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Stereotactic Neutron Radiosurgery for Arteriovenous Malformations of the Brain
Medical Dosimery, Vol. 13, pp. 179-182 Printed in the U.S.A. All rights reserved.
STEREOTACTIC
Copyright
0
1988 American
0739-021 l/88 Association of Medical
$3.00 t .OO Dosimetrists
NEUTRON RADIOSURGERY FOR ARTERIOVENOUS MALFORMATIONS OF THE BRAIN
BRIAN R. GRIFFIN, M.D.*?, SHARON HUMMEL WARCOLA, R.T.T.?, MARC R. MAYBERG, M.D.?, JURI EENMAA, PH.D.*, JOSEPHESKRIDGE,M.D.-f& and H. RICHARD WINN, M.D.-f Abstract-A technique employing single fraction neutron radiosurgery for treatment of intracranial vascular malformations has been developed at the University of Washington and is described in this report. The natural history of arteriovenous malformations of the brain is briefly reviewed, along with currently available therapeutic methods for treatment of these lesions. The characteristics of the neutron beam used for radiosurgery are described, along with methods for patient immobilization, radiation treatment planning, dosimetry, and delivery of treatment using this technique.
capacitating in these patients. Recurrent bleeding is a common problem in AVM patients. Recurrent hemorrhages have a mortality rate of 10 to 20%, l2 and produce neurologic disability in 30% of survivors. lo Stereotactic radiosurgery is the technique of delivery of a large dose of ionizing radiation in a single or very small number of fractions to a precisely defined intracranial volume. First described by LekselLs stereotactic radiosurgery has been used to treat a variety of neurological disorders. Several different radiosurgery methods have been developed, including a gamma unit which employs multiple fixed beams generated by cobalt 60 sources9 multiple noncoplanar rotational arc x-ray fields generated by a linear accelerator4*5 and heavy particle beams (protons, helium ions) generated by cyclotrons7 and synchrocyclotr0ns.i~” All these techniques rely on precisely collimated radiation beams which intersect on the target volume and have a steep dose gradient at the beam edge. This permits a very high dose to be delivered to a sharply circumscribed volume; structures adjacent to the target receive relatively little radiation. This report describes the technique of stereotactic neutron radiosurgery developed at the University of Washington.
INTRODUCIION
Arteriovenous malformations (AVMs) of the brain are congenital lesions which are composed of a tangled mass of dilated and tortuous blood vessels. Arterial channels in the malformation are continuous with dilated cerebral veins, comprising an arteriovenous shunt. AVMs may cause severe neurological problems, including disabling or lethal intracranial hemorrhages, severe headache, seizures, and progressive neurological deficits. Neurosurgical excision is the preferred form of therapy for AVMs located in accessible areas of the central nervous system. However, approximately one-third of all AVMs are located deep in the brain, and surgical removal of these lesions is often inadvisable due to the risks of irreversible neurological damage associated with operating on these patients. The prevalence of AVMs in the general population is uncertain, since many lesions remain asymptomatic throughout life and are only detected at autopsy. It is estimated that over one million Americans may harbor unsuspected AVMs. Intracranial hemorrhage is the most common initial presentation of AVMs, and occurs in approximately half of all symptomatic cases.2,6 Young adults are most commonly affected, and the severity of neurological damage associated with the hemorrhage ranges from mild headache to coma and death. Although neurological recovery can occur, functional deficitsare often severe and irreversible after a bleed. Headaches, seizures, and progressive loss of neurolog-
TECHNIQUE
Neutron beams are generated by the medically dedicated cyclotron in University Hospital at the University of Washington (Fig. 1). This device produces fast neutron beams of 25 MeV average energy. The dose distributions from these neutron beams are similar to photon beams produced by a 6 MeV linear
ical function due to “steal” of blood from vital adjacent areas of the brain by the AVM may be in-
* Department of Radiation Oncology, University Seattle, WA. t Department of Neurological Surgery, University ington, Seattle, WA.
+ Department tie, WA.
of Wash-
ington,
of Wash-
179
of Radiology,
University
of Washington,
Seat-
180
Medical Dosimetry
Fig. 1. Isocentric gantry at University of Washington pital cyclotron.
Hos-
accelerator. The neutron fields are collimated by either the standard multileaf collimation system, which can provide irregularly shaped (continuously variable and stepped) field sizes as small as 12.5 mm, or by fixed-size extension tubes projecting circular fields ranging from 10 to 25 mm. The treatment beam is isocentrically mounted and has an alignment precision approaching 2 mm. This isocentric capability allows treatment to be delivered through a large number of portals and the dose delivered through each portal to be minimized. The total scattered dose outside of the treatment beam for a single field is less than 2% of that at dose maximum. A thermoplastic immobilization mask is constructed for each patient (Fig. 2); which is joined to a stereotactic localization device this system is patterned on previously described techniques. ‘J * The mask and localization device assembly is precisely indexed to the treatment unit. Computed tomography (CT) and magnetic resonance (MR) scans are performed in the treatment position with the patient in the immobilization mask and localization device;
Fig. 2. Theremoplastic immobilization mask with stereotactic localization device.
Volume 13, Number 4, 1988
prior to scanning, lasers on each machine are checked for proper alignment. Horizontal and vertical bars on the mask frame are aligned with the scanner lasers. If necessary, the frame of the mask is shimmed to correct any misalignment of the system. The origin of the CT or MR scan is then marked on the mask both on the anterior surface and lateral surfaces. These marks are used for a three point setup when the patient is positioned for treatment. CT and MR axial images are obtained at 3 mm intervals through the AVM and immediately adjacent brain, while the remainder of the brain is scanned at 10 mm intervals. After completion of the scan patient position is rechecked to ensure that no patient movement occurred during the scan; the scan is repeated if there is any uncertainty concerning alignment of the system. The CT study is transferred via magnetic tape to a VAX 1 l-780 computer in the Department of Radiation Oncology and the images are displayed using the Plan-32 treatment planning system (Oncology Systems, Inc., Bellevue, WA). Using this system the patient’s contour is outlined on each of the approximately 35 CT slices, along with the patient’s eyes on the images where they are present. Using the MR scan and a previously performed angiogram for guidance, the radiation oncologist in conjunction with a neuroradiologist defines the AVM volume; the target volume is then outlined on each CT slice where it is present. A plan is then constructed employing nine noncoplanar, nonopposing isocentric fields. Treatment planning considerations include: excluding the eyes from entrance and exit areas of all portals, avoiding the frame rods to minimize beam attenuation, and maximizing the separation between portals to avoid overlap between beams away from the target volume. The beams-eye view capabilities (Fig. 3) of the treatment planning system are essential for selecting the isocenter and determining optimal field configurations. By enabling the three-dimensional shape of the AVM to be depicted in any oblique plane, the pro-
Fig. 3. Beams-eye view of vertex field.
Stereotactic neutron radiosurgery 0 B. R. GRIFFIN
gram makes shaping of each neutron beam possible using the variable collimator in the cyclotron gantry (Fig. 4). After defining initial anterior, lateral, and vertex fields, a balloon diagram (Fig. 5) is used to assist field design for the remaining portals. Equal weighting is used for all nine fields, and the total dose is specified at the isocenter. The three dimensional dose distribution is determined throughout the volume of the AVM and adjacent brain; fields may be modified to skew the high dose volume from critical brain structures (Fig. 6). After the plan is finalized a complete simulation of the treatment is performed in the treatment room. The mask frame and mask are aligned and fastened to the treatment couch to simulate the patient’s setup and the accuracy of all gantry and couch motions and readout scales (in mm) are verified. The isocenter is located by shifting from the CT scan origin marked on the mask at the time of the CT study. Each treatment field is set up as specified in the treatment plan. Field outline and number are marked on the mask, allowing modification of the plan prior to treatment should any problems (e.g. field overlap on the mask surface) be evident. Treatment is given in a single fraction over a two hour period; 900 cGy is delivered to the target volume. An intravenous muscle relaxant is administered to patients to prevent cramping and ease anxiety; general anesthesia may be used when IV muscle relaxants are inadequate. Low dose steroid therapy is
et al.
181
ANTERIOR INFERIOR
RIGHT
SUPERIOR
INFERIOR
LEFT
urntable
?I
w INFERIOR
Gantry LEFT
SUPERIOR
LEFT
POSTERIOR
Fig. 5. Balloon diagram showing field relationships and beam pathways. The X and Y axis of the diagram are tumtable angle and gantry angle respectively. Use of the diagram allows visualization of where a field may be placed to avoid overlap in the entrance or exit of another field. As fields are diagrammed, locations of other possible fields are apparent.
initiated several days prior and is discontinued shortly are treated on an outpatient several hours after treatment
Fig. 4. Variable collimator.
RIGHT
to neutron radiosurgery after treatment. Patients basis, and return home is delivered.
Fig. 6. Axial CT slice with isodoses depicted. Isodoses are displayed throughout the three dimensional volume of lesion and adjacent brain.
182
Medical Dosimetry
CONCLUSION
The treatment planning aspects of a newly developed technique of radiosurgery for intracranial AVMs are presented in this paper. Fifteen patients have been treated with this technique to date; clinical results in the initial group of these patients have been reported elsewhere.3 REFERENCES 1. Fabrikant, J.; Lyman, J.; Hosobuchi, Y. Stereotactic heavy-ion Bragg peak radiosurgery for intracranial vascular disorders: method for treatment of deep arteriovenous malformations. Br. J. Radiol. 57~479-490; 1984. 2. Graf, C.J.; Perret, G.E.; Tomer, J.C. Bleeding from cerebral arteriovenous malformations as part of their natural history. J. Neurosurg. 58:331-337; 1983. 3. Griffin, B.R.; Eskridge, J.; Mayberg, M.; Eenmaa, J.; Winn,
H.R. Particle beam radiosurgery for intracranial arteriovenous malformations. Am. J C/in. One. (in press). 4. Hartmann, G.; Schegel, W.; Sturm, V.; Kober, B.; Pastyr, 0.; Lorenz, W. Cerebral radiation surgery using moving field irra-
Volume 13, Number 4, 1988 diation at a linear accelerator facility. Znt. J. Radiat. Oncol. Biol. Phys. 11:1185-l 192; 1985. 5. Heifetz, M.; Wexler, M.; Thompson, R. Single-beam radiotherapy knife. A practical theoretical mode. J. Neurosurg. 60:814-818; 1984. 6. Hook, 0.; Johanson, C. Intracranial arteriovenous aneurysms.
A follow-up study with particular attention to their growth. 1958. 7. Kjellberg, R.; Hanamura, T.; Davis, K.; Lyons, L.; Adams, R. Bragg-peak proton beam therapy for arteriovenous malformations of the brain. New Engl. J. Med. 309:269-274; 1983. 8. Leksell, L. The stereotaxic method and radiosurgery of the brain. Acta Chir. Scan. 102:316-319; 1951. 9. Leksell, L. Stereotaxis and radiosurgery. An operative system. Charles Thomas, Springfield, 197 1. 10. Leussenshop, A.J.; Mujica, P.H. Embolization of segments of the circle of Willis and adjacent branches for management of certain inoperable cerebral arteriovenous malformations. J. Arch. Neurol. Psychiatry. 80:39-54;
Neurosurg. 54573-582;
1981.
11. Lyman, J.T.; Kanstein, L.; Yeater, F.; Fabrikant, J.; Frankel, K. A helium-ion beam for stereotactic radiosurgery of central nervous system disorders. Med. Phys. 13(5):695-699; 1986. 12. Perret, G.; Nishioka, H. Report on the cooperative study of intracranial aneurysms and subarachnoid hemorrhage. Section VCI. Arteriovenous malformations. J. Neurosurg. 25:467-490: 1986.
STEREOTACTIC
Copyright
0
1988 American
0739-021 l/88 Association of Medical
$3.00 t .OO Dosimetrists
NEUTRON RADIOSURGERY FOR ARTERIOVENOUS MALFORMATIONS OF THE BRAIN
BRIAN R. GRIFFIN, M.D.*?, SHARON HUMMEL WARCOLA, R.T.T.?, MARC R. MAYBERG, M.D.?, JURI EENMAA, PH.D.*, JOSEPHESKRIDGE,M.D.-f& and H. RICHARD WINN, M.D.-f Abstract-A technique employing single fraction neutron radiosurgery for treatment of intracranial vascular malformations has been developed at the University of Washington and is described in this report. The natural history of arteriovenous malformations of the brain is briefly reviewed, along with currently available therapeutic methods for treatment of these lesions. The characteristics of the neutron beam used for radiosurgery are described, along with methods for patient immobilization, radiation treatment planning, dosimetry, and delivery of treatment using this technique.
capacitating in these patients. Recurrent bleeding is a common problem in AVM patients. Recurrent hemorrhages have a mortality rate of 10 to 20%, l2 and produce neurologic disability in 30% of survivors. lo Stereotactic radiosurgery is the technique of delivery of a large dose of ionizing radiation in a single or very small number of fractions to a precisely defined intracranial volume. First described by LekselLs stereotactic radiosurgery has been used to treat a variety of neurological disorders. Several different radiosurgery methods have been developed, including a gamma unit which employs multiple fixed beams generated by cobalt 60 sources9 multiple noncoplanar rotational arc x-ray fields generated by a linear accelerator4*5 and heavy particle beams (protons, helium ions) generated by cyclotrons7 and synchrocyclotr0ns.i~” All these techniques rely on precisely collimated radiation beams which intersect on the target volume and have a steep dose gradient at the beam edge. This permits a very high dose to be delivered to a sharply circumscribed volume; structures adjacent to the target receive relatively little radiation. This report describes the technique of stereotactic neutron radiosurgery developed at the University of Washington.
INTRODUCIION
Arteriovenous malformations (AVMs) of the brain are congenital lesions which are composed of a tangled mass of dilated and tortuous blood vessels. Arterial channels in the malformation are continuous with dilated cerebral veins, comprising an arteriovenous shunt. AVMs may cause severe neurological problems, including disabling or lethal intracranial hemorrhages, severe headache, seizures, and progressive neurological deficits. Neurosurgical excision is the preferred form of therapy for AVMs located in accessible areas of the central nervous system. However, approximately one-third of all AVMs are located deep in the brain, and surgical removal of these lesions is often inadvisable due to the risks of irreversible neurological damage associated with operating on these patients. The prevalence of AVMs in the general population is uncertain, since many lesions remain asymptomatic throughout life and are only detected at autopsy. It is estimated that over one million Americans may harbor unsuspected AVMs. Intracranial hemorrhage is the most common initial presentation of AVMs, and occurs in approximately half of all symptomatic cases.2,6 Young adults are most commonly affected, and the severity of neurological damage associated with the hemorrhage ranges from mild headache to coma and death. Although neurological recovery can occur, functional deficitsare often severe and irreversible after a bleed. Headaches, seizures, and progressive loss of neurolog-
TECHNIQUE
Neutron beams are generated by the medically dedicated cyclotron in University Hospital at the University of Washington (Fig. 1). This device produces fast neutron beams of 25 MeV average energy. The dose distributions from these neutron beams are similar to photon beams produced by a 6 MeV linear
ical function due to “steal” of blood from vital adjacent areas of the brain by the AVM may be in-
* Department of Radiation Oncology, University Seattle, WA. t Department of Neurological Surgery, University ington, Seattle, WA.
+ Department tie, WA.
of Wash-
ington,
of Wash-
179
of Radiology,
University
of Washington,
Seat-
180
Medical Dosimetry
Fig. 1. Isocentric gantry at University of Washington pital cyclotron.
Hos-
accelerator. The neutron fields are collimated by either the standard multileaf collimation system, which can provide irregularly shaped (continuously variable and stepped) field sizes as small as 12.5 mm, or by fixed-size extension tubes projecting circular fields ranging from 10 to 25 mm. The treatment beam is isocentrically mounted and has an alignment precision approaching 2 mm. This isocentric capability allows treatment to be delivered through a large number of portals and the dose delivered through each portal to be minimized. The total scattered dose outside of the treatment beam for a single field is less than 2% of that at dose maximum. A thermoplastic immobilization mask is constructed for each patient (Fig. 2); which is joined to a stereotactic localization device this system is patterned on previously described techniques. ‘J * The mask and localization device assembly is precisely indexed to the treatment unit. Computed tomography (CT) and magnetic resonance (MR) scans are performed in the treatment position with the patient in the immobilization mask and localization device;
Fig. 2. Theremoplastic immobilization mask with stereotactic localization device.
Volume 13, Number 4, 1988
prior to scanning, lasers on each machine are checked for proper alignment. Horizontal and vertical bars on the mask frame are aligned with the scanner lasers. If necessary, the frame of the mask is shimmed to correct any misalignment of the system. The origin of the CT or MR scan is then marked on the mask both on the anterior surface and lateral surfaces. These marks are used for a three point setup when the patient is positioned for treatment. CT and MR axial images are obtained at 3 mm intervals through the AVM and immediately adjacent brain, while the remainder of the brain is scanned at 10 mm intervals. After completion of the scan patient position is rechecked to ensure that no patient movement occurred during the scan; the scan is repeated if there is any uncertainty concerning alignment of the system. The CT study is transferred via magnetic tape to a VAX 1 l-780 computer in the Department of Radiation Oncology and the images are displayed using the Plan-32 treatment planning system (Oncology Systems, Inc., Bellevue, WA). Using this system the patient’s contour is outlined on each of the approximately 35 CT slices, along with the patient’s eyes on the images where they are present. Using the MR scan and a previously performed angiogram for guidance, the radiation oncologist in conjunction with a neuroradiologist defines the AVM volume; the target volume is then outlined on each CT slice where it is present. A plan is then constructed employing nine noncoplanar, nonopposing isocentric fields. Treatment planning considerations include: excluding the eyes from entrance and exit areas of all portals, avoiding the frame rods to minimize beam attenuation, and maximizing the separation between portals to avoid overlap between beams away from the target volume. The beams-eye view capabilities (Fig. 3) of the treatment planning system are essential for selecting the isocenter and determining optimal field configurations. By enabling the three-dimensional shape of the AVM to be depicted in any oblique plane, the pro-
Fig. 3. Beams-eye view of vertex field.
Stereotactic neutron radiosurgery 0 B. R. GRIFFIN
gram makes shaping of each neutron beam possible using the variable collimator in the cyclotron gantry (Fig. 4). After defining initial anterior, lateral, and vertex fields, a balloon diagram (Fig. 5) is used to assist field design for the remaining portals. Equal weighting is used for all nine fields, and the total dose is specified at the isocenter. The three dimensional dose distribution is determined throughout the volume of the AVM and adjacent brain; fields may be modified to skew the high dose volume from critical brain structures (Fig. 6). After the plan is finalized a complete simulation of the treatment is performed in the treatment room. The mask frame and mask are aligned and fastened to the treatment couch to simulate the patient’s setup and the accuracy of all gantry and couch motions and readout scales (in mm) are verified. The isocenter is located by shifting from the CT scan origin marked on the mask at the time of the CT study. Each treatment field is set up as specified in the treatment plan. Field outline and number are marked on the mask, allowing modification of the plan prior to treatment should any problems (e.g. field overlap on the mask surface) be evident. Treatment is given in a single fraction over a two hour period; 900 cGy is delivered to the target volume. An intravenous muscle relaxant is administered to patients to prevent cramping and ease anxiety; general anesthesia may be used when IV muscle relaxants are inadequate. Low dose steroid therapy is
et al.
181
ANTERIOR INFERIOR
RIGHT
SUPERIOR
INFERIOR
LEFT
urntable
?I
w INFERIOR
Gantry LEFT
SUPERIOR
LEFT
POSTERIOR
Fig. 5. Balloon diagram showing field relationships and beam pathways. The X and Y axis of the diagram are tumtable angle and gantry angle respectively. Use of the diagram allows visualization of where a field may be placed to avoid overlap in the entrance or exit of another field. As fields are diagrammed, locations of other possible fields are apparent.
initiated several days prior and is discontinued shortly are treated on an outpatient several hours after treatment
Fig. 4. Variable collimator.
RIGHT
to neutron radiosurgery after treatment. Patients basis, and return home is delivered.
Fig. 6. Axial CT slice with isodoses depicted. Isodoses are displayed throughout the three dimensional volume of lesion and adjacent brain.
182
Medical Dosimetry
CONCLUSION
The treatment planning aspects of a newly developed technique of radiosurgery for intracranial AVMs are presented in this paper. Fifteen patients have been treated with this technique to date; clinical results in the initial group of these patients have been reported elsewhere.3 REFERENCES 1. Fabrikant, J.; Lyman, J.; Hosobuchi, Y. Stereotactic heavy-ion Bragg peak radiosurgery for intracranial vascular disorders: method for treatment of deep arteriovenous malformations. Br. J. Radiol. 57~479-490; 1984. 2. Graf, C.J.; Perret, G.E.; Tomer, J.C. Bleeding from cerebral arteriovenous malformations as part of their natural history. J. Neurosurg. 58:331-337; 1983. 3. Griffin, B.R.; Eskridge, J.; Mayberg, M.; Eenmaa, J.; Winn,
H.R. Particle beam radiosurgery for intracranial arteriovenous malformations. Am. J C/in. One. (in press). 4. Hartmann, G.; Schegel, W.; Sturm, V.; Kober, B.; Pastyr, 0.; Lorenz, W. Cerebral radiation surgery using moving field irra-
Volume 13, Number 4, 1988 diation at a linear accelerator facility. Znt. J. Radiat. Oncol. Biol. Phys. 11:1185-l 192; 1985. 5. Heifetz, M.; Wexler, M.; Thompson, R. Single-beam radiotherapy knife. A practical theoretical mode. J. Neurosurg. 60:814-818; 1984. 6. Hook, 0.; Johanson, C. Intracranial arteriovenous aneurysms.
A follow-up study with particular attention to their growth. 1958. 7. Kjellberg, R.; Hanamura, T.; Davis, K.; Lyons, L.; Adams, R. Bragg-peak proton beam therapy for arteriovenous malformations of the brain. New Engl. J. Med. 309:269-274; 1983. 8. Leksell, L. The stereotaxic method and radiosurgery of the brain. Acta Chir. Scan. 102:316-319; 1951. 9. Leksell, L. Stereotaxis and radiosurgery. An operative system. Charles Thomas, Springfield, 197 1. 10. Leussenshop, A.J.; Mujica, P.H. Embolization of segments of the circle of Willis and adjacent branches for management of certain inoperable cerebral arteriovenous malformations. J. Arch. Neurol. Psychiatry. 80:39-54;
Neurosurg. 54573-582;
1981.
11. Lyman, J.T.; Kanstein, L.; Yeater, F.; Fabrikant, J.; Frankel, K. A helium-ion beam for stereotactic radiosurgery of central nervous system disorders. Med. Phys. 13(5):695-699; 1986. 12. Perret, G.; Nishioka, H. Report on the cooperative study of intracranial aneurysms and subarachnoid hemorrhage. Section VCI. Arteriovenous malformations. J. Neurosurg. 25:467-490: 1986.