Stereotactic radiation therapy:
SBRT is a type of external beam radiation therapy. Stereo means 3-dimensional (3-D) and tactic means a carefully planned action. Stereotactic radiation therapy allows radiation beams to be given to a very specific area, with a large dose. The technique utilizes multiple beams which all converge upon a very small target, thus the area of convergence receives the full dose while the remaining tissues are minimally dosed. The characteristic of this treatment is the rapid fall-off of dose.
There are 2 ways to deliver stereotactic radiation therapy treatment.
- Stereotactic radiosurgery (SRS) delivers a single high dose of radiation to the tumour (called a single fraction). This treatment doesn’t involve surgery. An incision (cut) is not made and tissue is not surgically removed.
- Stereotactic radiotherapy (SRT) gives smaller doses of radiation over a number of treatment sessions (called multiple fractions), until the desired total dose is given.
Stereotactic radiosurgery requires specialized equipment and training. Stereotactic radiation therapy requires complex treatment planning using computers and high-energy radiation machines. A CT or MRI scan is used to find and map the exact area to be treated. This helps ensure that the surrounding normal tissue is spared from radiation.
When treating brain tumours, the head must be kept in the same position for each treatment. People receiving stereotactic radiation therapy to the brain wear a special head frame (stereotactic frame) during their treatment.
- When SRS is used, the head frame is attached to the skull. A neurosurgeon injects a local anesthetic just under the scalp to numb the area. Then the surgeon places special screws or pins into the skull. These screws (or pins) fix the head frame to the skull. The skull screws and head frame are removed after the treatment is finished.
- When SRT is used, a removable head frame or a special face mask keeps the head in position.
When treating areas outside of the brain, multiple custom molds are used to ensure that the body does not move during therapy. No invasive fixation is necessary or possible. The precision of treatment is to within 3mm.
There are three delivery technologies which give equivalent results. Gamma Knife can only be used for brain tumors and is particularly beneficial for the smallest tumors such as brain-stem lesions. Linear Accelerator delivery is versatile, quick and accurate for the majority of body parts, with patient comfort and quickest treatment time. Cyberknife is a computer controlled linear accelerator which uses non co-planar angles for treatment.