Image-guided radiation therapy (IGRT) is a precise technique for delivering radiation beams to a tumor so that more of the dose is delivered to cancer cells and less goes to healthy organs and tissue around the tumor. In IGRT, a radiation oncologist uses precise imaging technology and a linear accelerator (LINAC) to deliver the radiation. The imaging allows the oncologist to see the tumor before, during and after treating it.
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At the start of each therapy session for lung cancer or mesothelioma, the patient is placed on the treatment table so that the marks on the skin outlining the treatment area are in alignment with the path of the radiation beam. Images are taken, which are compared through the use of computer software to the preliminary images that were taken when the course of the patient’s therapy was being planned.
A comparison of images indicates whether adjustments need to be made to the patient’s position and/or to the path of the radiation beams. If adjustments are needed, a new set of images can be compared to the earlier set to ensure the tumor is being accurately targeted.
Approximately 25 to 30 percent of non-small cell lung cancer (NSCLC) patients are diagnosed in an early stage, meaning their tumors are confined to the functional part of a single lobe of one of the lungs. In these cases, the typical treatment is to remove the tumor surgically from the affected lobe. Non-small cell lung cancer accounts for about 80 percent of the lung cancer cases.
Some patients have pulmonary or cardiovascular disease, a complication that makes surgery a dangerous option – and not an option at all for some. When that is the case, an alternative treatment is needed. That alternative typically is radiation therapy.
When three-dimensional radiation therapy is used, the radiation oncologist can see both the tumor and the normal tissues surrounding it in three dimensions and that allows the physician to calculate radiation doses to the whole volume of tumor while preventing as much damage as possible to healthy parts of the lungs and organs/tissues near it.
NSCLC patients treated with image guided radiation therapy (IMRT) are placed in customized cradles when they are on the treatment table so that they remain immobilized. The necessity for keeping the patient motionless is to avoid shifting of the tumor position. The pattern of tumor motion during the natural respiratory cycle is tracked through a Dimensional Gated Planning CT that monitors the changes in tumor position and shape during the various phases of the breathing cycle.
A dose of 2 Gray or Gy is administered to the tumor daily over six to seven weeks so that the patient will ultimately receive a total dose of 60-70 Gy. A Gray is one unit of ionizing radiation dose that is absorbed by one kilogram of human tissue.
The older form of external beam radiation that only allowed for two-dimensional treatment planning showed a five-year survival rate of 20 to 30 percent. Advances in radiation treatment, including image-guided treatment improved lifespan for small-volume lung cancer patients. According to one study, the one-year survival rate at is 94 percent, and a two year rate is 73 percent.
Treatment centers use a number of different imaging systems and machines as a prelude to radiation therapy. All of these machines have their strengths, but the all have the same goal: to get the best images of tumors that everyone wants to shrink or eliminate. If you are a candidate for IGRT, you likely will get to know one or more of these types of equipment.
A computerized tomography scan, also known as a computerized axial tomography (CAT) scan uses multiple X-ray images that are combined by a computer to create images that are cross-sections and/or 3D.
This type of imaging process uses a magnetic field and radio waves to create 3D images able to be viewed from a variety of angles.
The patient is given a small amount of radioactive material either though injection, inhalation or orally. This material collects in a diseased area and is identified as a bright spot on the scan.
This is the same technology doctors use to monitor the progress of pregnancies. A small device, called a transducer, is passed along the area of the body to be tested. It produces sound waves that bounce off tissue and create echoes. The echoes are sent to a computer that uses them to form an image called a sonogram.
Increasing the radiation dose based on the tumor is balanced against the risk for damage to the unaffected lung, heart, esophagus and spinal cord. The type and severity of side effects depends on the total radiation dose, the dose the patient receives during each treatment session, and the volume of healthy tissue exposed to radiation.
Radiation can cause pneumonitis, an inflammation of the air sacs in the lung, or fibrosis, scarring of lung tissue. Both of these conditions result in the patient experiencing shortness of breath and a decrease in overall pulmonary function. If these conditions are severe enough, the patient may need oxygen treatment either temporarily or permanently.
Radiation injury to the esophagus, the tube that brings food from the mouth to the stomach, may cause painful swallowing and narrowing of the esophagus. This may result in the patient not eating properly and experiencing malnutrition.
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