Brain Tumors: Primary - Radiotherapy

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Advanced imaging techniques are now allowing frameless stereotaxy, which eliminates the frame and may be effective on more tumors. For example, high-field interventional MR imaging (iMRI) uses a guidance system based on cruise-missile technology to calculate the slightest variations in movements of the head and the location of the tumor relative to these movements. These calculations are then used to target the radiation beams directly on the tumor, even if the patient's head is moving slightly.

Delivery of Radiation Beams. Once the preliminary planning stage has been completed, treatment begins. Several advanced machines, such as the gamma knife, adapted linear accelerator (LINAC), and cyclotron, are being used with stereotaxy and can deliver very focused beams of radiation. Actual treatment takes 10 minutes to 1 hour.

• The gamma knife uses gamma rays that are sent from multiple points to converge at a single point on the tumor. Although each gamma-ray beam is very low dosage, when the beams converge, the intensity and destructive power is very high. The gamma knife is limited to very small tumors and so is generally useful as a booster after standard radiation, surgery, chemotherapy, or combinations.
• The linear accelerator (LINAC) produces photons (positively-charged atomic particles) in patterns that are matched to the tumor shape. The patient is positioned on a bed that can be moved to allow flexible positioning. It allows treatment over multiple sessions of small doses (fractionated stereotactic radiotherapy), instead of a single session. This means that larger tumors can be treated.
• The cyclotron is basically an atom smasher, which produces protons that can be directed toward the tumor. As part of this procedure, some researchers are using boron neutron capture therapy (BNCT). BNCT employs intravenous administration of a boron compound, which is picked up more selectively by tumor cells than by normal brain tissue. The cyclotron delivers a single dose of radiation that triggers the release of high-energy particles from the boron to destroy nearby tumor cells. The cyclotron is available only in a very few locations, and there have been few trials to date.