the clinical indications.
Manual Implants
Manual implants usually employ low-activity (hence low dose rate) material and could be either
temporarily or permanently inserted into the body tissues or body cavity. The sources are usually much
smaller than the LDR caesium pellets and may be in the form of seeds, wire, hairpins or needles etc.
Special Procedures
Stereotactic Radiosurgery
Radiosurgery is a treatment technique to deliver sharply focused beams of radiation to intracranial
targets. Multiple small beams of radiation intersect at a focal point to create a small ball or sphere of
high dose radiation which then could be targeted with a high degree of precision to an intracranial lesion
using a head frame unit attached to the skull. The term "stereotactic" refers to the targeting mechanisms
which employ computerised tomography (CT), magnetic resonance imaging (MRI), or angiography to
direct the radiosurgery beams in 3D. Stereotactic therapy is used as both a single dose radiation
treatment, stereotactic radiosurgery (SRS), and multiple fraction of smaller doses called stereotactic
radiotherapy, (SRT).
There are currently two types of technology for the delivery of SRS: Gamma Knife, which employs an
array of over 200 concentrically positioned sources of cobalt-60 to aim at the intracranial target. Another
approach is to use a linear accelerator (with small treatment cone or miniature collimators) to create a
sphere of radiation by aiming an array of intersecting non-coplanar arc beams of radiation.
Malignant brain tumour, meningiomas, orbital tumours, arteriovenous malformations (AVM's), acoustic
neuromas, metastatic tumours to the brain, pituitary tumours and brain stem tumours, skull base
tumours, head and neck tumours including nasopharyngeal carcinoma and selected recurrent tumours
near the skull base are treated with these techniques.
Intensity Modulated Radiation Therapy
Intensity Modulated Radiation Therapy (IMRT) is a sophisticated technology that can deliver a high
dose of radiation to a tumour while sparing surrounding healthy normal tissues with good conformality.
The fundamental difference between conventional conformal radiation therapy and IMRT is beam
intensity; in conventional radiation therapy, the beam intensity is uniform, but in IMRT, the beam
intensity is varied across the treatment field. During IMRT treatment, when the tumour is the thickest,
the beam intensity is at its maximum, and when the tumour is the thinnest, the intensity is at its
minimum. This technique can also spare adjacent of overlying healthy tissues. Instead of the patient
being treated with a single, large uniform beam, the patient is treated with a large number of smaller
beamlets, each with different intensities or amounts of radiation.
IMRT allows the radiation oncologist to conform the radiation dose to difficult tumour volumes, yet
spare eloquent areas -- for instance, treating a tumour that has wrapped itself around the spinal cord.
IMRT is similar to conformal therapy, which is practiced in many radiation oncology centers, but
conformal therapy is limited to a geometric shaping of the beam with no intensity modulations across
the field.
When a tumour is not well separated geometrically from surrounding organs, adding modulation to the
geometric shaping of the beam is more effective in conforming the dose to a tumour while minimising
the dose to normal surrounding structures. This way, an optimised treatment plan can be created for a
given tumour of any size, shape or anatomical location.
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