Radiation

How radiation is used to treat mesothelioma

Radiation works by using high–energy rays to kill cancer cells.  Radiation is not a cure; still, in the course of treating pleural mesothelioma, radiation is often employed in a variety of ways.  For the best result, radiation is aimed at the entire chest.  But doctors must use low doses so that the heart, lungs, esophagus and spinal cord are not injured.

In cases of pleural mesothelioma, radiation may be used after surgery to attempt to prevent the cancer from returning.  This type of radiation is called adjuvant therapy and has been shown to improve the survival rate for patients who have early–stage mesothelioma.  Where pleural mesothelioma is advanced, and surgery is not possible, some people are given a combination of radiation and chemotherapy in an effort to slow growth and control the spread of the cancer.  Radiation may also assist in reducing pain levels in those with advanced pleural mesothelioma. 

At times, radiation is administered to the area in which a patient has had a tissue biopsy, or the place where a chest tube was inserted to drain fluid from a pleural effusion.  The goal of this procedure is to prevent mesothelioma cells from growing in the scar tissue.  It is not known if this is an effective use for radiation, however, as the studies on the question have reached conflicting results. 

Radiation is not generally recommended in cases of peritoneal mesothelioma because it is thought to result in too many side effects.  Still, it may be used to reduce signs and symptoms caused by the disease. 

There are three primary sorts of radiation used to treat mesothelioma.  In addition to the traditional external beam radiation, doctors are now using two innovative radiation therapies to treat the disease: brachytherapy and intensity–modulated radiation therapy (IMRT).

Traditional External Beam Radiation

External beam radiation therapy (EBRT) is directed to the tumor by means of linear accelerators.  These devices create high–energy external radiation beams that travel through healthy tissue into the region where the tumor is located.  To administer the radiation precisely, computed tomography (CT) scans and PET scans are used to concentrate on the areas in which the tumor may reappear.  By planning carefully, the radiologist is able to target the tumor with the highest level of radiation that can be delivered safely and to minimize the corresponding exposure of healthy tissue to the radiation.

Innovative Radiation Therapies

Brachytherapy

Brachytherapy is a form of radiation therapy used by many physicians to try to kill cancer cells in the chest cavity that cannot be removed during surgery.  “Brachy” means short and brachytherapy refers to therapy applied at a short distance.  Other terms for brachytherapy include sealed source radiotherapy, internal radiotherapy, seed implantation radiotherapy and endocurietherapy. 

Brachytherapy works by placing a radiation source directly into the body, usually inside the cancerous tissue or near it.  The radiation source sends out ionizing radiation that kills the nearby cancer cells.  Because the ionizing radiation can travel just a very short distance, the radiation attacks only the cancer, and not healthy tissue.  Brachytherapy is often performed during the same operation in which the tumor is removed.  When this occurs, the procedure is called “Intraoperative Radiation Therapy” (IORT).  Surgeons must ensure that a patient,s time in surgery is not extended for too long, or complications may result from the delay.  The overall risks and benefits and risks of IORT are still being evaluated. 

Brachytherapy may be either temporary or permanent. With temporary brachytherapy, the radiation material is inserted in or near the cancerous tissue for a fixed period of time and then removed.  With permanent brachytherapy, radioactive seeds about the size of grains of rice are implanted in or near the cancer tissue.  The seeds are woven into a flexible absorbable mesh, which is then stitched into place inside the body.  The seed implant remains permanently and delivers radiation continuously to the cancer for about three months, with some residual radioactivity remaining for about a year.

Brachytherapy can be either high dose or low dose.  High dose rate brachytherapy is generally performed as an outpatient procedure and is usually the temporary form of brachytherapy.  Thin catheters are implanted into the tumor and connected to afterloader.  The afterloader pushes the radioactive seeds one at a time into the catheters.  A computer is used to ensure that the seeds are delivered at precisely the right time and place.  The administration of each dose takes a few minutes.  Patients customarily receive multiple HDR brachytherapy treatments over a period of one to several weeks.  When the series of treatment is complete, the catheters are removed.

Low dose rate brachytherapy may be of the permanent or temporary variety.  The treatment is performed on an inpatient basis to allow the radiation implant to work over an extended period of time.  With temporary therapy, the device is taken out after the series of treatment is finished.  For permanent brachytherapy, the seed implant is left in place and the seeds slowly lose their radioactivity in about a year. 

Intensity–modulated radiation therapy (IMRT)

Intensity–modulated radiation therapy (IMRT) represents a breakthrough advance in radiation oncology.  With IMRT, highly accurate three–dimensional radiation is administered after the lung and pleura have been removed.  IMRT allows treatment in areas of the body that previously could not safely tolerate conventional radiation.  This new technology may provide better results and less toxicity than traditional external beam radiotherapy.

IMRT requires detailed planning and close collaboration among the surgeon, radiation oncologist, physicist and radiation therapist.  The areas believed to carry a high risk for cancer recurrence are plotted out on CT scans and then analyzed with a computer that performs three–dimensional dosage calculations.  With IMRT, high doses of radiation may be precisely delivered to the entire chest cavity. 

 

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