Radiation Oncology—Stereotactic
Radiosurgery
Stereotactic radiosurgery
(SRS) is a technique for treatment of well defined lesions with a
high dose of ionizing radiation. This one-time outpatient treatment is
often an excellent alternative to complex surgical procedures requiring
lengthy hospitalization.
History
The concept of SRS was developed
in the 1950s by combining a neurosurgical localization frame with
multiple cross-firing beams of Cobalt-60 gamma rays. That technology
initially was utilized to create lesions a few millimeters in size deep in
the brain parenchyma for treatment of various neurologic conditions such
as Parkinsonís
disease, movement disorders or chronic pain. Ultimately it evolved
into the practice of oncology.
Linac Scalpel
Stereotactic radiosurgery
system installed at St. Agnes Cancer Center combines state-of-the-art
treatment planning tools with very precise localization and patient
positioning which provides unparalleled accuracy in the treatment
of intra-cranial lesions. Linac Scalpel technology
is capable to deliver SRS with either a conventional fixed cranial frame
or a frameless setup. Both systems utilize real-time infrared tracking feedback
and provide submillimeter accuracy. Additionally infrared emitting/reflecting
fiducial markers together with ultrasound probes give us the opportunity
to utilize SRS for extracranial targets as well.
Both the linear accelerator and the patient can be rotated
so that the beam of radiation is focused on a single point at all times.
The ability to rotate both the patient and the beam of radiation results
in spreading the dose around normal tissues and thus minimizes the damage
and complications.
TomoTherapy (Tomosurgery)
CT image guided Intensity Modulated Radiation Therapy system may
be preferable for highly irregular targets in the brain. Find out
more about TomoTherapy.
The development of non-invasive frameless image guided SRS has allowed
for treatment to be delivered in multiple fractions rather than single
session required by invasive head frames. Better understanding of radiobiology
of normal brain structures and utilization of conventional fractions of
radiation with Fractionated Stereotactic Radiation Therapy helps to spare
the optic and acoustic nerves and the brain stem as well.
Patient selection
Types of brain lesions that may be
appropriate for SRS:
- Benign brain tumors
- Acoustic neuromas
- Meningiomas
- Pituitary tumors
- Craniopharyngiomas
- Neoplasms of the pineal gland
- Trigeminal neuralgia
- Metastatic brain tumors
- Arteriovenous malformations (AVMs)
- Recurrent primary malignant brain
tumors
Stereotactic radiosurgery is often utilized in the management of brain
metastases. A recently reported multiinstitutional randomized trial showed
statistically significant survival benefit for selected patients with a
limited number of brain metastases who received SRS boost in addition to
whole brain radiation therapy.
Palliative efficacy of SRS is also well established in reirradiation of
patients who previously received whole brain RT and subsequently sustained
recurrence. On the other hand, utilization of SRS as solo modality even
for patients with single metastasis at the present time is considered investigational.
SRS at St Agnes Cancer Center
Consultation with a radiation
oncologist and neurosurgeon
MRI used for treatment planning usually is obtained on a separate
day and is not different from a routine gadolinium enhanced MRI.
- Frameless System
- Head immobilization
consists of typical radiation therapy face mask which is individually
made from thermoplastic material.
- Infrared tracking detectors
are mounted on a custom made “bite
block” similar to a mouth guard.
- Head Frame System
- Head frame is place under local anesthesia by the
neurosurgeon in the morning of the procedure day; CT scan with
intravenous dye is performed subsequently.
- Tomotherapy
- Radiation oncologists at St. Agnes Cancer
Center are utilizing this unique radiation therapy delivery
system in stereotactic radiosurgery for selected patients.
- Find
out more about TomoTherapy.
SRS planning and treatment is done with
meticulous quality assurance. Treatment delivery takes between
one-two hours and all members of the team are present during the
SRS session.
Immediately after SRS is
completed the head frame is removed (if utilized) pin sites typically
do not require dressing.
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