Computer Aided Surgery
ISSN: 1092-9088 (Print) 1097-0150 (Online) Journal homepage: https://www.tandfonline.com/loi/icsu20
Staged image guided robotic radiosurgery for optic
nerve sheath meningiomas
Pantaleo Romanelli, Livia Bianchi, Alexander Muacevic & Giancarlo Beltramo
To cite this article: Pantaleo Romanelli, Livia Bianchi, Alexander Muacevic & Giancarlo Beltramo
(2011) Staged image guided robotic radiosurgery for optic nerve sheath meningiomas, Computer
Aided Surgery, 16:6, 257-266, DOI: 10.3109/10929088.2011.622615
To link to this article: https://doi.org/10.3109/10929088.2011.622615
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Computer Aided Surgery, November 2011; 16(6): 257–266
CLINICAL PAPER
Staged image guided robotic radiosurgery for optic nerve sheath
meningiomas
PANTALEO ROMANELLI1, LIVIA BIANCHI1, ALEXANDER MUACEVIC2,
& GIANCARLO BELTRAMO1
1
CyberKnife Center, Centro Diagnostico Italiano, Milan, Italy; and 2European CyberKnife Center, Munich, Germany
(Received 5 April 2011; accepted 30 August 2011)
Abstract
Objective: Optic nerve sheath meningiomas (ONSMs) represent the most challenging lesions involving the optic pathways:
Microsurgery is not indicated and classical single-stage radiosurgery appears to be too risky due to the expected destruction
of the common blood supply with consequent loss of vision. Staged radiosurgery might be one treatment option because it
exploits the ability of normal tissues to repair sub-lethal radiation-induced damage, offering a chance to control tumor
growth while sparing function. Staged robotic radiosurgery was offered to 5 patients harboring ONSMs with the aim of
sparing vision while achieving local growth control.
Patients and Methods: Five patients with ONSM presenting with visual field deficits and loss of visual acuity were treated
with staged CyberKnife radiosurgery, receiving 20 Gy in 4 stages (5 Gy per stage). Treatment planning was based on
contrast-enhanced thin-slice CT (1.25 mm thickness for the first three cases, 0.5 mm for the last two) and volumetric MR
imaging (1.5 T for the first three cases, 3 T for the last two). An interval of 24 hours was strictly observed between stages.
Visual acuity and visual fields were assessed in all patients immediately prior to treatment and at intervals of 6 months
thereafter. Follow-up MRIs were performed every 6 months for 2 years, then once per year.
Results: The entire procedure, inclusive of imaging, treatment planning and treatment delivery, was performed in 5 days.
Irradiation required approximately 45 min per stage. Mean tumor volume was 2.94 cc (range: 0.8–6.4 cc). Treatment was
well tolerated in all patients. Follow-up ranged from 36 to 74 months. Local growth control was achieved in all patients.
Restoration of normal vision was experienced by 4 patients 6 to 12 months after the treatment. One patient, who was also
affected by diabetic retinopathy, showed a modest improvement after 6 months, remaining stable thereafter.
Conclusion: Staged CyberKnife radiosurgery provides a fast and well-tolerated non-invasive treatment with excellent visual
outcomes. If these preliminary results are confirmed by larger series, staged radiosurgery could be proposed as a first-line
treatment for ONSM.
Keywords: Radiosurgery, staging, optic nerve sheath meningioma, CyberKnife, image guidance
Introduction
Optic nerve sheath meningiomas (ONSMs) are rare
lesions, representing approximately 1 to 2% of all
intracranial meningiomas, but their origin and
location make them one of the most demanding
treatment challenges in neurosurgery. Primary
ONSMs originate from the meningeal sheath of the
orbital or canalicular segment of the optic nerve.
Secondary ONSMs have an intracranial origin and
invade the orbit, compressing and displacing the
optic nerve. This paper reports a new treatment
option for primary ONSM and will therefore refer
exclusively to this entity. Primary ONSMs share the
same pial blood supply as the optic nerve itself: both
microsurgical resection and stereotactic irradiation
are therefore likely to injure the nerve’s blood supply,
leading to blindness. ONSMs are most commonly
found in middle-aged women, but may also occur in
children with neurofibromatosis type II, in whom
Correspondence:
Dr. Pantaleo Romanelli, CyberKnife Center, Centro Diagnostico Italiano, Via Saint Bon 20, Milano 20147, Italy.
E-mail: radiosurgery2000@yahoo.com
ISSN 1092–9088 print/ISSN 1097–0150 online ß 2011 Informa UK Ltd.
DOI: 10.3109/10929088.2011.622615
258
P. Romanelli et al.
they display a more aggressive growth pattern sometimes involving both optic nerves. They are typically
detected when patients present with mild proptosis
or progressive, painless loss of visual acuity or visual
field, most often peripheral constriction. Their
growth pattern has classically been viewed as
typically circumferential along the optic nerve,
although it is not uncommon to find lesions
displacing the nerve peripherally (this could be an
initial stage of the disease, followed over time by
encasement of the nerve). The symptoms are those of
a compressive neuropathy and include, in the early
stages, dyschromatopsia and afferent pupillary
defects. At the time of diagnosis the patients present
with more or less marked visual field deficits,
reduced visual acuity, and optic disc edema. Over
time, ONSMs may extend through the optic canal
intracranially. Optic chiasm involvement with bilateral visual deficits may be caused by direct extension
or by traction and distortion of the chiasm. In later
stages, optociliary shunt vessels and marked proptosis are detected. Computed tomography (CT) and
magnetic resonance imaging (MRI) show typical
findings of thickening of the optic nerve, sometimes
accompanied by calcification within the tumor.
ONSMs appear as contrast-enhancing lesions encasing (Figure 1) or compressing and displacing
(Figure 2) the optic nerve. 3-T MRI provides
Figure 1. Case II. Axial (a), coronal (b) and sagittal (c) gadolinium-enhanced T1 MR sequences show an atrophic but
clearly visible right optic nerve encased by a globular contrast-enhancing homogeneous lesion. The axial cut shows well the
perineural growth pattern typical of ONMS, while the entire intraorbital course of the nerve can be appreciated. The same
lesion appears on CT imaging [illustrated here in the context of the treatment plan (d)] as a large contrast-enhancing lesion
encasing the right optic nerve.
Staged image guided robotic radiosurgery for optic nerve sheath meningiomas
enhanced definition of the nerve (Figure 3), allowing
better resolution of the nerve-tumor spatial relationship and optimization of the radiosurgical treatment
planning.
Because of their intimate relation to the optic
nerve and their sharing of a common pial blood
supply, ONSMs present a rather unique treatment
challenge. Their typically slow development and
the high morbidity of microsurgical resection
have encouraged a conservative, watch-and-wait
approach. However, progressive deterioration of
vision over time has been reported in approximately
85% of patients with prolonged follow-up [1–3],
while long-standing visual deficits are less likely to
be reversed by treatment. Microsurgical resection is
usually reserved for patients with a long history and
near-complete or complete loss of vision in the
affected eye. Even in very experienced hands,
blindness typically follows microsurgical resection
of ONSMs [4–6].
Conventional radiotherapy, either as an adjuvant
to surgery or alone, has been shown to be
Figure 1.
259
moderately effective and reasonably well tolerated;
an early review of published studies with a total of
12 patients by Dutton [1] indicated improvements
in visual acuity in 75% of patients. Radiationinduced neuropathy and retinopathy, dry-eye syndrome and various adnexal complications have been
described, particularly when doses higher than
54 Gy and high fractional doses (1.9 Gy or higher)
are used [7].
A more conformal technique developed in the last
decade, stereotactic fractionated radiation therapy
(SFRT), has been successfully applied to the
treatment of ONSMs [8, 9]. Primary SFRT has
preserved vision in patients with ONSM better than
observation alone. Based on its safety and efficacy,
and concerns about injury from single-session SRS,
SFRT has been proposed as a standard treatment
approach for ONSM. Nevertheless, residual dose
spillage over the retina and other nearby structures
has occasionally led to loss of vision due to radiation
retinopathy or vascular occlusion of retinal vessels.
Long-term ophthalmic, adnexal and peripheral
Continued.
260
P. Romanelli et al.
Figure 2. Treatment planning for patient I. CT imaging shows a contrast-enhancing globular lesion growing eccentrically
to the left optic nerve, which is compressed and displaced. Treatment planning details such as dose delivered and DVHs
are illustrated.
complications secondary to conventional irradiation
or SFRT have been reported and include iritis,
temporal lobe atrophy and endocrine failure [10, 11].
Optic neuritis has been also described following
SFRT [12].
Stereotactic radiosurgery involves the precise
delivery of a very high dose of radiation with the
goal of ablating a small-to-medium-sized intracranial
target, with sparing of nearby structures. While
SFRT relies on a combination of tissue sparing and
daily fractionation to protect the optic nerve, radiosurgery provides extremely tight dose distributions
and conformality, restricting the irradiation to the
tumor and offering the highest degree of perilesional
tissue protection, with an unchallenged 80 to 20%
dose fall-off within 3 mm of the target. Frame-based
radiosurgery requires drastic measures for the
immobilization of the patient and accurate targeting
of the lesion, with the entire treatment being typically
delivered in a single session, or stage, of 12 to 14 Gy:
this dose greatly exceeds the tolerance of the optic
nerve [13]. The advent of frameless image-guided
radiosurgery in recent years offers the chance to split
the radiosurgical dose into several fractions (usually
two to five) while keeping the highest degree of
conformality and accuracy. The Stanford University
group pioneered the novel use of staged radiosurgery
for the treatment of optic pathway lesions [14, 15].
Based on this experience, staged radiosurgery has
been applied to the treatment of ONSM using a
fractionation protocol [16].This study describes five
patients with primary ONSM treated using a robotic
image guided radiosurgery system and the functional
outcome of this treatment based on periodic assessment of visual fields and acuity.
Patients and methods
Patients
Five patients (4 female, 1 male) ranging in age from
28 to 64 years (mean: 47.2 years) with a diagnosis of
Staged image guided robotic radiosurgery for optic nerve sheath meningiomas
261
Figure 3. CyberKnife radiosurgery treatment planning for a right ONSM. This patient was a 28-year-old female
presenting with progressive deterioration of visual fields and acuity in the right eye over the previous 6 months. (a) Optic
nerve imaging was performed using 3-T MR (Siemens Trio). CT-MR fusion was performed on the CyberKnife treatment
planning station. The nerve was identified as a loop displaced downward by the tumor and was drawn as a critical structure.
This enhanced the degree of nerve sparing from irradiation. (b) A total of 109 beams were delivered non-isocentrically to
the lesion. Treatment volume was 0.764 cc. A total dose of 20 Gy prescribed to the 70% isodose was delivered in 4 stages
(with 5 Gy per stage) separated by an interval of 24 hours. Maximum dose was 28.57 Gy. Tumor and optic nerve dose
volume histograms (DVHs) show a substantial sparing of the optic nerve.
primary ONSM were treated with staged CyberKnife
radiosurgery. Patient and treatment characteristics
are summarized in Table I. The first three patients
have already been discussed in a previous report [16];
the current paper provides a larger series with a much
longer follow-up period. The interval between onset
of symptoms and treatment ranged from 6 months to
4 years. Slow worsening of vision characterized all
the cases (except for patient V, presenting with
sudden deterioration). No detectable growth of the
tumors was noticed on serial imaging. All the patients
retained a degree of residual vision in the affected
eye, while patient IV could only see through the
affected eye, having lost vision in the other eye years
before due to diabetic retinopathy. Surgery was not
offered to these patients to avoid loss of vision in the
affected eye (or total blindness in the case of
patient IV).
Diagnosis of primary ONSM was based on
clinical history (visual complaints such as peripheral
constriction of visual fields, reduced visual acuity,
proptosis or frank exophthalmos) and orbital
imaging showing findings typical of ONSM. Open
biopsy was not performed. The tumor involved the
orbital segment in 4 cases and the canalicular
segment in one (patient III).
Each patient was affected by campimetric deficits
(bilateral in three, unilateral in two). In the three
patients (I, II and IV) with bilateral field deficits, the
side affected by the ONSM showed much more
pronounced involvement in two cases (I, II), while
the other (IV), affected by long-standing type I
diabetes and concomitant bilateral retinopathy,
came to observation with the eye affected by the
ONSM retaining serviceable vision while the other
eye was almost blind. Visual acuity was impaired in
262
P. Romanelli et al.
Figure 3.
Continued.
Table I. Patient and lesion characteristics, treatment parameters, outcome and follow-up duration.
Gender
Optic nerve
Location (segment of ON)
Visual acuity at time of treatment
Interval from diagnosis to treatment (mo)
Treatment volume (cc)
Presenting symptoms
Dose/isodose %
Dmax (Gy)
Total ON dose (Gy)
ON dose per fraction (Gy)
Post-treatment visual improvement
Follow-up (mo)
F
M
F
F
F
Left
Orbital
20/30
12
2.8
VFL
20 Gy, 83%
28.9
10
2.5
Yes
88
Right
Orbital
20/40
36
6.4
Exophthalmos, VFL
20 Gy, 80%
25
20
5
Yes
80
Right
Canalicular
20/40
24
1.1
VFL, VAL
20 Gy, 72%
27.7
10
2.5
Yes
78
Right
Orbital
20/40
36
3.6
VFL, VAL, proptosis
20 Gy, 70%
28.6
8
2
No
39
Right
Orbital
20/30
6
0.8
VFL, VAL
20 Gy, 70%
28.6
8
2
Yes
36
ON: optic nerve; VFL: visual field loss; VAL: visual acuity loss.
all patients: patients I and V presented with 20/30
vision while patients II, III and IV presented
with 20/40. Two patients (I, IV) also presented
also with proptosis and one (III) with severe
exophthalmos and optociliary shunt vessels.
Radiosurgical treatment was performed within 6
months (I) to 4 years (IV) from the onset of
symptoms.
Procedures
The first three patients underwent a contrastenhanced, thin-sliced (1.25 mm) CT scan and a
volumetric contrast-enhanced 1.5-T MR study
(complemented by T1, T2, FLAIR and PD
sequences inclusive of axial, coronal and
sagittal cuts). The last two patients were studied
Staged image guided robotic radiosurgery for optic nerve sheath meningiomas
263
Figure 4. Visual fields before and after treatment for patient I. The upper row corresponds to the left eye, the lower row to
the right eye. On each row, the first box is the visual field pre-treatment, the second box is the field after 6 months,
and the third box is the field after 1 year. This patient maintained stable visual fields thereafter, with follow-up now
approaching 8 years.
using 0.5-mm thickness CT and 3-T MR. A 20-Gy
total dose was prescribed to the 70% isodose line
and delivered in 4 fractions of 5 Gy each. The
inverse planning system was instructed to keep the
maximum dose below 30 Gy (mean: 27.76 Gy;
range: 25–28.9 Gy). The targets were identified on
the fused images; however, the contouring of the
target and of the critical structures was performed,
when possible, on the CT volume, due to its
superior spatial reliability related to the absence of
magnetic distortion. In all but one case the drawing
of the tumor and optic nerve could be easily done
using CT imaging alone. In one case (Patient V),
3-T MR added valuable inputs regarding the course
of the optic nerve in relation to the tumor. In all
cases, the optic nerve was identified (running
peripherally around the tumor in four cases and
being inglobated within the tumor in one case
[patient III]). In those 4 cases where the tumor
compressed and displaced the optic nerve, it was
possible to delineate and designate the optic nerve
as a critical structure during creation of the
treatment plan. The optic nerve in these 4 cases
remained outside the prescription isodose (70%),
being placed within the 50% isodose (patients I and
III), the 30% isodose (patient V) or the 20% isodose
(patient IV). As a direct consequence of the ability
of treatment planning to develop isodose distributions minimizing the optic nerve dose, the total dose
and dose/fraction to the optic nerve was kept to an
average of 11.2 Gy (range: 8 to 20 Gy) and 2.8 Gy
(range: 2 to 5 Gy). In the single case where the optic
nerve was encased within the tumor, no attempt was
made to draw it and the nerve received the same
dose as was given to the tumor. An effort was also
made to keep the dose to the retina, lens, and
portions of the optic nerve outside the tumor to a
minimum.
The treatment was administered using the
CyberKnifeÕ
Robotic
Radiosurgery
System
(Accuray, Inc., Sunnyvale, CA). Briefly, the
CyberKnife is characterized by a 6-MV linear
accelerator attached to a robotic manipulator, a
non-isocentric treatment planning system, and a
target localization mechanism based on real-time
X-ray imaging. During the treatment, digitally
reconstructed radiographs generated from the planning CT are automatically registered, using the
bony landmarks of the skull, with the orthogonal Xray images obtained frequently during sessions.
Based on the target position revealed by the imaging
system, the linear accelerator is moved to numerous
different positions within the room, emitting 100 to
200 highly collimated beams to reproduce the dose
264
P. Romanelli et al.
distribution specified in the treatment plan. An
average plan took approximately 25 min to deliver.
A custom-made plastic mask attached to the
treatment couch was used to provide mild restraint
during the treatment delivery.
Patients were administered 4 mg dexamethasone
at the end of each treatment session. Follow-up
included serial MR imaging (every 6 months for
2 years, then once a year) and assessment of visual
fields and acuity every 6 months. Imaging and
ophthalmological exams were performed and
assessed by independent radiologists and ophthalmologists and then reviewed at our institution.
Results
Vision outcomes are listed for each patient in
Table I. Median follow-up was 74 months (range:
36 to 88 months). Stable tumor size was detected on
serial imaging. A progressive improvement in both
visual fields and acuity was documented by an
independent ophthalmologist in all but one patient.
At the end of the first year post-treatment, a marked
visual improvement with near-total restoration of
visual fields and acuity was achieved in four of the
five patients, and this restoration remained stable
over the course of the follow-up period. One
patient, also affected by diabetic retinopathy,
showed a modest improvement after 6 months,
remaining stable thereafter. Two patients (I and V),
presenting with bilateral visual impairment due to
the distortion of the optic chiasm, experienced
bilateral visual improvement at 6-month follow-up,
attaining full recovery at 12 months. Proptosis
disappeared in one patient and remained stable in
the other. The patient with frank exophthalmos
harboring the largest meningioma (6.4 cm3) experienced a slight reversal of this condition accompanied by remission of the shunting of the optociliary
vessels one year post-treatment.
Discussion
We have shown that in a small cohort of patients
with ONSMs fractionated stereotactic radiosurgery
could produce excellent tumor control and, in most
cases, improvement in visual symptoms. Good
clinical outcomes combined with a very low rate of
complications would seem to be minimal requirements for the treatment of such lesions. In fact,
given the slow growth of these benign lesions, it is
worth asking whether they should be treated at all.
In 2002 Egan and Lessell published their observations on the natural progression of ONSM [17]
and reported that, with a 6.2-year follow-up,
approximately 50% of the untreated patients maintained stable visual acuity and three out of 16
patients actually showed a slight improvement over
time. These results prompted the researchers to
warn the neurosurgery community against treating
patients with ONSM with stable conditions and
thereby subjecting them to unnecessary risk. A
relatively large retrospective study published in 2002
[3] included 64 patients that were either simply
observed or treated with surgery only, with radiotherapy only, or with a combination of surgery and
radiotherapy. Although the very different patient
characteristics and treatment regimens made firm
conclusions somewhat difficult, the findings can be
summed up as not very promising for any of the
groups. The radiation-only group demonstrated the
fewest complications and the smallest degree of
deterioration of visual acuity. These patients
received 40 to 55 Gy conventional or conformal
radiotherapy, and at a mean 150.2-month follow-up
they experienced a 33.3% complication rate
(including retinopathy, iritis and temporal lobe
atrophy), but did not show a statistically significant
drop in acuity. Certainly, if surgical or radiationbased treatment is pursued, the potential benefit
should be measured against the risk of causing or
hastening blindness in relatively stable patients.
Aside from a few isolated case studies, the first
documented relatively conformal radiation treatment of ONSM was conducted by a group from the
University of California San Francisco in 1992 and
involved four patients treated with an immobilization device that aligned the optic nerve with a
vertical axis and used three small half-beams
blocked along this axis, thus shielding the optic
nerve [18]. The technique irradiated a relatively
small (58 cm3) volume with the dose to the 80%
isodose line. However, this group did not report on
the outcome of the treatment.
Pitz et al. [9] were the first to treat primary
ONSM with a fully fractionated course of stereotactically targeted radiation, an approach known as
fractionated stereotactic radiation therapy (FSRT).
They treated 15 patients with 54 Gy; at a mean
follow-up of 37 months (range: 12–71 months),
visual acuity had improved in one patient, visual
fields had improved in six patients, and the other
patients remained stable. No one experienced a
significant side effect. Secondary ONSM patients
faired slightly less well, according to a subsequent
report [19]: Six of 24 examined eyes showed
improvements in visual acuity, and seven of 26
examined eyes showed improvements in visual
fields; 17 and 19 eyes, respectively, maintained
stability in visual acuity and visual field.
Staged image guided robotic radiosurgery for optic nerve sheath meningiomas
In the following year, Narayan et al. from the
University of Michigan treated 14 patients using the
technique of three-dimensional conformal radiotherapy (3D-CRT) and obtained similar results to
those obtained using FSRT [20]. Five patients had
improvement in visual acuity, two worsened, and
the rest remained stable over a median of 51.3
months. Nine patients showed improved visual
fields. Baumert et al. from Switzerland treated 23
patients with tumor progression using FSRT with
50.4 Gy delivered over six weeks [21]. With a
median follow-up of 20 months, 16 of their patients
experienced improvement in vision, five had stable
vision, and one got worse. Ninety-five percent of
patients achieved stable disease.
More recent studies of FSRT have continued to
demonstrate its potential for controlling the growth
of ONSMs while stabilizing or reversing visual
deficits caused by them. Milker-Zabel et al. [22]
treated 15 patients with FSRT as primary treatment
(other patients were treated after biopsy or surgery
or for recurrences) to a median a median total dose
of 54.9 Gy. At a median follow-up of 4.5 years,
local tumor control was 100% and 97% of patients
showed stable or improved visual acuity. Arvold
et al. [23] treated 25 patients with FSRT using
photons or protons to a median dose of 50.4 Gy
equivalents. At a median follow-up of 30 months,
95% of patients had improved (14 patients) or stable
(7 patients) visual acuity, and 95% showed no
progression on imaging. A single recurrence was
noted 11 years after treatment. Comparable outcomes were reported by Lesser et al. [24]. Thus,
FSRT may be gaining acceptance as a low-risk
approach to controlling ONSM growth and symptom progression. In fact, Smee et al. [25] reserved
stereotactic radiosurgery (see below) for patients
whose vision was not likely to be affected by
treatment; when preservation or improvement of
vision was a therapeutic goal they opted for FSRT.
They ultimately obtained 100% tumor control and
vision preservation in all but one patient using their
methods.
Single-session SRS treatment of ONSMs has also
been reported [26]. Sitathanee et al. [27] treated a
patient who had already lost vision with a single
15-Gy dose. There were no complications to the
contralateral eye.
Three patients were treated with single-session
SRS in the report by Smee et al. [25]. As noted
above, they recommended SRS only when preservation of vision was not a goal of treatment. Liu et al.
[28] reported on outcomes of Gamma Knife SRS to
a mean dose of 13.3 Gy for 30 patients. In nine
patients who still had vision and whose ONSMs
surrounded the optic nerve, SRS was delivered in
265
two sessions. At a median follow-up of 56 months
the tumor control rate was 93.3%. Vision deteriorated in 20% of patients; it was not indicated if these
patients were treated in a single fraction or in two
fractions.
Staged radiosurgery outcome for the treatment of
ONSM was preliminarily reported by our group in
2007 [16]. The current paper provides a larger
series with prolonged follow-up. Staged radiosurgery was performed with the aim of stopping disease
progression and maintaining visual function.
Restoration to normal vision in 4 out of 5 patients
within 6 to 12 months following treatment was an
unexpected gift, most likely related to improved
vascular supply to the involved optic nerve following
tumor irradiation. The ability to use very tight dose
distributions combined with hypofractionation was
perhaps associated with the highest degree of
protection of the optic nerve that technology has
yet made available. In two cases (where a
CyberKnife G3 model was used) the optic nerve
was included in the 50% isodose, while in the other
two cases (using a CyberKnife G4) it was kept
outside the 30% isodose. In the first two cases the
optic nerve received approximately 2.5 Gy per
fraction (for a total dose of 10 Gy in 4 fractions),
while in the latter two cases the optic nerve dose per
fraction was less than 1.5 Gy (total dose 6 Gy). The
tumor received 5 Gy per fraction (total dose 20 Gy).
The patient whose optic nerve was enveloped by the
ONSM could not be spared from receiving a similar
dose to the nerve and tumor. Nevertheless, this
patient showed substantial improvement in visual
fields and acuity and maintained this improvement
over time (the first patient of this series having had a
follow-up of longer than 7 years). This small clinical
series demonstrates a promising non-invasive
approach to treating ONSM. Patients can be treated
in less than a week as opposed to the full month
required by conventional radiation techniques,
including SFRT. The degree of sparing of the
optic nerve when this is peripherally displaced by the
tumor is unmatched: robotic image guided radiosurgery can provide doses effective at halting the
tumor progression and restoring visual function,
while at the same time the dose received by the optic
nerve itself can be less than 1.5 Gy per fraction (as
described for the last two cases treated using a
Cyberknife G4).
Conclusions
Robotic image guided radiosurgery proved to be
safe and effective in a small series of patients
harboring ONSM. These preliminary results pave
266
P. Romanelli et al.
the way for a prospective multicentric study aimed
at investigating the safety and efficacy of staged
CyberKnife radiosurgery as a primary treatment
option for ONSM.
Declaration of interest:
conflicts of interest
The authors report no
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