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C H A P T E R 4 8 oracic Spinal Stenosis
315
Prognosis after surgery depends on the extent of compression and neurological deficit. Recurrent stenosis has been documented, making routine
follow-up necessary.
20
For thoracic stenosis due to OPLL, multiple treatment options have
been described, including laminectomy, laminoplasty, resection of the PLL,
anterior decompression and fusion via thoracotomy, and posterior decompression and fusion.
ported by a recent long-term study.
21,22
Anterior decompression with fusion has been sup-
23
Fujimura et al reviewed the data of 33
patients followed for more than 5 years after anterior decompression and
fusion was performed for myelopathy in the thoracic spine due to ossification of the PLL. Their results suggested that anterior decompression with
fusion can lead to favorable long-term results. They indicated, however, that
patients with OPLL that affects multiple levels and those with concurrent
OLF may not do as well in long-term follow-up.
Posterior surgical approaches provide an alternative treatment option for
myelopathy due to OPLL, particularly when there is also OLF. It is suggested that, for OPLL, posterior decompression alone may not be sufficient
due to draping of the spinal cord over the kyphotic thoracic spine. Some
advocate a circumferential decompression through an isolated posterior
approach.
24
High complication rates have been documented with this treatment, however, particularly when more than five levels are decompressed.
In a study by Masahiko et al, as many as 33% of patients had deterioration
in their neurological status following surgery. Both the relatively avascular
nature of the thoracic spinal cord and adhesion of dural sac to the PLL are
thought to contribute to these complications. Even higher rates of neurological deterioration have been seen with laminectomy alone, while lower rates
have been reported with posterior decompression and fusion.
25
In theory,
performing a laminectomy without fusion further destabilizes the spine and
subjects the injured spinal cord to additional stresses that lead to a further
decline in neurological function. Masashi et al suggested that in the neurologically intact patient, resection of the PLL is an acceptable treatment,
but for patients with preoperative spinal cord injury, removal of the PLL
increases the risk of paralysis.
26
Many patients with thoracic disc herniations are asymptomatic. When
symptoms do exist, unlike patients with OPLL and OLF, conservative treatment and time can be sufficient to treat the majority of herniations. Modification of activities, physical therapy, and the careful use of nonsteroidal
antiinflammatory drugs are the mainstays of conservative care. The literature suggests that less than 2% of thoracic discs require surgical treatment.
27
When conservative care fails to alleviate symptoms after 4 to 6 weeks, a neurological deficit progresses, or there is evidence of worsening myelopathy,
surgical treatment is warranted.
Operative care of patients with thoracic disc herniations requires assessing several factors to determine operative risk and approach. Depending
on the location and nature of the disc herniation, anterior, thoracoscopic,
lateral, or posterior approaches may be used, the details of which are largely
beyond the scope of this chapter. In general, anteriorlyoriented lesions
require a direct ventral approach such as a transthoracic, thoracoscopic,
or posterolateral (e.g., costotransversectomy, extracavitary) technique for
safe resection that avoids cord manipulation, with bony reconstruction
as necessary. Pulmonary function tests should be performed on patients
with questionable pulmonary reserve if thoracotomy is considered. Discal
calcifications, which are more common in the thoracic spine,
28
are associated with a greater degree of dural adhesion or associated dural calcification. Such information is important for the treating surgeon in deciding
how much disc to remove from the dura, and whether concomitant dural
resection needs to be considered. Once in the operating room, it is essential to identify the correct disc for resection. Sagittal CT reconstructions
or MR images are essential to determine the appropriate level, and plain
radiography or fluoroscopy in the operating room is standard practice for
localization.
For most lateral soft disc herniations, the preferred approach is posterior and usually involves a pediculofacetectomy, typically perfomed by
transpedicular or transfacet technique rather than laminectomy. Significant complications have been reported with posterior laminectomy alone,
29
including cord contusion and lack of improvement of symptoms. The
need for fusion following thoracic disc removal remains controversial but
generally depends on the assessed degree of stability of the region following decompression. It may be beneficial to resect a significant amount of
vertebral body in cases of multilevel disc disease, or when the disc is in
the lower thoracic spine, which may render the spine unstable and require
secondary fusion.
OTHER CAUSES FOR THORACIC SPINAL STENOSIS
Neoplasms
Both intramedullary and extramedullary spinal cord tumors can lead to
thoracic myelopathy and must be considered as a possible etiology in every
older patient with thoracic spinal stenosis. In their experience treating 78
patients with intramedullary spinal cord tumors, Sandalcioglu et al found
that 32% of the tumors were located in the thoracic spine. Low-grade neuroepithelial tumors, ependymomas, astrocytomas, vascular tumors, and
metastatic lesions were identified. The most important predictor of postoperative neurological status was a patient’s preoperative neurological func-
30
tion.
Compared to patients with intramedullary tumors in the cervical
or lumbar spine, these authors found that those with thoracic lesions had
a higher surgical morbidity. This most likely reflects the regional vulnerability of the thoracic cord due to tenuous blood supply, constricted canal
anatomy, and kyphosis. When intramedullary spinal cord tumors are identified, decompression and tumor removal can be performed by laminectomy
or laminoplasty.
Metastatic disease to the thoracic spine is more common than metastasis to the cervical or lumbar spine, due to the greater relative size and bony
blood supply of the thoracic region. Lesions from lung, breast, prostate,
and gastrointestinal carcinomas, as well as other tumor types, are known
to metastasize to the thoracic spine. Until recently, many authors could not
define the best mode of treatment for extramedullary spinal cord tumors
with cord compression causing neurological symptoms. Earlier studies
looking at laminectomy alone or laminectomy in combination with radiotherapy did not show surgery to be beneficial.
31-33
The importance of surgical decompression, however, was shown in a randomized multicenter trial
by Patchell et al, who compared the outcomes of 101 patients treated with
either radiotherapy alone or a combination of radiotherapy and decompressive surgery.
34
All but 13 of the patients had tumors in the thoracic
spine. The median age of their study group was 60. The authors found
that patients treated with a combination of postoperative radiotherapy and
decompressive surgery were significantly better in terms of ambulatory status, functionality, maintenance of urinary continence, strength, and overall
survival than those treated with radiation alone. Their data also suggested
that laminectomy may not always be the best mode of treatment. Rather,
approaching the lesion directly: anterior tumors anteriorly, posterior tumors
posteriorly, and lateral tumors laterally may offer the best results for decompression (see Figure 48-6).
Synovial Cysts
Rare cases of synovial cysts leading to thoracic myelopathy have been
reported. Graham et al outlined a case in which a 54-year-old woman
developed right lower extremity weakness secondary to a cyst at T11-12.35
The cyst was successfully excised via a laminectomy and the patient had a
full recovery. Aspiration has been used as a treatment for synovial cysts in
the lumbar spine and might prove to be a useful treatment option in the
thoracic spine.
PROGNOSIS
An understanding of the long-term results of surgical treatment of thoracic
spinal stenosis due to OLF is limited due to the lack of sufficient study. The
literature suggests that a number of factors may make surgical outcomes
less favorable. These include a longer duration of symptoms prior to decom-
36
pression,
of stenosis.
between preoperative symptom duration and results of surgery, although
only 24 patients were evaluated.
of symptoms, the data are also not clear on how preoperative neurological
status affects surgical outcome. A meta-analysis by J. Anamasu et al suggests
that the larger, more recent studies indicate a positive association between
the presence of a proximal stenotic lesion,37 and a greater degree
38
Another study looking at OLF did not show an association
39
As with the importance of the duration
316
P A R T V I Other Surgical Treatment Modalities: Thoracic Spine
preoperative neurological function and surgical outcomes.40 Other studies
have highlighted some of the long-term complications of thoracic decompressive surgery, including the development of late kyphotic deformities and
spondylosis.
41,42
Treatment of thoracic stenosis due to disc herniation has poorer outcomes for those patients with advanced age, extended preoperative duration
of the condition, and greater degrees of myelopathy. Studies of patients with
nonligamentous causes of thoracic stenosis have questioned the long-term
prognosis following surgical decompression. Palumbo et al reviewed 12
patients with thoracic stenosis.
43
In 11 of the patients, stenosis was due to
spondylosis. Their results showed that 5 of 12 patients had initial improvement that later declined. They suggested that deterioration was due to
development of delayed stenosis, instability, or deformity.
CONCLUSIONS
Although thoracic spinal stenosis is a relatively rare condition as compared
to stenosis of the cervical or lumbar spine, the treating physician must consider it in the differential diagnosis of the older patient with thoracic back
pain or symptoms or signs of myelopathy. This awareness may prevent delay
in the diagnosis of this condition due to its similarity to the presentation of
lumbar stenosis. Most patients with a discogenic etiology for their pain can
be treated conservatively. Both CT and MRI aid in defining the pathology and determining the most appropriate treatment. CT myelography
should be avoided when possible in patients with OLF, as it can exacerbate
myelopathy. When surgery is indicated, the approach should be dictated
by the location of the disc. Patients with OLF or posterior longitudinal
ligament or neoplasm will most likely require both surgical decompression
and fusion.
Circumferential decompression carries a high risk of neurological deterioration. Patients with neurological complications due to metastatic lesions
in the thoracic spine benefit from surgical decompression in addition to
radiation. Larger, longer-term studies need to be performed to better define
the importance of preoperative duration of symptoms, neurological status,
and mode of decompression to overall prognosis. This task is made difficult
by the relative rarity of thoracic spinal stenosis.
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5 26 (2001) 558–566.
Stereotactic Radiosurgery
for Spine Tumors
Carmina F. Angeles, Robert E. Lieberson, and Jon Park
49
k e y p o i n t s
e CyberKnife system is a frameless stereotactic radiosurgery (SRS)
instrument that consists of a six megavolt linear accelerator (LINAC)
mounted on an industrial robot, a repositionable treatment couch,
orthogonally placed digital x-ray cameras, and a computerized targeting
system, used to treat spine tumors.
e overall accuracy of image-guided spinal SRS is ± 0.5 to 1.0 mm.
Lesions amenable to spinal SRS mainly include metastatic tumors,
intradural extramedullary tumors, select intramedullary tumors, and vascular
malformations.
Spinal instability and severe or progressive neurological deficits from mass
effect are contraindications for SRS unless decompression and stabilization
have been performed first.
Radiation-induced myelopathy is the most feared complication of SRS, but
is uncommon.
INTRODUCTION
Stereotactic radiosurgery (SRS) for the spine is a noninvasive technique that
accurately delivers large doses of radiation to small targets, through the use
of numerous highly collimated cross-fired beams. Spinal SRS has proved
effective in treating most metastases, many benign intradural tumors, some
intramedullary tumors, and compact intramedullary arteriovenous malformations. It can be used for the older patient or in patients with widely metastatic disease, when open surgery might be contraindicated.
Radiosurgery was developed in 1949 by Lars Leksell and Bjorn Larsson at the Karolinska Institute in Stockholm. Their first system used orthovoltage x-rays, and a subsequent variant used a proton beam generated by a
cyclotron. Leksell’s Gamma Knife was introduced in 1967, as a lower cost
and more efficient system. Gamma Knife treatments provided a steeper dose
gradient outside the target region. Embedded in a cast-iron enclosure, the
device contained 201 radioactive cobalt sources focused at a single point or
isocenter. During treatment, the patient’s head was secured to a rigid frame
with pins and then inserted into the cast-iron device with the lesion positioned at the isocenter. In the mid-1980s, to make radiosurgery more accessible and less costly, Betti and Colombo modified conventional radiotherapy
linear accelerator-based (LINAC) systems to deliver frame-based radiosurgery. Although both the Gamma Knife and LINAC systems were powerful
tools for intracranial disease, they could not be easily adapted for extracranial
cases, primarily because of the necessity for frame-based target localization.
In 1991, the frameless CyberKnife system was developed by Adler at
Stanford University. From its inception, this device was intended to treat
both cranial and extracranial lesions with sub-millimeter accuracy. Since the
installation of the first clinical unit in 1994, over 8000 spinal lesions have
been treated at more than 180 worldwide CyberKnife sites. As in cranial
radiosurgery, spinal SRS delivers large but precise doses of radiation to a
target while sparing adjacent healthy tissues. In comparison, conventional
radiotherapy doses are limited by the sensitivity of the spinal cord.
RADIOSURGERY
Ionizing radiation damages DNA, protein, and lipids by creating free radicals
and causing either mitotic or apoptotic cell death. Larger doses, while more
effective in killing neoplastic tissues, endanger normal structures. Conventional radiotherapy, which uses small numbers of broad and relatively inaccurate beams, addresses the problem by dividing the dose over many daily
treatments. In contrast, SRS instruments can deliver scores of small, precisely
collimated beams. As a consequence, large radiation doses can be directed at
irregularly shaped lesions while avoiding adjacent radiosensitive tissue. The
target’s location and shape are delineated using computed tomography (CT)
or magnetic resonance (MR) images, and processed using dedicated treatment-planning software. Current radiosurgery systems capable of treating
spinal lesions include the CyberKnife, the Tomoscan (a CT-like device) and
various modified linear accelerators (LINACs). The Gamma Knife is currently able to treat only select upper cervical lesions.
The CyberKnife system is a completely frameless, image-guided, robotic
radiosurgery system which consists, in part, of a lightweight, six megavolt
Clinical Case Examples
CASE 1
MC, a 66-year-old woman with medical contraindications to open surgery,
was treated with SRS for a spinal schwannoma. She initially presented
with a chronic cough and generalized weakness. Routine laboratory studies
showed pancytopenia, and flow cytometry was consistent with acute lymphocytic leukemia. e diagnosis was confirmed by bone marrow biopsy.
While undergoing chemotherapy in December 2008, she developed lower
back pain with subjective right leg weakness. A 10-by 7-mm epidural lesion,
compressing the S1 nerve root, was seen on MRI (Figure 49-1). A CTguided biopsy was consistent with schwannoma, but definitive treatment
was postponed because of her leukemia. By July 2009, the pain became
intolerable. She had 4/5 gastrocnemius weakness, numbness in the S1 distribution, and loss of the ankle reflex. A repeat MRI confirmed an increase
in the size of the schwannoma. Open surgery remained high risk, so in September 2009, the patient underwent CyberKnife treatment. She received 16
Gray (Gy) in a single session. Pain complaints improved, and all examination findings resolved over 2 months.
317
318
P A R T V I Other Surgical Treatment Modalitites: Thoracic Spine
F IG UR E 49 - 1 Gadolinium-enhanced T1-weighted axial image demon-
strating a 10- by 7-mm intradural extramedullary lesion compressing the S1 nerve
root. A CT-guided biopsy was consistent with schwannoma.
CASE 2
WF is a 68-year-old man with melanoma who received SRS treatment for
a recurrent spinal metastasis in a previously irradiated field. e patient was
initially seen with a melanoma of the back in 1999 and another of the neck
in 2003. Following local resections, he remained disease-free until March
2007, when, after complaining of low back pain, he was found to have a
4 × 3 cm lesion of the L3 vertebral body. ere was significant compression of the cauda equina due to epidural extension. A PET-CT showed
hypermetabolic areas in the lung, bone, and brain. He received conventional
F IG UR E 4 9 -2 Sagittal T1-weighted image with contrast, demonstrating enlarge-
ment of the previously treated L3 vertebral body metastasis with epidural extension causing
central canal stenosis.
radiotherapy of 37.5 Gy to the brain and 37.5 Gy to the lumbar spine. In
September 2009, the patient returned with increasing back pain, associated
with weakness. His strength was 4/5 in the right leg but his sensation was
intact. A follow-up PET-CT and MRI showed multiple new lesions and
enlargement of the previously treated L3 mass (Figure 49-2). Additional
conventional radiotherapy was not an option and a surgical decompression
was contraindicated based on his other medical problems. e L3 lesion
was treated with CyberKnife SRS, 24 Gy in three sessions. His symptoms
improved.
C H A P T E R 4 9 Stereotactic Radiosurgery for Spine Tumors
319
C
A
B
D
F IG UR E 4 9- 3 CyberKnife frameless stereotactic radiosurgery suite. A
modified 6-MV X-band LINAC designed specifically for radiosurgery is mounted
on a highlymaneuverable robotic manipulator (KUKA Roboter GmbH, Augsburg, Germany) (A). Two high-resolution x-ray cameras are mounted orthogonally to the headrest (B). One of the two x-ray sources is mounted in the ceiling
projecting onto the camera (C). The treatment couch is mobile, allowing the
x-ray sources to image targets at any point along the neuraxis (D).
linear accelerator attached to an industrial robot (Figure 49-3). The robotic
arm is unconstrained, using six degrees of freedom to deliver beams to virtually any part of the body from a wide range of angles. During treatment,
real-time orthogonal images of the patient are obtained frequently, enabling
the system to identify and automatically correct for small changes in patient
position.
Several conventional radiation therapy systems have been modified to
provide spinal SRS. The BrainLab Novalis and TX systems both use floorand ceiling-mounted x-ray cameras to verify patient position during therapy.
In contrast, the Varian Trilogy and Elektra Synergy systems utilize conebeam CT scanners mounted on the gantry of the LINAC. The cone CT
scanners acquire images before treatment, but do not do so regularly during
each session, and cannot always accommodate for changes in patient movement during therapy.
INDICATIONS FOR SPINAL RADIOSURGERY
Indications for spinal SRS continue to evolve (Tables 49-1 and 49-2).
The most commonly treated spinal lesions are metastatic (Table 49-3).
A biopsy may not be necessary prior to treatment if the diagnosis is clear
from the clinical history and imaging. Ideally, lesions should be less than
5 cm in maximal diameter, well demarcated, and clearly seen on CT and/
or MRI. For most tumors, local control rates are equivalent or superior
to conventional radiation and complications are generally lower than
with open surgery. In some particular cases, spinal SRS may be useful for
ablating the more radioresistant tumors.
irradiated patients where the adjacent spinal cord has already received
the maximum tolerated radiation dosage, the efficacy of spinal radiosurgery may be compromised because of the need to lower the radiosurgical
dose.
Spinal SRS is contraindicated in several situations. When there is significant cord or nerve root compression resulting in severe or progressive
neurological deficits, surgery may yield the best outcome. This is especially
true for bony or benign lesions, which involute slowly following treatment.
In the presence of spinal instability, SRS should only be performed as an
adjuvant therapy after decompression and stabilization or vertebroplasty
has been performed first. In cases in which there is no known systemic
disease and pathology cannot be reasonably ascertained by radiographic
studies, radiosurgery is contraindicated without first establishing a diagnosis. Some large tumors are best treated with a debulking procedure followed by SRS.
1
However, in those previously
TA BL E 49 -1 In dications for Spina l SRS
Tumors that are highly radiosensitive.
Post-resection cavity
Post-radiation therapy local irradiation
Recurrent disease post surgery and/or irradiation
Inoperable lesion
High-risk location of lesion
Slowly progressive but minimal neurological deficits
Patient with medical comorbidities that preclude surgery
Patient declines surgery.
TA BL E 49 -2 Contr aind icat ions for S pina l SRS
Spinal instability
Neurological deficit due to physical spinal cord or nerve root compression
Adjacent cord previously irradiated to the maximum dosage
Generalized metastatic involvement of the axial skeleton
Epidural carcinomatosis
TA BL E 49 -3 Le sion s Treata ble with Cybe rKni fe
Radi osur gery
Tumors
Benign
Neurofibroma, schwannoma, meningioma, hemangioblastoma, chordoma,
paraganglioma, ependymoma, epidermoid
Malignant/metastatic
Breast, renal, non-small cell lung, colon, gastric and prostate metastases;
squamous cell (laryngeal, esophageal, and lung) tumors; osteosarcoma;
carcinoid; multiple myeloma; clear cell carcinoma; adenoid cystic carcinoma;
malignant nerve sheath tumor; endometrial carcinoma; malignant neuroendocrine tumor
Vascular Malformations
Arteriovenous malformation (types 2 and 3)
TREATMENT DETAILS
Image-guided systems do not require rigid immobilization or invasive
frames. Instead, noninvasive custom masks or cradles are made for each
patient and used during image acquisition and radiosurgery. These devices
improve comfort, expedite alignment, and limit movement. For upper cervical lesions, a thermoplastic mask is made for each patient (Aquaplast, WFR
Corp., Wyckoff, NJ; Figure 49-4A). For thoracic and lumbar lesions a custom vacuum-molded body cradle is used (AlphaCradle, Smithers Medical Products, Inc., Akron, OH; Figure 49-4B). For some cervicothoracic
lesions, both devices are utilized.
Bony landmarks of the spine are used to target cervical, thoracic,
and lumbar lesions, as well as some pelvic lesions, scapular and rib head
masses, and paravertebral soft tissue tumors. The presence of spinal stabilization hardware does not interfere with target localization. Digitallyreconstructed radiographs (DRRs) are created as part of the treatment
plan and are used to establish the relationship of the target to regional
bony landmarks. The accuracy of CyberKnife using bony landmarks
approaches ±0.5 mm
2
.
320
Synthetic image A
P A R T V I Other Surgical Treatment Modalitites: Thoracic Spine
A
F IG UR E 4 9 -4 The Aquaplast mask is used as an immobilization device in cervical spine patients during CyberKnife treatment (A). AlphaCradle custom body
mold is used in thoracic, lumbar, and sacral lesions during CyberKnife treatment (B).
Camera image A Overlay of images A
Synthetic image B Camera image B Overlay of images B
B
F IG UR E 4 9 -5 Implanted gold seeds (fiducials). Left: CT-based DRRs from the perspective of the two orthogonal CyberKnife mounted x-ray cameras (A and
B). Center: Real time x-ray images from the two x-ray cameras. Right: Superimposed DRRs and actual radiographic images.
C H A P T E R 4 9 Stereotactic Radiosurgery for Spine Tumors
321
F IG UR E 4 9- 6 Fine-cut CT is used in delineating the lesion to be treated. Contour of L3 metastasis in axial, sagittal, and coronal projections is drawn. The
epidural metastasis is in red.
For lesions not associated with bony landmarks, or where there is severe
osteoporosis, localization may be based on implanted fiducials. Stainless steel screws in adjacent bone, or “gold seeds” adjacent to or within the
lesion, can be inserted prior to imaging (Figure 49-5). A minimum of three
clearly visible, non-collinear fiducials is needed. Ideally, they are placed in
bone or firm tissue, surround the target lesion, and do not overlap in 45°
oblique images. Prior to treatment delivery, the tumor location relative to
the implants or bony landmarks is established based on DRRs. The accuracy using implanted fiducials may be lower than with bony landmarks and
depends on the number and location of the implants.
2
Most patients are imaged and treated supine. Treatment planning begins
with a fine cut CT scan, (1.25-mm slices). The CT has the special resolution of available technologies and is required to delineate the lesion (Figure
Physical parameters are adjusted and refined iteratively until an optimal
plan is obtained. Ideally, the beams are evenly distributed over the surface
of the target, the target receives at least the prescribed dose, and the dose to
adjacent structures is minimized.
Spinal SRS is an outpatient procedure. At the time of treatment,
patients are positioned so that the lesion is near the center of an imaginary
80 cm diameter sphere. Orthogonal images are obtained by the digital x-ray
cameras and compared with precalculated DRRs. The couch position is
adjusted and the location of the target is confirmed. The robotic arm then
moves the LINAC to each of the individual beam positions, and each beam’s
dose is delivered. During treatment, images are repeated frequently and the
couch position is adjusted to preserve accuracy. The process is automatic,
but is monitored closely by a radiation therapist.
49-6) and create the DRRs used for localization (Figure 49-7). MRIs, posi-
tron emission tomography (PET) scans, or three-dimensional (3-D) angiograms are commonly used in addition. Treatment plans for CyberKnife are
designed using the Accuray Multiplan System (Figure 49-8). The various
stereotactic image sets needed for target definition are transferred to the
planning computer and aligned to one another using a semi-automatic process. Utilizing a graphic interface, the surgeon outlines the target lesion and
adjacent radiation-sensitive structures, such as the spinal cord, esophagus,
or kidneys, creating a 3-D representation of relevant anatomy (Figure 49-9).
A dose and treatment schedule is specified by the surgeon and the radiation oncologist. A radiation physicist computes treatment plans, seeking an
optimal dose conformation and a corresponding array of treatment beams.
TREATMENT OF SPINAL METASTASES
In older populations, the majority of spinal tumors are metastatic (see Case
2). Forty percent of cancer patients develop at least one spinal metastasis.
SRS is perhaps the least invasive of available treatments, and can deliver
much higher doses than conventional radiotherapy while limiting cord exposure. SRS generally takes 1 to 3 days, while conventional radiotherapy may
require 4 to 6 weeks. Multiple lesions can be treated safely and, because of
the shorter treatment schedules, the treatment of asynchronous metastases
is more convenient. SRS is appropriate as an adjuvant following a debulking
procedure or in conjunction with a stabilization procedure such as fusion or
322
P A R T V I Other Surgical Treatment Modalitites: Thoracic Spine
F IG UR E 4 9 -7 Contour of L3 metastasis and spinal roots with superimposed isodose lines from the treatment plan, in axial, sagittal, and coronal projections.
The epidural metastasis is in red, the spinal roots are blue, and the 80% isodose line is the smaller green line.
vertebroplasty. SRS can be a good treatment modality for those with limited
life expectancies, or those undergoing other concurrent treatments. Spinal
radiosurgery can be highly effective in controlling pain, such as in Case 1,
with up to 100% of patients reporting relief in some series.
3
Debate continues regarding the most appropriate treatment margins.
Some centers radiate only tumor seen on MRI, while others recommend
treating the entire affected vertebral body including pedicles. Up to 18% of
local failures are due to recurrences in the pedicles.
4
Amdur et al5 advocate treating visible tumor plus a 1-cm margin in bone or a 2-mm volume
beyond the cortex. We typically treat only the volume of tumor seen on
CT or MRI. There are no studies that clearly demonstrate a benefit of one
approach over the other. Dose recommendations are variable, with single
session prescriptions ranging from 8 to 24 Gy in the published literature.
We use 16 to 25 Gy in one to three fractions, depending on tumor type.
Local control is achieved in 77% to 100% of cases, and control rates are
histology have been shown to respond well to SRS. SRS for these benign
spinal lesions is appropriate for inaccessible tumors, syndromic lesions that
are multiple, for patients with significant medical comorbidities, or for those
who decline open surgery. In older patients, the risks associated with open
surgery are greater, so SRS may be appropriate for most intradural extramedullary lesions in this population.
In our institution, we have treated 110 patients with 117 lesions
(unpublished data). Fifty-six percent of schwannomas (see Case 1) and
meningiomas have stabilized after SRS and 44% have regressed radiographically. Neurofibromas did less well, with 11% enlarging, and up to 80% of
patients reporting progressive neurological deficits. We have observed that
most myelopathies and radiculopathies improve after SRS treatment. Two
5
of our SRS-treated patients required open resection for tumor enlargement.
Three needed surgery for persistent or progressing symptoms. One patient
developed a radiation-induced myelopathy.
independent of histopathology (Table 49-4).
TREATMENT OF INTRAMEDULLARY LESIONS
TREATMENT OF INTRADURAL EXTRAMEDULLARY LESIONS
Most intradural extramedullary lesions are benign. Surgical resection is
most commonly recommended since it provides immediate decompression,
yields a tissue diagnosis, and is usually curative. Intracranial lesions of similar
Sixteen of the 92 hemangioblastomas treated in our institution were spinal intramedullary tumors. These were treated with a median radiosurgical dose of 23 Gy. After a median follow-up of 34 months, 15 of the 16
spinal hemangioblastomas either decreased or remained the same in size.
Intramedullary hemangioblastomas associated with significant edema or
6
C H A P T E R 4 9 Stereotactic Radiosurgery for Spine Tumors
323
F IG UR E 4 9- 8 Treatment plan for L3 metastasis is designed using the Accuray Multiplan System.
cysts might do less well, based on our experience with similar intracranial
lesions.
Although the data for ependymomas are limited, a few published stud-
ies have shown SRS to be efficacious.
7
We know less about SRS for spinal
astrocytomas, but for those which are well circumscribed, spinal SRS may
be an appropriate alternative to surgery.
Intramedullary spinal cord metastases are rarely seen. They constitute
only 8.5% of central nervous system metastases,
likely increase with longer patient survival and as the population ages.
Wowra et al
9
reported that 96% of spinal metastases were well controlled
8
but their frequency will
with spinal SRS and that the risk of radiation myelopathy was less than 1%.
COMPLICATIONS
SRS treatment failures can be categorized as “in-field failures” and “marginal
failures.” “In-field failures” involve tumor regrowth within the treated volume and may be related to inadequate dosing. “Marginal failures” involve
regrowth at the edges of the treated volume and may be related to poor
imaging, an underestimation of the tumor volume, or inaccuracies in the
position or set-up. “Distant failures,” which involve new lesions in untreated
portions of the spine, occur in 5% of patients, and are due to the underlying
disease and not to a failure of technique.
Neurological complications of SRS are categorized by their time
of onset. Acute complications occur within a month and are usually
transient. They are related to edema and can be treated with steroids.
Subacute complications occur 3 to 6 months after treatment and are
usually secondary to demyelination. The prognosis for recovery is good.
Radiation-induced myelopathy, the most feared side effect of SRS,
is a late effect, occurs after 6 months, and is usually irreversible. In
1000 patients treated with CyberKnife for spinal lesions, six developed
myelopathy (0.6%).
10
To prevent radiation-induced myelopathy, we avoid
exposing more than one cubic centimeter of spinal cord to more than
8Gy in single session plans.
Other less severe side effects of spinal SRS include local skin reactions, which are occasionally seen when the posterior elements are treated,
and gastrointestinal complaints such as nausea, pharyngitis, esophagitis, or diarrhea. Renal complications are rare even after thoracolumbar
treatments.
CONCLUSION
The successes of intracranial radiosurgery inspired the development of spinal SRS. Many spinal lesions may not be amenable to complete surgical
resection. SRS is both safe and effective treatment for metastatic lesions of
the spine and for some intradural extramedullary tumors. Early results in
treating intramedullary lesions are encouraging. Spinal SRS, a completely
noninvasive treatment, is particularly suited for older patients and those
with significant concomitant medical problems.
324
P A R T V I Other Surgical Treatment Modalitites: Thoracic Spine
F IG UR E 4 9 -9 Outlines of the target lesion and adjacent radiation-sensitive structures, such as the spinal nerves and kidneys, with dose lines as specified by
the surgeon and the radiation oncologist.
TA BL E 49 -4 SRS for Spinal Vert ebral Metastas es
Site
Amdur, et al., 2009
Wowra, et al., 2009
Yamada, et al., 2008
Gibbs, et al., 2007
Chang, et al., 2007
Ryu, et al., 2007
Gerszten, et al.,
17
2005
Milker-Zabel,
18
2003
16
et al.,
Lesions /
Patients
11
25 / 21 Various LINAC / IMRT 15 Gy / 1 Lesion with
15
134 / 102 Various CyberKnife 15 to 24
14
103 / 93 Various LINAC / IMRT 18 to 24
6
102 / 74 Various CyberKnife 14 to 25 Gy /
7
74 / 63 Various LINAC / IMRT 27 to 30 Gy /
230 / 177 Various LINAC / IMRT 8 to 18
68 / 50 Breast CyberKnife 12.5 to 22.5
19 / 18 Various LINAC / IMRT
Tumor
Type Modality
or FCRT
Dose /
Fractions Contouring Complications
No neurological
margin
toxicity
Not specified No SRS-related
Gy/ 1
neurological
deficits
Gy/ 1
Entire vertebral body
No neurological
toxicity
Lesion only ree cases
1 to 5
3 to 5
Gy / 1
Gy / 1
24 to 45 /
variable
Entire vertebral body
Entire body
with pedicles
Entire vertebral body
Entire vertebral body
myelopathy
No neurological
toxicity
1% risk of
myelopathy
No neurological
toxicity
No neurological
toxicity
Pain
Reduced
Local
Control
Overall
Survival
43% 95% 25% at
1 year
86% 88% Median
survival
1.4 years
Not
reported
84% No symptom
90% 36% at
3 years
46% at
progression
1 year
60% 77% 70% at
1 year
85% 96% 49% at
1 year
96% 100% Not
reported
81% 95% 65% at
1 year