Case Report Received: March 22, 2011 Accepted after revision: July 18, 2011 Published online: September 13, 2011
Pediatr Neurosurg DOI: 10.1159/000330886
Initial Experience with the Use of Remote Control Monitoring and General Anesthesia during Radiosurgery for Pediatric Patients Kotoe Kamata a Motohiro Hayashi b, c Osamu Nagata a, d Yoshihiro Muragaki b, c Hiroshi Iseki b, c Yoshikazu Okada b Makoto Ozaki a a
Department of Anesthesiology, Tokyo Women’s Medical University, b Department of Neurosurgery, Neurological Institute, Tokyo Women’s Medical University, and c Faculty of Advanced Techno-Surgery, Institute of Advanced Biomedical Engineering and Science, Tokyo Women’s Medical University, Tokyo, and d Department of Anesthesiology, Saitama Medical Center, Jichi Medical University, Saitama, Japan
Key Words Pediatric radiotherapy ⴢ Gamma Knife radiosurgery ⴢ Automated setting ⴢ Anesthesia outside the operating room ⴢ Pediatric anesthesia
Abstract The demand for general anesthesia in pediatric radiosurgery has been increasing, but the issues involved are not highlighted well in the medical literature. We developed remotely controlled monitoring and anesthesia techniques, and applied our system to three pediatric patients who underwent Gamma Knife radiosurgery with automated settings. Based on the perioperative safety management, the following issues are of considerable concern: to avoid emotional trauma associated with the treatment, to secure airway patency in a variety of head positions, and to apply all standard monitors. In this report, we describe the details of our project with a comprehensive literature review. Copyright © 2011 S. Karger AG, Basel
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Introduction
Safe and effective general anesthesia for pediatric radiosurgical patients, especially for those receiving Gamma Knife radiosurgery (GKRS), has been challenging [1– 2]. Although the new robotic technology (automatic positioning system: APS) of Gamma Knife has successfully improved patient and medical team comfort [3], stereotactic radiosurgical procedures usually require a longer amount of time for a single treatment setting than other radiation therapies. In addition, GKRS requires multimodal imaging techniques including computed tomography (CT), angiography and magnetic resonance imaging (MRI) prior to irradiation therapy with multiple transfers of the patient. It has been reported that the procedure duration is one of the significant risk factors for pediatric radiation therapy performed under general anesthesia, even though anesthesia-related complications are rare [4]. With the technological advances of GKRS, a fully automated model, Leksell Gamma Knife Perfexion (Elekta Instruments AB, Stockholm, Sweden), was introduced recently. This latest model has the benefit of saving total treatment time due to a completely robotized system: 98.99% of the cases could be performed with a single run [5]. However, the automated settings could be disadvantaKotoe Kamata, MD, PhD Department of Anesthesiology, Tokyo Women’s Medical University 8-1 Kawada-cho, Shinjuku-ku Tokyo 162-8666 (Japan) Tel. +81 3 5269 7336, E-Mail macaroon @ nifty.com
Table 1. Characteristics of the patients Demographics
Operative backgrounds
Operative data
age gender height weight ASA(years) (M/F) (cm) (kg) PS
diagnosis
complications
CT scana MRI scanb angiographyc GKRSd anesthesiae emergencef (min) (min) (min) (min) (min) (min)
Case 1
10
M
127
27
1
emotional trauma mental retardation
25
50
not required 310
480
17
Case 2
3
F
86
10
2
mental retardation
35
80
not required 180
390
15
Case 3
4
M
100
20
1
recurrent craniopharyngioma recurrent medulloblastoma AVM
emotional trauma
45
35
100
575
7
295
ASA-PS = American Society of Anesthesiologists Physical Status Classification System; AVM = arteriovenous malformation. a Time from entry to and discharge from CT unit. b Time from entry to and discharge from MRI suite. c Time from entry to and discharge from angiography room. d Time from entry to and discharge from Gamma Knife unit. e Time from anesthetic induction to extubation. f Time from termination of propofol infusion to appearance of any clinical signs of emergence.
geous especially for pediatric patients who require general anesthesia and need to be examined directly in respect to their condition. Thus we need to take special considerations in the areas of anesthesia and monitoring for patients who receive GKRS with the automated settings. The goals of intraoperative management for pediatric radiotherapy include: (1) avoidance of emotional trauma associated with the treatment; (2) patient immobilization during irradiation; (3) airway management in a variety of head positions; (4) rapid onset of and recovery from general anesthesia; (5) reduction of unnecessary exposure to irradiation by medical staff. In this article, we will report our initial experience of general anesthesia with continuous monitoring by using several kinds of remote control techniques and existing hospital facilities in order to establish a remote control patient management system. We applied this system to three pediatric patients who received GKRS at our institute in order to investigate its safety and utility.
Case Report Case Presentation All patients were classified as class 1 or 2 according to the American Society of Anesthesiologists Physical Status Classification System. A Leksell Gamma Knife Model C with APS was used for all cases. Morphometric characteristics, operative background of the patients and operative data are shown in table 1. Case 1 A 27-kg, 10-year-old boy who had suffered from visual field defects due to compression of the optic chiasma by craniopharyngioma underwent craniotomy at age 3. At age 10, the recurrent intrasellar tumor was removed by Hardy approach and
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GKRS was scheduled 2 months after the operation for the bilateral cavernous sinus tumor which was inaccessible by surgery. The target volume of radiation was 4.0 cm3 with a marginal dose of 12 Gy at the 50% isodose line (fig. 1a). Patient immobilization was crucial, as the radiation area was extremely close to the optic pathway. Because of emotional trauma caused by multiple operations and mental retardation it was deemed prudent to provide general anesthesia. Case 2 A 10-kg, 3-year-old girl, who was diagnosed with cerebellar tumor (pathologically confirmed desmoplastic medulloblastoma) was treated with chemotherapeutics at the age of 1 year and 4 months. Repeated local recurrences had been treated by surgery, conventional radiation therapy (53.8 Gy) and intrathecal chemotherapy. Two months after the last operation, tumor recurrence was found by MRI, though the cytological examination of her cerebrospinal fluid did not show prominent tumor dissemination. GKRS was scheduled to achieve local control of tumor growth, which seemed to be associated with better quality of life. Because the main lesion was located on the left dorsal side of pons, postoperative respiratory disorder was a concern (fig. 1b). General anesthesia with respiratory management was selected considering the tumor location, the patient’s age and mental retardation. Six tumors were treated with a marginal dose of 18 Gy. The target volume ranged from 0.4 to 4.4 cm3 at the 50% isodose line. Case 3 A 20-kg, 4-year-old boy who had experienced an intracranial hematoma due to rupture of an arteriovenous malformation underwent hematoma evacuation and partial resection of the nidus under inhalational general anesthesia. Endovascular embolization was subsequently performed for the residual nidus; however, the following angiography confirmed an incomplete treatment result. GKRS was performed 5 months later to occlude the residual nidus. The target volume was 3.6 cm3, and a marginal dose of 22 Gy was used at the 50% isodose line (fig. 1c). He recovered without any neurological deficits. However, previous emotional trauma, the history of emergence agitation, postoperative nausea and vomiting (PONV) noted in previous anesthesia as well as the ex-
Kamata /Hayashi /Nagata /Muragaki / Iseki /Okada /Ozaki
Color version available online
a Fig. 1 Dose planning images obtained for GKRS. a Craniopharyngioma of case 1 was located in intra-suprasellar region with bilateral cavernous sinus invasion. It was very close to the optic nerve and chiasma (orange). We irradiated only the tumor (12 Gy area: yellow line) with high selectivity excluding the vital structures. The mean dose to the optic apparatus was less than 10 Gy (green line). Color information is available online.
pected longer treatment time indicated that the use of propofolbased general anesthesia was required. Preparation Prior to the treatment, all staff including neurosurgeons, anesthesiologists, nurses, clinical engineers and radiology technicians met several times to determine the sequence, procedure and duration of the treatment. Mobile phone numbers of the staff and a flowchart of the whole procedure were distributed to all staff. All routes were checked and secured to ensure a smooth and safe patient transportation. According to our routine practice, two anesthesiologists, one senior resident and one staff doctor, were assigned to each case. Total intravenous anesthesia with propofol and fentanyl was selected because the equipment for scavenging waste inhalational anesthetics was not available in any location. Propofol was administered by an automated computer-driven target-controlled
Intraoperative Management of Pediatric Gamma Knife Radiosurgery
infusion (TCI) system, which was developed by our group with CodeWarrior Professional release 5 (Metrowerks, Austin, Tex., USA) for Mac OS 9 (Apple Computer, Cupertino, Calif., USA) [6]. This application controls a Graseby 3500 syringe pump (Sims Graseby, Watford, UK) connected via the RS232 serial port and provides the target-controlled infusion of propofol with the information of the predicted blood concentration as well as the effectsite concentration of propofol based on the pharmacokinetic simulation using Marsh model [7]. A prefilled syringe of propofol (1% Diprivan쏐 Injection-kit; AstraZeneca, London, UK) was used for the TCI administration. Standard cardiorespiratory monitoring equipment such as electrocardiogram (ECG), heart rate (HR), peripheral oxygen saturation (SpO2), end-tidal carbon dioxide (EtCO2) and noninvasive blood pressure was employed. In addition, the Bispectral Index (BIS쏐; Covidien, Dublin, Ireland) monitor was used at the anesthesia induction in order to evaluate the effect-site concentra-
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Color version available online
b Fig. 1 Dose planning images obtained for GKRS. b A multiple desmoplastic medulloblastoma was a target lesion for GKRS in case 2. Six tumors were demonstrated on the MRI. The main lesion was a recurrent tumor after surgical resection and was located on the left dorsal side of the pons. All the tumors were irradiated conformally (12 Gy area: yellow line) with high selectivity. Green line is 10 Gy. Color information is available online.
tion of propofol at the loss of consciousness. BIS is the most widely adopted electroencephalogram monitor [8–9], where an index value of 100 corresponds to the awake state and a value of 0 indicates cortical electrical silence. The range of values from 40 to 60 is considered to be adequate for general anesthesia. Following standard care in the operating room (OR) to prevent nerve compression and skin maceration caused by a long procedure, we prepared an egg crate foam mattress pad and a big pillow. All pressure points were padded with pieces of mattress. A pillow was also placed under the knees to reduce the risk of sciatic overextension. Induction of Anesthesia The patient was carried to the induction room without premedication. All monitoring devices were attached as planned. Following peripheral cannulation, 2 g/kg of fentanyl was injected and propofol infusion was commenced at the initial target concentration of 5.0 g/ml with our TCI system. Loss of consciousness was defined as the loss of response to calling and was con-
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firmed by a BIS value below 60. Vecuronium 0.2 mg/kg was used to facilitate tracheal intubation. Ventilation was mechanically controlled to maintain EtCO2 between 30 and 35 Torr. Propofol target concentration was titrated to achieve the BIS value around 50 because we deemed the propofol effect-site concentration at this condition to be optimal for maintenance of anesthesia. Fentanyl was repeatedly injected as necessary according to the surgical stimuli. The stereotactic frame was attached after the BIS selfadhesive EEG electrode strip was detached from the patient’s forehead. A Foley catheter was inserted to measure urine output. Then, the patient was transferred from the induction room to the CT unit along with our propofol TCI system under manual ventilation using the Jackson-Rees circuit. Anesthetic Management during CT Scanning and Angiography All medical equipment required for anesthesia and monitoring was placed beside the patient during CT scanning and angiography. Both the propofol TCI system and the portable display
Kamata /Hayashi /Nagata /Muragaki / Iseki /Okada /Ozaki
Color version available online
c Fig. 1 Dose planning images obtained for GKRS. c In case 3, the residual nidus of a ruptured arteriovenous malformation was located
in the left posterior temporal lobe. We irradiated all the nidus (20 Gy area: yellow line) as much as possible. Green line is 16 Gy. Color information is available online.
monitor were observed from outside of the examination room through a leaded glass window (fig. 2a). Special Consideration in MRI Suite We used only MRI-compatible apparatuses in the imaging room. We chose Titus (Dräger, Lübeck, Germany), an MRI-compatible anesthetic apparatus, for mechanical ventilation. INVIVO Pulse Oximeter 3109-3 (Invivo, Orlando, Fla., USA) was used for evaluation of HR and SpO2. Prior to the treatment, we bored a 10-cm diameter hole in the wall of the MRI suite. All cables, hoses and tubes, which were connected to MRI-incompatible devices, were led through the hole the day before treatment. The TCI system was placed next to the imaging room and we delivered propofol through 8 sequentially connected intravenous extension tubes (each 1.2 m long) because a propofol prefilled syringe could not work under magnetically active conditions. An air hose for noninvasive blood pressure measurement and an
Intraoperative Management of Pediatric Gamma Knife Radiosurgery
EtCO2 sampling tube were also led out. We could not monitor ECG because an MRI-compatible electrocardiograph was not yet available (fig. 2b). Special Consideration during GKRS Taking into consideration the range of motion of the irradiation bed, cables and extension tubes were placed precisely. Propofol delivery was remotely controlled via the hospital local area network (LAN) during GKRS with Timbuktu Pro ver.6 (Motorola, Schaumburg, Ill., USA), a remote control software that allows us to control another computer across the LAN. One computer, which was originally controlling propofol infusion, was left in the radiotherapy room together with our TCI system, and another computer was placed in the control room. Cardiorespiratory information was also transferred to the control room through the hospital LAN. The patient’s condition was checked directly at the intervals between each run (fig. 2c).
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CT unit, neuroangiography suit Infusion pump (Graseby 3500)
Patient
Propofol (RS232 serial port)
Communication cable (length >3 m)
Anesthesiologists
(RS232 serial port)
Laptop computer (Apple PowerBook G3)
Computer
Software: ConGrase TCI (propofol TCI)
a
MRI suite
Intravenous extension tube (sequentially connected 8 tubes, each 1.2 m long)
Infusion pump (Graseby 3500)
Patient Propofol Hole (10 cm in diameter, in the wall of MRI suite)
Fig. 2 Schematic diagram of drug delivery in each treatment room. Schematic diagrams of propofol delivery are presented. Propofol was administered by an automated computer-driven TCI system, ConGraseTCI. In radioactive fields, all medical equipment required for anesthesia was placed beside the patient (a). In MRI suite, all cables, hoses and tubes, which were connected to MRI incompatible devices, were led through the hole. Propofol infusion was controlled continuously from next to the imaging room (b).
Communication cable (length >3 m)
(RS232 serial port)
Laptop computer
Pediatr Neurosurg
Computer
Software: ConGrase TCI
Anesthesiologists
Command
b
Recovery from Anesthesia Propofol was discontinued when the stereotactic frame was removed and the patient was transferred to the induction room. Patients were extubated after they showed some clinical signs of emergence. All cases were managed safely, but APS was not applied to one patient (case 1) due to a mechanical failure. There were no perioperative complications including any signs of intraoperative
6
(RS232 serial port)
awareness, radiation interference, airway management trouble, delayed recovery from anesthesia, emergence agitation or PONV. Postoperative emotional trauma was also evaluated at the postanesthetic rounds, which were performed 1–2 h after irradiation and before discharge from hospital. Neither unordinary facial expression nor the incidence of uncommon behavior during nighttime was observed. All patients were discharged after overnight observation.
Kamata /Hayashi /Nagata /Muragaki / Iseki /Okada /Ozaki
Gamma Knife unit
Infusion pump (Graseby 3500)
Patient
Propofol (RS232 serial port) Communication cable (length >3 m) (RS232 serial port)
Computer Laptop computer Software: ConGrase TCI
Ethernet/LAN 100 Base-Tx
LAN Laptop/desktop computer Computer
Fig. 2 Schematic diagram of drug delivery
in each treatment room. Propofol delivery was remotely controlled via the hospital LAN during GKRS (c).
Anesthesiologists
Ethernet
c
Discussion
With the remarkable development of technological advancement in diagnosis and therapeutic procedures, the demand for general anesthesia performed on children outside the OR has been increasing. In particular, sedation/anesthesia during diagnostic and therapeutic radiology has been recognized as one of the largest fields in pediatric anesthesia [10]. Several studies have suggested that anesthetic management of pediatric interventional radiology is relatively safe [11–13]. Mason et al. [11] proposed that a nurse-provided sedation protocol could become an alternative to an anesthesiologist-managed general anesthesia for pediatric interventional radiological procedures, although the pediatric population receiving sedation/anesthesia in non-OR-based settings is categorized into the highest risk and the lowest error tolerance subgroup [14–15]. GKRS is distinctive among radiological interventions in terms of long duration of surgery due to multiple patient transfers [1–2, 4]. As availability and indications for GKRS are expanding in the pediatric population [16], the demand for general anesthesia is expected to increase. For this reason, we established general anesthesia with a continuous monitoring system for the pediatric patients who should be treated by GKRS. Based on the safety guidelines of perioperative management, all methods we used met the standards mandated for genIntraoperative Management of Pediatric Gamma Knife Radiosurgery
Command
eral anesthesia in the OR [17]; patients were managed by total intravenous anesthesia with propofol TCI, endotracheal intubation was adopted for airway management and all standard monitors were applied. In the case of general anesthesia, there are two choices of anesthetic agents: inhaled volatile anesthetic and an intravenous agent, propofol. Traditionally, general anesthesia with inhalational agents has been the mainstream, but continuous propofol infusion seems to have become an alternative to inhalational anesthesia in pediatric cases. Propofol allows rapid onset and offset of action [18] and reduces the incidence of delirium or emergence agitation [19] as well as of PONV [20]. No patient in the current series presented emergence agitation or PONV, although one patient (case 3) had a history of emergence agitation and repeated vomiting in previous anesthesia with an inhaled volatile agent. Furthermore, the use of a portable intravenous infusion device does not cause any propofol infusion suspension. These profiles of continuous propofol infusion meet our requirements completely. For propofol delivery, TCI has been recognized as a much superior method to manual infusion [21–23], because we can directly control propofol concentrations as the target values for its administration. Jeleazcov et al. [24] have reported that the effect-site concentration of propofol showed a close relationship with the BIS value. In addition, in children aged from 3 months to 9 years, individPediatr Neurosurg
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ual propofol concentrations at loss of consciousness were similar to those at awakening [25]. Intraoperative awareness should be avoided. It has been suggested that the experience of intraoperative awareness correlates well with postoperative emotional trauma, which had a higher incidence reported in pediatrics than in adults [26]. Therefore, we considered that a propofol concentration that requires achieving the BIS value around 50 might secure the patient’s state of unconsciousness. Actually, no signs of intraoperative awareness were observed in the current series. Airway management is another major issue. Children are at higher risk for respiratory depression and life-threatening hypoxia due to their physiological features [27]. Cravero et al. [10] have reported that the incidence of serious adverse events outside the OR is low but that potentially harmful minor events occurred once in 89 pediatric cases. Most of the adverse events were related to upper airway troubles; unplanned airway interventions were frequently required. In the case of GKRS, its stereotactic device restricts free access to the patient’s airway. Endotracheal intubation seems impossible when the frame is already fixed to the patient’s head. Even simple procedures like changing head position or chin lifting are challenging. Moreover, the safety system of Gamma Knife itself could hinder prompt treatment of upper airway troubles if a respiratory deterioration is observed. We thus considered that endotracheal intubation is the best way, which ensures the airway patency for children undergoing GKRS. The type of endotracheal tube should also be considered because it could probably disturb the surgical approach. We used an RAE쏐 tube for the current series [28]. The unique acute-angle bend shape of the tube allowed it to be fixed to the immediate area around the face and eliminated incidental tube kinking. Monitoring the patient’s vital signs has been a frequent concern during non-OR-based settings. Careful preparation in magnetically active environments seems to be more vital than in radioactive fields. While no accidental deaths were reported from the multiple center survey [10], there is one report stating that the mortality risk doubled when general anesthesia was performed in an MRI suite [29]. As the MRI-compatible precise ECG monitor is still unavailable, it has been truly difficult to set everything up like the OR. Our patients were anesthetized and their vital signs were continuously recorded except for ECG. Although we could not monitor either real ECG waves or precise HR, pulse oximeter was substitutable; HR was replaced by pulse rate monitoring and 8
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cardiac rhythm was also inferred from pulse wave regularity. We did not experience either adverse events or low-quality imaging. In the Gamma Knife unit, we visualized the patient via a closed-circuit television camera, and all cardiorespiratory information was transferred from inside of the radiotherapy room to the control room through the hospital LAN. This technique was also applied to the remote control propofol delivery system. Though Timbuktu was used as remote control software under Mac OS 9, our strategy is practical because several kinds of remote control software are now available. Although we should be mindful of network-related security problems, either optical or wireless communication is also functionally competent for data transfer from magnetic field. Technical advancement of the planning software (Leksell Gamma Plan; Elekta Instruments AB) has enabled us to utilize all imaging modalities, including frameless MRI studies. This latest software could also support remote control dose planning through an online patient database. Thus, these improvements to the dose planning system have successfully reduced physiological distress of the patients prior to treatment; however, the development of irradiation itself leaves some critical problems for the anesthetized patients as mentioned earlier. General anesthesia is not necessarily applied only to pediatric cases. Claustrophobia, anxiety and panic attacks are recognized as the most disabling psychological phenomena experienced by the patients who undergo MRI as well as GKRS [30–31]. Two percent of the patients manifested significant physiological stress during GKRS, and 2 of 9 traumatic patients developed severe cardiac events, consisting of myocardial infarction and ischemic chest pain from aortic stenosis [32]. As Vachhrajani et al. [32] have suggested, patients with comorbid medical problems should be evaluated for their requirement of sedation/anesthesia to reduce treatment-induced physiological stress. Therefore, we propose that all patients, including adults, who have emotional stress associated with treatment, should be managed with general anesthesia safely and effectively. Moreover, general anesthesia with respiratory management can be an alternative method for the patient whose pathological lesion seems to lead easily to respiratory disorder after GKRS (case 2). Our remote control system would be indispensable especially for the new generation of GKRS. We confirmed that our remotely controlled monitoring and anesthesia system could provide reliable intraoperative care to the pediatric patients who received GKRS Kamata /Hayashi /Nagata /Muragaki / Iseki /Okada /Ozaki
with an automated setting. All patients could be managed safely and any perioperative complications were observable. Medical personnel can remain outside the treatment room during irradiation because this system allowed us to leave the anesthetized patient alone. Based on our experience, this remote control system will significantly contribute to future progress in GKRS.
Acknowledgements We thank Masao Usukura (radiology technician; Department of Neuroradiology) and Yuki Usuba (nurse; Department of Neuroradiology, Division of Gamma Knife) of Tokyo Women’s Medical University for invaluable help in the technical support. The authors are also indebted to Ryoko Zaitsu and Ken Sakamoto (clinical engineers) of the Division of Clinical Engineer of Tokyo Women’s Medical University for their contribution to this project.
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22 McFarlan CS, Anderson BJ, Short TG: The use of propofol infusions in paediatric anaesthesia: a practical guide. Paediatr Anaesth 1999;9:209–216. 23 Kataria BK, Ved SA, Nicodemus HF, Hoy GR, Lea D, Dubois MY, Mandema JW, Shafer SL: The pharmacokinetics of propofol in children using three different data analysis approaches. Anesthesiology 1994; 80: 104– 122. 24 Jeleazcov C, Ihmsen H, Schmidt J, Ammon C, Schwilden H, Schüttler J, Fechner J: Pharmacodynamic modelling of the bispectral index response to propofol-based anaesthesia during general surgery in children. Br J Anaesth 2008;100:509–516. 25 McCormack J, Mehta D, Peiris K, Dumont G, Fung P, Lim J, Ansermino JM: The effect of a target controlled infusion of propofol on predictability of recovery from anesthesia in children. Paediatr Anaesth 2010;20:56–62. 26 Blussé van Oud-Alblas HJ, van Dijk M, Liu C, Tibboel D, Klein J, Weber F: Intraoperative awareness during paediatric Anaesthesia. Br J Anaesth 2009;102:104–110. 27 Committee on Drugs: American Academy of Pediatrics: Guidelines for monitoring and management of pediatric patients during and after sedation for diagnostic and therapeutic procedures: addendum. Pediatrics 2002;110:836–838. 28 Ring WH, Adair JC, Elwyn RA: A new pediatric endotracheal tube. Anesth Analg 1975; 54:273–274. 29 Girshin M, Shapiro V, Rhee A, Ginsberg S, Inchiosa MA Jr: Increased risk of general anesthesia for high-risk patients undergoing magnetic resonance imaging. J Comput Assist Tomogr 2009;33:312–315. 30 Chung SM: Safety issues in magnetic resonance imaging. J Neuroophthalmol 2002;22: 35–39. 31 Clifford W, Sharpe H, Khu KJ, Cusimano M, Knifed E, Bernstein M: Gamma Knife patients’ experience: lessons learned from a qualitative study. J Neurooncol 2009;92:387– 392. 32 Vachhrajani S, Fawaz C, Mathieu D, Ménard C, Cusimano M, Gentili F, Hodaie M, Kenny B, Kulkarni AV, Laperriere N, Schwartz M, Tsao M, Bernstein M: Complications of Gamma Knife surgery: an early report from 2 Canadian centers. J Neurosurg 2008;109:2–7.
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