
4,2
0,0
100,0
88,9
7,4
3,7
100,0
85,2
11,1
3,7
100,0
85,2
7,4
7,4
100,0
PFX
9
Quality Assurance System
The QA system of the Perfexion unit allows direct measurement display of the dose delivery diagram in real time
(Fig. 6). This is a real advantage and an important improvement of the QA procedure.
User Friendliness
Ease of use is the first obvious advantage of this device
over all pre-existing radiosurgical systems. When dose
planning is finalized and the plan has been exported to the
treatment machine only a few minutes of work remain for
the physician. The treatment is performed using a single
run and patient positioning in the machine is extremely
simple (Fig. 2). When treatment planning has been completed and the plan exported only three task remain before
initiating the procedure on the Perfection:
1.
To position the patient on the couch in a way that
optimizes patient comfort
2.
To connect the head frame to the couch
3.
To check and confirm patient identity using a single
button
4.
Couch and patient are no longer moving in and out
of the machine. This is appreciated by the patients
and significantly reduces total treatment time.
5.
Radiation outside of the treatment machine has been
reduced to a level so low that we have been allowed
to separate the treatment and control rooms with just
a large window of ordinary glass (Fig. 9). Patients no
longer have the unpleasant feeling of being completely
isolated. They can see the staff and their family
through the window. This is a real contribution to the
psychological comfort and well-being of the patient.
6.
Anxiety caused by confinement (claustrophobia) has
been much reduced in the new machine, largely due
to the important increase of space inside the collimator body.
Collimator Size
The size of the collimator body in Perfexion is three times
larger than the previous collimator helmets. This is a
major change that has four main positive consequences:
Alltogether these three steps require a few seconds.
1.
Patient Throughput
Speed of patient throughput is very much improved
(Table 1). The reduction of the total treatment time is
mainly related to 4 factors:
The risk for collision is dramatically reduced or entirely removed. This in turn has obviated the need for
eccentric frame positioning thereby increasing patient
comfort.
2.
Classical indications for radiosurgery in peripheral
locations such as around the foramen magnum or
ophthamological conditions are now easily and comfortably treated.
3.
Multifocal lesions such as multiple metastases are
easy to treat in a single run even if very excentrically
located (Fig.7). Trunnion mode is no longer needed
nor is frame repositioning, consequences which bring
tremendous time savings.
4.
Extended reachability to head and neck areas previously unreachable will soon lead to a major expansion
of radiosurgical indications. Lesions in and around
the paranasal sinuses, the orbits, the cervical spine
and the pharyngo-laryngeal area are now accessible.
A specific fixation device for head and neck lesions is
under development.
1.
All patients are treated in a single run
2.
Full automation has made all manual interference
redundant
3.
The full off position enables coordinate resetting
without withdrawal of the couch
4.
Patient positioning and initiation of treatment are
three extremely easy and swift steps
Patient Comfort
Patient comfort has been greatly improved as illustrated
by the summary of patient questionnaires (Table 3). We
can identify at least 6 major reasons for this.
1.
The motors driving the system are no longer located
in the patient space but have been integrated in the
core of the machine, thereby significantly improving
the space around the patient’s body and shoulders.
2.
The inside of the collimator body being three time
larger than the previous collimator helmets of the 4C,
there is much less need for eccentric frame positioning. Such frame positioning can sometimes be quite
unpleasant for the patient.
3.
Positioning of the surgical target at the point of beam
intersection is accomplished by moving the couch
around that point. There is no longer any tension or
stress exerted on the neck of the patient.
10
Extended Anatomical Reach
Head and neck extended reachability will in the near future lead to a major enlargement of radiosurgery indications. The new adaptor for frames which is located on the
top end of the couch is very versatile and has been designed to welcome a new family of different frames intended
for different applications. One of the first frames of this
family under development is a fixation device for cervical
spine lesions. A repositionable frame dedicated for stereotactic radiotherapy is also expected. Flexibility in Dose
Window
A
B
C
D
FIG 9: Timone Hospital installation of the Perfexion in the special operating room. Note the window in floorplan (A) which was made possible
by the very low amount of leakage radiation with the Perfexion. Measurements are given at 1 m above floor before loading of the sources (B)
in beam off state (C) and beam on state (D). The spacing of the grid is 0.5 m. No other horizontal plane contains dose rates higher than this
plane. Dose rates are in µSv/h. Dose rates in locations with no specified value are less than 2 µSv/h.
11
Planning
Dose planning is gaining flexibility with the sector philosophy. The major dose planning changes in practice are
related to three factors:
1.
Complete automation allows the use of as many collimators as desired without any manual interaction.
2.
Shielding no longer requires manual work. The
increases the use of plugging which will lead to further refinement of treatment plans.
3.
The new possibility to create hybrid isocenters (also
called composite shots) provides new flexibility in
sculpting single shots both by relying on the use of
plugging and by mixing different size collimators
(Fig. 8). Conventional planning using 4, 8, and 16
mm collimators is done very similarly on both
GammaPlan PFX and GammaPlan 4C. The two
GammaPlan platforms are very similar in this respect
and a classic multi-isocentric plan7 can be done with
little training. However, the moving sector principle
of Perfexion is opening the field to hybrid isocenters
which is very new and will require more training.
Body Dosimetry
Dosimetry on different parts of the body during the procedures has been shown to be particularly satisfactory in
Gamma Knife radiosurgery as compared to alternative
13
radiosurgical techniques. Radioprotection is increasingly
considered as a major and important aspect of radiation
medicine. The majority of patients operated with radiosurgery are presenting with a benign condition and a rather normal life expectancy. Measurements in the
Perfexion operative room are extremely low (Fig. 9).
Radiation during patient couch transit have been reported
as contributing little to the doses at the measured extra
9,13
cranial sites. However, the increased robotization and
automation of the Gamma Knife has led to a dramatic
increase of the number of isocenters used and thus to a
11
slight increase in transit dose. In Perfexion this has been
addressed by incorporation of the all beams off feature
(Fig. 4). Also, the more liberal use of plugs has been said
to increase the extra cranial dose.1 Our preliminary comparative dosimetry measurements have demonstrated a
significant reduction of the dose delivered to the body.
This is preliminary analysis of our initial experiences.
It will require further confirmation with more extensive
experience and additional evaluation of the impact of the
Leksell Gamma Knife Perfexion. Long term clinical outcomes remain the most important factor for clinicians in
their assessment of new technologies. Nevertheless, the
preservation of the converging fixed beams design allows
us to be very confident in the continued high quality of the
long term clinical outcomes achieved so far with Gamma
Knife surgery.
12
TABLE 4:
Median dose measured on the body (the vertex, thyroid, sternum
and gonads), both in patients treated with the Perfexion and those
treated with the gamma Knife 4C, demonstrating a dramatic reduction of the doses delivered to these structures in patients treated on
the Perfexion. Perfexion is delivering 8.2 times less dose to the vertex, 10 times less dose to the thyroid, 12.9 less dose to the sternum
and 15 times less dose to the gonads. The values relative to the lens
will be presented in a future paper.
Perfexion
LGK 4C
vertex
3026507
Median 2701427
St dev 2116051
thyroid
853270
668207
665419
sternum
424043
257955
416464
gonads
173147
47120
340456
Mean
Median
St dev
Factor
8546115
8475738
5887574
10,0
5479509
5183195
3715282
12,9
2590071
1686158
2474649
15,0
24766524
29673594
14305340
8,2
Conclusions
In this preliminary experience Leksell Gamma Knife
Perfexion is turning out to represent a great improvement
other radiosurgical technologies and even over earlier
Gamma Knife systems. We have been able to verify that
Perfexion fulfills all requirements submitted by the Expert
Group while also preserving the operational characteristics and identity of Gamma Knife which have made it the
gold standard radiosurgery instrument for decades. The
workflow improvement has surpassed all expectations.
Fully integrated robotization is giving more freedom to
the dose planning process and is even creating new opportunities for further dose planning refinements with hybrid
shot availability. The dramatic increase of the treatable
volume by over 300% is already improving patient and
staff comfort and is also expected to expand greatly radiosurgery's role in the head and neck and cervical spine
areas. Our overall feeling is that this new generation of
platform for radiosurgery is a real quantum leap for
radiosurgery technology and appears to make radiosurgery
even easier, faster and safer than before. However, longer
follow up and more extensive experience is required before
drawing any kind of definitive conclusions. We may well be
looking at the dawn of a new era for radiosurgery.
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