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Cummings Ch 179
Stereotactic Radiation Treatment of
Benign Tumors of the Cranial Base
Sophie Shay, MD
February 5, 2014
Department of Head and Neck Surgery
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Key Points
• Stereotactic radiation therapy demonstrates good shortterm control for many benign cranial base tumors
• Short-term quality of life outcomes favor stereotactic
radiation therapy over conventional surgical
management
• Radiation-induced cranial nerve injury has been
reduced as lower doses of radiation have come into use
• Long-term control and radiation-induced malignancy
risk will be known in the next decade with further study
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Overview/Principles
• Goal = growth arrest of benign tumors
• Introduced in 1967 by Lars Leksell – early complications
including brainstem radiation damage, hydrocephalus,
cranial neuropathies
• Definition: application of any kind of ionizing radiation in
a precise dosing mechanism to a target while limiting
radiation exposure and damage to the adjacent
surrounding tissues
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From Pasha’s small paragraph on this topic…
• Good treatment option for elderly patients
• Avoid
radiation in children, tumors with undocumented growth,
or tumor prone (ie – NF-2) patients
• Consider for tumors < 2.5 cm
• Risk
of CNVII and CNVIII injury may be less than surgical
excision for small tumors
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Basics of delivery
• Gamma Knife
• Linear Accelerators (LINACs)
• Single dose vs fractionated
• Ionizing radiation  excites
electrions  free radical
change  DNA damage 
Apoptosis
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Outcomes and Complications
• Tumor CONTROL: No growth of tumor vs. tumors that
required no further treatment
• 1-2% of vestibular schwannomas resolve completely,
tumor control is achieved in 74-100%
• Hearing loss
• Over
6-24 months, with an average decline of 15-20 dB
• Hearing
loss also related to initial tumor size
• Facial nerve injury – rare and usually transient
• Trigeminal nerve toxicity – mild hypesthesia to
trigeminal neuralgia
• Hydrocephalus
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Types of Tumors Treated
• Vestibular Schwannomas/Acoustic Neuroma
• NF-2 related Vestibular Schwannomas
• Also
effective at tumor control
• University
of Pittsburgh – tumor volume is a predictor of tumor
control
• 0.01-0.3%
malignant transformation
• Cystic Schwannomas
• More
controversial, can enlarge s/p radiation surgery
• Jugular Foramen Schwannomas (CN IX, X, XI, XII)
• Paraganglioma (CN VII, VIII)
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COCLIA Questions
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QUESTION 1:
Describe the risks and benefits
of using either stereotactic
radiosurgery or skull base
resection of vestibular
schwannomas
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SRS vs Surgery for Vestibular Schwannomas
• SRS
• Benefits
• Decreased
• Faster
immediate morbidity to CNVII, CNVIII
recovery, lower cost
• Risks
• Malignant
• Requires
• Risk
transformation
long term surveillance
of treatment failure (particularly for large tumors)
• Higher
incidence of CNV injury
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SRS vs Surgery for Vestibular Schwannomas
Surgical approaches to CPA
• Translabyrinthine
• (+)
direct route, excellent
exposure, less risk of CNVII
injury
• (-)
sacrifices hearing, higher
risk of CSF leak
• Retrosigmoid/Suboccipital
(large tumors)
• (+)
wide exposure, hearing
preservation
• (-)
Limited exposure to IAC,
higher risk of CNVII injury
• Middle Cranial Fossa (Small
IAC lesions)
• (+)
Hearing preservation
• (-)
Retraction of temporal
lobe, higher risk of CNVII
injury
• Retrolabyrinthine (not for VS)
• (+)
preserves hearing,
shorter operative time
• (-)
limited exposure (cannot
access IAC or porus
acousticus)
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QUESTION 2:
What are the long-term control
rates for vestibular
schwannoma using stereotactic
radiosurgery?
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VS Control Rates
• 1-2% of vestibular schwannomas resolve completely
• 74-100% tumor control over varied durations of follow
up
• 5-year progression-free tumor control = 95% for single
dose SRS and 94% for fractionated regimens
• Data is limited
• Literature
is limited to retrospective studies
• Tumor
Control is not well defined (ranging from no radiographic
enlargement over a set parameter to failures requiring surgical
treatment)
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SRS: definitions and applications
• Application of any kind of ionizing radiation in a precise
dosing mechanism to a target while limiting radiation
exposure and damage to the adjacent surrounding
tissues
• Applications: Vestibular schwannomas/Acoustic
neuromas, Paragangliomas, Jugular Foramen
Schwannomas
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QUESTION 4:
What are some absolute and
relative contraindications to
radiation therapy?
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Contraindications to radiation
• Absolute contraindication
• Gorlin’s
Syndrome (proliferation of BCC)
• Relative contraindication
• Previous
• Inability
head and neck radiation
to make appointments
tissue disorders (i.e. – SLE, scleroderma) with
significant vasculitis
• Connective
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QUESTION 5:
What are the complications of
primary radiation therapy?
What are the acute and late
effects of radiation therapy?
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Complications of radiation
• Acute: during the course of radiation
• Mucositis,
odynophagia, dysphagia, hoarseness, xerostomia,
dermatitis, weight loss, alopecia
• Late: occurring after the completion of treatment
• Xerostomia,
osteoradionecrosis, fibrosis in normal tissues,
thyroid dysfunction, vascular complications (i.e.- carotid artery
rupture, pseudoaneurysm), fistula formation, neurologic
complications (Myelopathy – paresis, numbness, sphincter
dysfunction), radiation-induced cancer, otologic sequelae,
cataracts, nonfunction larynx, stricture/stenosis
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QUESTION 6:
What are the effects of
radiation on a
cellular/molecular level?
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Radiobiology
• Rad=Radiation Absorbed Dose
•1
Gy = 100 Rads, 1cGy=1 Rad
• Cells are considered “killed” when they lose clonogenic
survival
• Direct damage to DNA, cell membranes
• Indirect damage (secondary damage) – DNA injury from
production of free radicals, cell death
• Larger tumors have a more hypoxic center = less
sensitive to radiation (fewer free radicals)
• Cell death occurs with proliferation – rapidly growing
tumors are more susceptible to RT
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QUESTION 7:
Discuss the 4 "Rs" of radiation
therapy:
Reassortment/Redistribution,
Repair, Regeneration, and
Reoxygenation.
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4 “R’s” Of Radiation Biology = Fractionation
• Reassortment/Redistribution
• Fractionation
allows for cells to proceed in their cycle to more
radiosensitive stages of their cell cycle (mitosis, late G1, early Sphases)
• Reoxygenation
• Fractionation
allows for reoxygenation of previously more
hypoxic cells (making them more susceptible to RT)  more
free radical generation
• Repopulation/Regeneration
• Prolonged
waiting between fractions results in regrowth of tumor
cells from sublethal damage
• Repair
• Normal
tissue tends to have better repair than tumor cells, and
therefore recovers more quickly
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QUESTION 8:
Name all those holes in the
base of the skull and tell us
what goes through each.
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QUESTION 9:
Review the boundaries of
anterior, middle and posterior
cranial fossa.
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Anterior cranial fossa
• Anterior anterior border = posterior wall of the frontal
sinus
• Posterior border = the anterior clinoid processes and
the planum sphenoidale, which forms the roof of the
sphenoid sinus.
• Lateral border = the frontal bone forms the lateral
boundaries. The frontal bone houses the supraorbital
foramina, which, along with the frontal sinuses, form 2
important surgical landmarks during approaches
involving the anterior skull base.
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Middle cranial fossa
• Anterior border = the greater wing of the sphenoid
• Posterior border = clivus
• Lateral border = the greater wing of the sphenoid forms
the lateral limit as it extends laterally and upward from
the sphenoid body to meet the squamous portion of the
temporal bone and the anteroinferior portion of the
parietal bone.
• Floor = The greater wing of the sphenoid forms the
anterior floor of the fossa. The anterior aspect of the
petrous temporal bone forms the posterior floor of the
middle cranial fossa.
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Posterior cranial fossa
• Anterior border = the apex of the petrous temporal. The
petrous portion of the temporal bone and the greater
wings of the sphenoid bone are particularly important
for identifying structures.
• Posterior border = the occipital bone, with contributions
from the sphenoid and temporal bones.
• Lateral border = the posterior surface of the petrous
temporal bone and the lateral aspect of the occipital
bone
• The overlying tentorium cerebelli separates the
cerebellum from the cerebral hemispheres above
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QUESTION 10:
Discuss the classification of
glomus tumors (Fisch vs.
Glasscock)
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Pasha Table 8-4
• Glasscock-Jackson Classification
• Glomus Tympanicum
I.small mass limited to the promontory
II.Tumor filling the middle ear space
III.Tumor extending into the mastoid
IV.Tumor extending into the mastoid, EAC, and anterior
to the carotid artery
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• Glomus Jugulare
I.Small tumor involving jugular bulb, middle ear, and
mastoid
II.Tumor extending under IAC with or without intracranial
extension
III.Tumor extending into petrous apex with or without
intracranial extension
IV.Tumor extending into the clivus, infratemporal fossa,
may have intracranial extension
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Fisch Classification
A. Tumor involves middle ear only (glomus tympanicum)
B. Tumor involves middle ear and mastoid
C. Tumor extend in the infralabyrinthine region toward
petrous apex
D. Tumors with < 2 cm intracranial extension (D1) or
>2cm (D2)
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