Intensity-Modulated Radiation Therapy

Intensity-modulated radiation therapy (IMRT) is used to treat certain types of cancer, usually as part of a multimodal approach that includes chemotherapy and surgery. Cancers typically treated with IMRT include prostate cancer, central nervous system cancers, and head and neck cancers. Research into the effectiveness of IMRT for mesothelioma or asbestos lung cancer is limited. However, IMRT is sometimes used to treat these diseases.

What makes IMRT different from traditional radiation therapy is the ability to change dosing intensity to protect healthy tissue around the tumor. IMRT also allows doctors to deliver stronger doses of radiation more directly to the tumor, hopefully producing more effective treatment outcomes. There are still risks and side effects associated with this treatment, even though radiation administration is more precise, .

What is IMRT?

Intensity-modulated radiation therapy is more advanced than traditional radiation therapy. Radiation therapy uses high energy beams, like X-rays or gamma rays, to target and kill cancer cells. To minimize damage to healthy cells, the beam must be properly aimed at the tumor. Radiation does not discriminate between cancer cells and healthy cells so will damage and kill both.

IMRT uses a computer to control the linear accelerators that produce the radiation beam. The computer varies the radiation intensity, depending on the individual, in a specific way. This results in precise doses of radiation that conform to the three-dimensional shape of a tumor. The modulation of intensity allows for stronger radiation doses to contact the tumor, while doses to surrounding tissue are minimized. The computer uses detailed images of the patient’s tumor, based on CT or MRI scans.

IMRT and Mesothelioma

Although it is an option for some patients, IMRT is not typically used to treat mesothelioma. Research is ongoing to determine IMRT’s efficacy for mesothelioma patients, along with chemotherapy and surgery. Pleural mesothelioma is typically treated with surgery first, allowing the bulk of the tumors to be removed. Afterward, chemotherapy or radiation eliminates any remaining cancer cells.

One specific study used IMRT on mesothelioma patients. These patients first received extrapleural pneumonectomy procedures. Extrapleural pneumonectomy is a radical surgery that removes the lung, pleura, lymph nodes, and diaphragm from one side of the chest cavity. While it is a risky surgery, for patients in earlier stages of the disease it is one of the few ways to extend life expectancy. After this surgery, radiation helps delay a recurrence. In this study, after surgical removal of cancerous tissues, IMRT did help control the spread of cancer in the chest cavity.

Studies have also investigated hemithoracic radiation, a variation of IMRT, on patients with pleural mesothelioma and found promising results. In one trial, 50 percent of patients were still alive one year after treatment. This procedure also caused less damage to the healthy lung than IMRT. Research on this highly-focused type of IMRT is ongoing but holds great promise for treating pleural mesothelioma.

How the Procedure Is Done

IMRT begins with imaging scans of the area to be treated. CT, MRI, or PET scans may be used to create detailed, three-dimensional images of targeted tumors. Computers will use these images to conform radiation doses to the specific shape and size the tumor. Because planning individual treatments takes time, there may be a week or more the imaging scans before IMRT treatment.

To be treated, the patient is properly positioned so the radiation will hit the correct part of the body. Once everything is in place, the medical staff will leave the room to watch from a safe place, protected from radiation in the room. Non-related parts of the patient’s body may be covered for safety. The process takes between 15 and 30 minutes and is not painful.

Benefits of IMRT

Because IMRT is designed to focus the highest doses of radiation to the tumor, minimizing radiation impact on surrounding tissues, this therapy has important benefits. One benefit is a higher radiation dosage to cancerous tissue. With higher doses, this technique produces better tumor-shrinking results. Another benefit is fewer side effects for the patient.  Because there is less damage to healthy tissue, this procedure produces fewer side effects.

Side Effects and Risks

For most patients undergoing IMRT, risks and side effects are minimal because radiation is focused on the tumor. If a patient does experience side effects, they are similar to those seen with traditional radiation. Possible side effects include hair loss, soreness or swelling at the treatment site, headaches, vomiting, nausea, digestive problems, difficulty swallowing, and changes in urination.

Any type of radiation treatment can cause side effects that occur months later. While these side effects are rare, they include changes to the brain, lungs, kidneys, or spinal cord, gastrointestinal damage, infertility, joint problems, lymphedema, and secondary cancer.

One major concern with radiation therapy is toxicity, or radiation damage to healthy tissue. While minimal for other types of cancer, risks are higher for patients with pleural mesothelioma. IMRT treatment for pleural mesothelioma may result in a condition called radiation pneumonitis. This condition is caused by damage to the healthy lung from radiation doses used to treat the other side of the chest cavity.  It is characterized by inflammation of the lung and may lead to irreversible damage that worsens over time, ultimately leading to respiratory or heart failure. It can be fatal.

IMRT is an example of advances in medical research and cancer treatment. Radiation therapy is an important part of multimodal treatment of mesothelioma and other cancer types. Although using IMRT for mesothelioma treatment is currently limited, it has potential to be a useful technique for future patients.