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Tomotherapy
The field of radiation oncology changes rapidly as new
and better methods of treatment are found. Many of these changes are the
result of enhanced computer applications and their integration into diagnostic
imaging and dose delivery equipment. The newest concept in this regard
is called helical tomotherapy, which allows the radiation oncologist to
deliver radiation therapy to the patient with
surgical precision. This translates into more effective treatment of the
mesothelioma tumor while sparing healthy tissue and significantly reducing
side effects.
Basically a combination of spiral CT scanning and Intensity Modulated
Radiation Therapy (IMRT), this state-of-the-art technology is now being
used at a growing number of facilities nationwide. Following is a brief
description of steps in the helical tomotherapy process.
- 3-D imaging is generally performed with standard CT imaging equipment.
- The radiation oncologist uses special software to establish the contours for each target volume and identifies organs or structures at risk. The doctor then decides what dose the target area(s) should receive as well as what dose(s) will be acceptable to the organs or structures at risk.
- The 3-D data and the contours of the target volume and organs or structures at risk are transferred to the tomotherapy treatment planning computer which performs delivery optimization calculations including leaf positions for the gantry angles and couch positions for the patient.
- Computer planning data is transferred to the tomotherapy unit for delivery implementation.
- A CT scan is taken just prior to treatment to verify the anatomical targets and patient position. This affords the opportunity to make any necessary adjustments and ensure correct dose delivery.
- After verification of the above, the dose is delivered to the patient. The radiation is produced by a linear accelerator (linac) which travels in circles around the gantry ring. The linac moves in unison with a multileaf collimator (MLC). The leaves of the collimator move in and out rapidly to modulate the radiation beam leaving the accelerator. Concurrently, the patient couch is being guided slowly through the center of the gantry ring. Each time the accelerator circles, the radiation beam is directed at a slightly different plane.
- While treatment is in progress, the amount of actual radiation to the patient is measured so that dose delivery can be verified and compared to the planned dose. If necessary, adjustments can be made for subsequent treatments.
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