non-isocentric radiosurgical rhizotomy for trigeminal neuralgia
DESCRIPTION
Clinical outcome study involving patients with trigeminal neuralgia treated with CyberKnife radiosurgeryTRANSCRIPT
Non-isocentric Radiosurgical Rhizotomy for Trigeminal Neuralgia
John R. Adler, Jr, Regina Bower, Guarav Gupta, Michael Lim, Allen Efron, Iris C.
Gibbs, Steve D. Chang and Scott G. Soltys
Corresponding author:
John R. Adler, Jr, MD
Department of Neurosurgery
Stanford University Medical Center
300 Pasteur Drive
Stanford, CA 94305
PH: 650 723-5573
FAX: 650 725-1784
EMAIL: [email protected]
Running Title: CyberKnife Rhizotomy for Trigeminal Neuralgia
Keywords: Trigeminal Neuraglia, Radiosurgery, Rhizotomy, Non-isocentric,
CyberKnife
1
Abstract
Objective: Although stereotactic radiosurgery is an established procedure for
treating trigeminal neuralgia (TN), the likelihood of a prompt and durable
complete response is not optimal. Moreover, the incidence of facial numbness
remains a challenge. To address these limitations, a new more anatomic
radiosurgical procedure was developed that utilizes the CyberKnife to lesion an
elongated segment of the retrogasserian cisternal portion of the trigeminal
sensory root. Because the initial experience with this approach resulted in an
unacceptably high incidence of facial numbness, a gradual dose and volume de-
escalation was performed over several years. In this single-institution
prospective study, we evaluated clinical outcomes in a group of trigeminal
neuralgia patients who were lesioned with seemingly optimized non-isocentric
radiosurgical parameters.
Methods: Forty-six patients with intractable idiopathic TN were treated between
January 2005 and June 2007. Eligible patients were either poor surgical
candidates or had failed prior microvascular decompression (MVD) or destructive
procedures. During a single radiosurgical session a 6-mm segment of the
affected nerve was treated with a mean marginal prescription dose of 58.3 Gy
and mean maximal dose (Dmax) of 73.5 Gy. Monthly neurosurgical follow-up
was performed until the patient became pain-free. Longer term follow-up was
done both in the clinic and over the phone. Outcomes were graded as excellent
(pain-free and off medication), good (>90% improvement while still on
medication), fair (50-90% improvement) or poor (no change or worse). Facial
numbness was assessed using the Barrow Neurological Institute (BNI) Facial
Numbness score.
Results: Symptoms disappeared completely in 39 (85%) patients after a mean
latency of 5.2 weeks. In most of these patients pain relief began within the first
2
week. TN recurred in a single patient after a pain-free interval of 7 months; all
symptoms abated after a second radiosurgical procedure. Three additional
patients underwent a repeat rhizotomy after failing to respond adequately to the
first operation. After a mean follow-up of 12.4 months, patient-reported
outcomes were excellent in 33 (72%), good in 11 (24%) and poor/no
improvement in 2 (4%) cases. Significant ipsilateral facial numbness (BNI III)
was reported in ten (22%) cases.
Conclusions: Optimized non-isocentric CyberKnife parameters for TN treatment
resulted in high rates of pain relief and a more acceptable incidence of facial
numbness than reported previously. Longer follow-up will be required to
establish whether the durability of symptom relief after lesioning an elongated
segment of the trigeminal root is superior to isocentric radiosurgical rhizotomy.
3
Introduction
The treatment of trigeminal neuralgia (TN) by radiosurgical rhizotomy was
conceived by Lars Leksell (9). Over the past several decades radiosurgical
parameters for treating this condition have been optimized, especially for the
Gamma Knife. By investigating a range of maximal doses (Dmax from 60 to 90
Gy)(2, 8, 16) and a variety of lesion locations along the retrogasserian trigeminal
root (from the root entry zone to just proximal to the semilunar ganglion)(3, 5, 8,
12, 15, 16, 21) neurosurgeons are now able to maximize the likelihood of pain
relief while minimizing the risk of facial dysesthesias or numbness. Recent
outcome studies report that complete long-term pain relief can be achieved in
66% to 84% of patients undergoing radiosurgical rhizotomy alone, while varying
degrees of facial numbness are observed in 10% to 54% of cases (13, 14, 16,
18). As a general rule, better pain relief appears to correlate with higher rates of
sensory loss (16, 19, 20).
Given the straightforward objective of radiosurgical rhizotomy in patients with TN,
it is unclear why outcomes vary so much between patients. The long latency to
pain relief and its poor durability in some patients are lingering shortcomings of
the procedure. In contrast, immediate, long-lasting symptom relief is routinely
achieved in similar patients who undergo less expensive percutaneous
radiofrequency (RF) rhizotomy (22). Perhaps with these limitations in mind,
some neurosurgeons have sought to improve the outcome after radiosurgery by
increasing the length of the irradiated nerve (1, 6, 11). However, this concept
was discredited in a small randomized study by Flickinger and colleagues (6). In
a multi-institutional study that utilized the Gamma Knife, two adjacent 4-mm
shots served to lengthen the segment of lesioned trigeminal nerve. Because of a
trend towards increased “complications” in the experimental group (albeit not
statistically significant), the study was stopped short of complete patient accrual;
the investigators concluded “Increasing the treatment volume to include a longer
4
nerve length for trigeminal neuralgia radiosurgery does not significantly improve
pain relief but may increase complications”. Although Flickinger et al. did not
provide much qualitative detail, facial numbness and dysesthesias were central
to the early termination of this study. The outcomes of this study are surprising
because they violate the direct relation between target dose, target volume, and
clinical response that underlies much of radiosurgery. One would have
anticipated that any increase in facial numbness would have been accompanied
by an improved rate and durability of pain relief. It seems possible that chance
may have contributed to the paradoxical findings observed in the small Flickinger
et al series.
With the goal of enhancing the clinical response to radiosurgery, the first author
began in 2002 to lesion a longer segment of the trigeminal sensory root using a
relatively homogeneous radiation dose. Because of the CyberKnife’s capacity
for non-isocentric irradiation, it is a straightforward process to conformally lesion
an elongated non-spherical target with greater dose uniformity, as opposed to
instruments that treat only iso-centrically. In the initial report detailing the results
of 41 patients treated in this manner, 92.7% of patients experienced initial pain
relief after only a median of 7 days post radiosurgery; pain relief was maintained
in 78% of patients at 11 months. However, facial numbness developed in 73% of
patients (11). To address this shortcoming, dose and volume were gradually de-
escalated. Since January 2005, appropriately selected TN patients at Stanford
have been managed with a relatively consistent radiosurgical lesion. In this
study we analyze the outcomes in this cohort of patients and compare it to
published radiosurgery series.
Materials and Methods
Patients
Patient data was reviewed under an IRB-approved protocol. All cases had
idiopathic TN of several years duration; pain symptoms were either refractory to
5
standard anti-convulsants or the patient suffered from severe drug-induced side
effects. Cases involving either multiple sclerosis or tumors were excluded from
this analysis as was any patient with atypical facial pain. A total of 46
consecutive TN patients who met these criteria were lesioned at Stanford
University Medical Center by CyberKnife rhizotomy between January 2005 and
June of 2007 (see Table 1). In this group were 17 males and 29 females with a
median age of 78 years (range 40-94 years). The average time from the earliest
onset of TN symptoms to stereotactic radiosurgery was 8.6 years (range 8
months to 20 years). Eleven patients (24%) had failed prior surgical procedures
(averaging 1.8 procedures per patient) directed towards their trigeminal
symptoms, which included microvascular decompression (MVD) (14 cases) and
rhizotomy by means of an open (3), glycerol (5) or gamma knife (3) technique.
Eleven patients (24%) reported either a moderate or significant degree of facial
numbness prior to CyberKnife rhizotomy, which unfortunately was not
prospectively scored on the BNI scale.
TABLE 1: Patient Characteristics (N=46)
Male/Female 17/29
Age (median, range) 78 years, (40-94 years)
Time from TN onset to radiosurgery (mean, range) 8.6 years (8-20 years)
Right side/Left side 29/17
Prior surgical procedures (24% of patients total)
Microvascular decompression 14 cases
Open rhizotomy 3 cases
Glycerol rhizotomy 5 cases
Gamma Knife 3 cases
Pre-CyberKnife facial numbness 11 patients (26%)
Radiosurgical Procedure
Radiosurgical trigeminal rhizotomy was performed with the CyberKnife
Radiosurgical System (Accuray Inc., Sunnyvale, CA) utilizing the technique
6
reported previously (11). Both the 400 monitor units (MU)/min CyberKnife G3
and 600 MU/min CyberKnife G4 models were used over the course of this study.
To summarize, a customized Aquaplast mask (Medtech, Des Moines, Iowa) was
fashioned for each patient. While immobilized in the mask, the entire head was
imaged with thin section (1.25 mm slice thickness) contrast computerized
tomography (CT); the first 15 cases in this series underwent a lumbar intrathecal
injection of iodinated contrast (8 cc of Iohexal) prior to CT. Patients were then
imaged with a fast imaging employing steady-state acquisition (FIESTA)
sequence magnetic resonance (MR) imaging using 3D volumetric acquisition and
1 mm slice thickness. These CT and MR techniques reliably demonstrated the
trigeminal nerve in negative relief as it transited the pre-pontine cistern (4).
Midway through the current series we documented the reliability and spatial
fidelity of radiosurgical targeting performed only with T2-weighted MR scanning.
(4) Once confident in the accuracy of MRI-based targeting, the use of CT
cisternography for this purpose was largely abandoned.
On the CyberKnife treatment planning workstation, the MRI and CT scans were
fused. Standard segmentation tools were used to delineate on the fused data
sets a 6-mm length of the retrogasserian trigeminal sensory root as defined in the
reconstructed sagittal plane of the nerve. This target volume deliberately spared
the proximal 2 to 3 mm of trigeminal dorsal root at the brainstem. Dose to the
brainstem and semilunar ganglia was restricted to the maximal extent possible.
The earlier patients in the current investigation were treated with the 65 cm
source to axis distance (SAD) “trigeminal node set” which provides a nominal
collimator diameter at isocenter of 6 mm. After the higher-output CyberKnife G4
model was installed at Stanford, patients were treated using a 5-mm collimator
and an 80 cm SAD. A mean marginal prescription dose of 58.3 Gy (range 56-62
Gy) and Dmax of 73.5 Gy (range 71.4-86.2 Gy) were used over the course of this
series. The average prescription isodose line was 79%. Figure 1 depicts a
representative radiosurgical plan for trigeminal neuralgia. Note the relatively
7
homogeneous dose within the target volume that is achievable with a non-
isocentric technique.
Radiosurgery was performed as an outpatient procedure. Treatment sessions
lasted approximately one hour. At the end of the procedure patients were given 4
mg of dexamethasone.
Follow-up
Patients were followed at one-month intervals until they were pain-free, at which
point anticonvulsants were tapered. Subsequent follow-up occurred at monthly
intervals to insure a stable clinical status. Any relapse of pain or the
development of facial numbness was clinically re-evaluated in person. At each
point of contact, patients were grouped into one of four categories; 1) excellent
(pain-free and off medication), good (>90% improvement while still on
medication), fair (50-90% improvement) or poor (no change or worsening pain).
The presence and timing of facial numbness was also recorded and classified by
BNI Facial Numbness Score (see Table 2) (19). Five patients (11%) underwent
repeat CyberKnife rhizotomy more than 6 months after the initial procedure; in
four of these cases there was inadequate clinical response to the first
radiosurgical procedure while in one patient there was a relapse in TN symptoms
seven months after the initial operation. Longer term follow-up was done by mail
and telephone. Follow-up data was maintained in a prospective database
approved by the Stanford IRB.
Results
Thirty-nine patients (85%) in this study had complete disappearance of their
trigeminal neuralgia and were off medications at some point over the course of
follow-up. At a mean follow-up of 12.4 months (range 6-29 months), 34
(72%) patients graded their pain relief as excellent and 11 (24%)
described it as good. Consequently, 96% of patients obtained
8
meaningful relief of TN symptoms after CyberKnife rhizotomy. Within
this group were 5 patients who at 6 months continued to have severe
TN and were retreated; the eventual outcome for these five salvage
cases was generally excellent (2) or good (2). However, one of the 5
retreated patients had a poor outcome. Although across the entire series
an improvement in symptoms was typically experienced within a few days or
weeks of radiosurgery, the full benefits were obtained after a mean latency of 5.2
weeks (ranging from immediately to 6 months after the procedure).
Trigeminal neuralgia recurred in only a single patient, 7 months post
radiosurgery; repeat CyberKnife radiosurgical rhizotomy subsequently rendered
this patient pain-free. At last follow-up, 11 patients (24%) reported a significant
improvement (3 cases) or even complete abatement (8 cases) in TN symptoms
but required, or elected to continue, anticonvulsants for controlling their pain;
three patients refused to give up their medication due only to concern that their
pain might return. Meanwhile, after rhizotomy TN symptoms were deemed to be
worse in only one case.
Among the 41 patients who had only a single radiosurgical rhizotomy,
significant new ipsilateral facial numbness was reported in 7 cases (17%).
New onset sensory loss typically involved the hemicranium and occurred on
average 7 months after the procedure. Interestingly, only one of five patients
who underwent repeat radiosurgery (after a prior Gamma Knife or
CyberKnife rhizotomy) developed significant subsequent facial
numbness. At the time of most recent follow-up, facial sensation and
dyesthesia were categorized in all patients according to BNI score as
follows: BNI I: 28, BNI II: 11 and BNI III: 7 (Table 2). It is important to
note that eleven patients had some measure of numbness prior to
CyberKnife rhizotomy and at last follow-up there were no cases of
anaesthesia dolorosa.
9
Table 2 – Barrow Neurological Institute Facial Numbness Score and outcomes
Grade Description No. Patients (Total=46)
I No facial numbness 28
II Mild facial numbness, not bothersome 11
III Facial numbness, somewhat bothersome 7
IV Facial numbness, very bothersome 0
Twenty-eight patients (61%) reported the optimal result of being pain-
free and off anti-convulsants, while retaining pretreatment facial
sensation. Six additional patients were pain-free but elected to either
remain on reduced doses of anti-convulsants or were unable to taper
off such drugs completely without experiencing some recurrent
symptoms. Consequently, CyberKnife rhizotomy resulted in 74% of all
cases experiencing good to excellent pain relief without significant
facial numbness; if one includes 9 additional patients who developed
significant facial numbness, then 96% of all patients experienced complete or
near complete relief of trigeminal neuralgia. It is especially noteworthy that
among the 31 TN patients who had never undergone any prior surgical
procedure, 100% had either a good or excellent response to
CyberKnife rhizotomy.
Discussion
The benefits of radiosurgical rhizotomy for TN using the standard isocentric
technique are, for many patients, insufficient. Because of the latency of pain
relief, overall rate of response, and recurrence of TN symptoms, radiosurgical
rhizotomy has limited appeal in the eyes of some neurosurgeons. In an attempt
to address the shortcomings of the standard isocentric technique, our group has
sought to refine over several years a procedure that utilizes non-isocentric
radiosurgery to lesion an elongated segment of the retrogasserian portion of the
10
trigeminal sensory root. Over time treatment parameters have been optimized to
enhance the pain response and reduce facial numbness. The primary objective
of the current prospective single-institution study was to characterize short-term
outcomes with this technique.
The overall response rate observed in the current CyberKnife series appears
satisfactory. In fact 100% of the patients that had not previously undergone a
surgical procedure reported their outcome as either good (13%) or excellent
(87%); one of these patients needed to be treated twice to achieve this outcome.
It is reasonable to propose that this high rate of response is attributable, at least
in part, to the longer length of trigeminal nerve lesioned with the CyberKnife.
Although the methods used to score the response of TN to trigeminal rhizotomy
are relatively consistent among most clinical series, patient inclusion criteria,
length of follow-up and measures of facial numbness and/or dysesthesia vary
widely. Consequently it is difficult to directly compare those outcomes with the
current study, and as a result, it cannot be determined at present whether or not
irradiating a longer nerve segment is clinically beneficial. Nevertheless, crude
comparisons with published radiosurgical rhizotomy series that have utilized
isocentric Gamma Knife (16, 18) and Linac-based (21) procedures, suggest that
the outcome with non-isocentric radiosurgical rhizotomy is at least competitive in
terms of overall rate of response. Ideally, the current experience could provide a
reasonable substrate for a randomized trial which compared the two procedures.
The rate of numbness observed in the present series appears to be greater than
first reported by several groups using an isocentric Gamma Knife technique (12,
17, 19). However, higher rates of facial numbness after Gamma Knife rhizotomy
have also been reported, especially with larger and more effective dosing
regimens (14, 16). Consequently, the overall incidence and characteristics of
sensory loss experienced by some of the patients in the current CyberKnife study
seem comparable to what has been reported previously with more conventional
isocentric procedures.
11
While there are important technical differences, the relatively unremarkable
incidence of facial sensory changes we observed in the present series may
challenge one of the key findings reported in Flickinger et al. (6). This
randomized trial, which examined the utility of two adjacent 4-mm Gamma Knife
shots when lesioning the trigeminal nerve, needed to be terminated prematurely
when patients in the experimental arm developed severe dysesthesias. The
investigators concluded that a longer radiosurgical lesion merely increased the
likelihood of “complications” without altering the pain response. What remains
unclear is why Flickinger et al. did not encounter an increased rate of response
among patients treated with a longer lesion of the trigeminal sensory root. The
failure to find such a response would appear to run counter to the experience
described by our group (10, 23) and perhaps the reports of other Gamma Knife
series that found a direct correlation between integral dose to the trigeminal
nerve and the likelihood of pain relief (16). Moreover the Flickinger et al. findings
would seem to be at odds with the widely observed dose-volume-response
phenomenon seen throughout most of radiosurgery. Of note, the Flickinger et al.
study compared the standard one-isocenter treatment to a solitary experimental
group in which the longer rhizotomy consisted of 2 adjacent isocenters. By
comparison, our group required several years to slowly titrate a radiosurgical
dose and volume for lesioning the trigeminal nerve which is proving in our
experience to be more optimal in terms of pain relief and avoidance of facial
numbness. Perhaps a wider investigation of volumes and doses delivered with a
2-isocenter Gamma Knife technique might reveal a combination that improves
pain relief without further risk of unpleasant facial numbness. Only further study,
and most probably a randomized trial, can determine whether or not a longer
trigeminal rhizotomy ultimately has any clinical advantages.
One of the primary rationales for modifying the standard radiosurgical rhizotomy
technique was to increase the durability of pain relief. Because only one patient
(1/39) suffered relapse in their trigeminal neuralgia (7 months post SRS), the
12
current experience is encouraging. Nevertheless, much longer follow-up will be
required to prove that lesioning a longer segment of nerve can significantly
increase the durability of the radiosurgical rhizotomy.
The incidence and intensity of delayed numbness observed in the current series
represents a substantial improvement over what was previously reported for
CyberKnife rhizotomy (11, 23), and, importantly, there were no instances of
anesthesia dolorosa. As a consequence, it appears that the dose-volume
parameters being used with the present non-isocentric technique make for a
better clinical outcome. Given the reported latency between radiosurgery and
the onset facial numbness, it is quite possible that with further follow-up
additional patients will develop sensory symptoms. However, because in the
present study the mean overall follow-up is 12.6 months, while the mean time to
occurrence of numbness of 7 months, it seems unlikely that loss of facial
sensation will occur in enough additional patients to alter this primary finding.
Ultimately, it seems clear that numbness is significantly less likely using the
optimized treatment parameters of the present study than it was during the
development stages of CyberKnife rhizotomy for TN.
It is worth pointing out that TN is somewhat unique among pain syndromes in
that pain is usually either present or absent. As a consequence the large
majority of patients with complete relief were easy to categorize as such. In
contrast the nature of symptoms and outcome among patients with only partial
pain relief was more complex and less conducive to the relatively simplistic
measuring tools used in this investigation. Moreover several of the patients in
this series had co-existing facial pain syndromes that were not trigeminal
neuralgia-like and were precipitated in part by previous failed ablative procedures
or microvascular decompression. Because some of these same patients also
eventually developed post-rhizotomy delayed facial numbness, it was often
difficult to distinguish new sensory symptoms from their pre-existing pain
condition. Therefore, one of the limitations of the current investigation is that
13
unlike the recent Regis et al study there is not a more detailed analysis of our
patients' ultimate facial sensation. (18). Despite this shortcoming, the current
investigation should provide a useful starting point for future investigation.
The biologic mechanism underlying the cessation of TN symptoms after
radiosurgical rhizotomy remains poorly defined. Some investigators have
concluded that the likelihood of a clinical response to radiosurgery correlates with
the development of facial numbness (16, 19). This suggests that a common
mechanism underlies these two phenomena. However, their very different time
course implies distinct mechanisms underlie pain relief and facial numbness; TN
pain abates relatively rapidly after a radiosurgical rhizotomy, while facial
numbness is clearly a delayed event (6-9 months or more post-radiosurgery).
Meanwhile, both the latency of sensory changes and the appearance of
enhancement on contrast MR at the root entry zone (REZ), the later being
consistent with breakdown in the blood-brain barrier, strongly suggest that facial
numbness stems from injury to the microvasculature of the trigeminal nerve and
adjacent brainstem (7). If so, such a phenomenon raises some intriguing
possibilities for intervention. In particular, the use of an intravascular free radical
scavenger, like Ethyol, at the time of radiosurgery might provide relative
radioprotection to endothelium and limit the incidence of delayed microvascular
injury. Theoretically, such an agent would not alter the biologic mechanism
underlying the therapeutic benefits of radiosurgery. A randomized trial is being
planned to investigate such a possibility.
Conclusion
Compared to previous reports that describe the clinical outcome after non-
isocentric radiosurgical rhizotomy in patients with trigeminal neuralgia, the
present investigation demonstrates both high rates of pain relief and an
acceptable incidence of facial numbness. We are not able to determine whether
this technique can ultimately improve upon either the rate of response or
14
durability of symptom relief that can be achieved with the standard isocentric
radiosurgical rhizotomy. Further study is warranted, and ideally a randomized
trial comparing isocentric and non-isocentric techniques.
Disclosure
John R. Adler is a shareholder and a member of the board of directors of
Accuray, Inc., the manufacturer of the CyberKnife Radiosurgical System. The
other authors have no personal financial interest in Accuray, Inc or the
CyberKnife System and have received no financial support in conjunction with
the generation of this article.
Acknowledgement
The authors would like to acknowledge the helpful suggestions and diligent edits
made by David Schaal PhD during the preparation of this manuscript.
15
REFERENCES
1. Alpert TE, Chung CT, Mitchell LT, Hodge CJ, Montgomery CT, Bogart JA,
Kim DY, Bassano DA, Hahn SS: Gamma knife surgery for trigeminal
neuralgia: improved initial response with two isocenters and increasing
dose. J Neurosurg 102 Suppl:185-188, 2005.
2. Brisman R: Gamma knife surgery with a dose of 75 to 76.8 Gray for
trigeminal neuralgia. J Neurosurg 100:848-854, 2004.
3. Brisman R, Mooij R: Gamma knife radiosurgery for trigeminal neuralgia:
dose-volume histograms of the brainstem and trigeminal nerve. J
Neurosurg 93 Suppl 3:155-158, 2000.
4. Chavez GD, De Salles AA, Solberg TD, Pedroso A, Espinoza D,
Villablanca P: Three-dimensional fast imaging employing steady-state
acquisition magnetic resonance imaging for stereotactic radiosurgery of
trigeminal neuralgia. Neurosurgery 56:E628; discussion E628, 2005.
5. Cheuk AV, Chin LS, Petit JH, Herman JM, Fang HB, Regine WF: Gamma
knife surgery for trigeminal neuralgia: outcome, imaging, and brainstem
correlates. Int J Radiat Oncol Biol Phys 60:537-541, 2004.
6. Flickinger JC, Pollock BE, Kondziolka D, Phuong LK, Foote RL, Stafford
SL, Lunsford LD: Does increased nerve length within the treatment
volume improve trigeminal neuralgia radiosurgery? A prospective double-
blind, randomized study. Int J Radiat Oncol Biol Phys 51:449-454, 2001.
7. Gorgulho AA, De Salles AA: Impact of radiosurgery on the surgical
treatment of trigeminal neuralgia. Surg Neurol 66:350-356, 2006.
16
8. Kondziolka D, Lunsford LD, Flickinger JC, Young RF, Vermeulen S, Duma
CM, Jacques DB, Rand RW, Regis J, Peragut JC, Manera L, Epstein MH,
Lindquist C: Stereotactic radiosurgery for trigeminal neuralgia: a
multiinstitutional study using the gamma unit. J Neurosurg 84:940-945,
1996.
9. Leksell L: Sterotaxic radiosurgery in trigeminal neuralgia. Acta Chir
Scand 137:311-314, 1971.
10. Lim M, Cotrutz C, Romanelli P, Schaal D, Gibbs I, Chang SD, Adler JR:
Stereotactic radiosurgery using CT cisternography and non-isocentric
planning for the treatment of trigeminal neuralgia. Comput Aided Surg
11:11-20, 2006.
11. Lim M, Villavicencio AT, Burneikiene S, Chang SD, Romanelli P, McNeely
L, McIntyre M, Thramann JJ, Adler JR: CyberKnife radiosurgery for
idiopathic trigeminal neuralgia. Neurosurg Focus 18:E9, 2005.
12. Maesawa S, Salame C, Flickinger JC, Pirris S, Kondziolka D, Lunsford
LD: Clinical outcomes after stereotactic radiosurgery for idiopathic
trigeminal neuralgia. J Neurosurg 94:14-20, 2001.
13. Massager N, Lorenzoni J, Devriendt D, Levivier M: Radiosurgery for
trigeminal neuralgia. Prog Neurol Surg 20:235-243, 2007.
14. Massager N, Murata N, Tamura M, Devriendt D, Levivier M, Regis J:
Influence of nerve radiation dose in the incidence of trigeminal dysfunction
after trigeminal neuralgia radiosurgery. Neurosurgery 60:681-687;
discussion 687-688, 2007.
17
15. Nicol B, Regine WF, Courtney C, Meigooni A, Sanders M, Young B:
Gamma knife radiosurgery using 90 Gy for trigeminal neuralgia. J
Neurosurg 93 Suppl 3:152-154, 2000.
16. Pollock BE, Phuong LK, Foote RL, Stafford SL, Gorman DA: High-dose
trigeminal neuralgia radiosurgery associated with increased risk of
trigeminal nerve dysfunction. Neurosurgery 49:58-62; discussion 62-54,
2001.
17. Regis J, Metellus P, Dufour H, Roche PH, Muracciole X, Pellet W, Grisoli
F, Peragut JC: Long-term outcome after gamma knife surgery for
secondary trigeminal neuralgia. J Neurosurg 95:199-205, 2001.
18. Regis J, Metellus P, Hayashi M, Roussel P, Donnet A, Bille-Turc F:
Prospective controlled trial of gamma knife surgery for essential trigeminal
neuralgia. J Neurosurg 104:913-924, 2006.
19. Rogers CL, Shetter AG, Fiedler JA, Smith KA, Han PP, Speiser BL:
Gamma knife radiosurgery for trigeminal neuralgia: the initial experience
of The Barrow Neurological Institute. Int J Radiat Oncol Biol Phys
47:1013-1019, 2000.
20. Shetter AG, Rogers CL, Ponce F, Fiedler JA, Smith K, Speiser BL:
Gamma knife radiosurgery for recurrent trigeminal neuralgia. J Neurosurg
97:536-538, 2002.
21. Smith ZA, De Salles AA, Frighetto L, Goss B, Lee SP, Selch M, Wallace
RE, Cabatan-Awang C, Solberg T: Dedicated linear accelerator
18
radiosurgery for the treatment of trigeminal neuralgia. J Neurosurg
99:511-516, 2003.
22. Taha JM, Tew JM, Jr., Buncher CR: A prospective 15-year follow up of
154 consecutive patients with trigeminal neuralgia treated by
percutaneous stereotactic radiofrequency thermal rhizotomy. J
Neurosurg 83:989-993, 1995.
23. Villavicencio AT, Lim M, Burneikiene S, Romanelli P, Adler JR, McNeely
L, Chang SD, Fariselli L, McIntyre M, Bower R, Broggi G, Thramann JJ:
CyberKnife radiosurgery for trigeminal neuralgia treatment: A preliminary
multicenter experience. Neurosurgery, 2008 in press.
19
Figure 1
Legend
This screen shot taken from the CyberKnife treatment planning workstation, depicts a representative radiosurgical plan for trigeminal neuralgia. Note the relatively homogeneous dose within the target volume that is achievable with a non-isocentric technique.
20