Intensity-Modulated Radiation Therapy

IMRT, or intensity-modulated radiation therapy, is a type of radiation treatment that can be used to treat certain types of cancer, usually as part of a multimodal approach that also 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, but it is sometimes used for these.

What makes IMRT different from traditional radiation therapy is that changes the intensity of the dosing to help protect healthy tissue around the tumor. This not only protects healthy tissue, but allows doctors to deliver stronger doses of radiation more directly to the tumor, hopefully for more effective treatment outcomes. Even though the administration of the radiation is more precise, there are still risks and side effects associated with this treatment.

What is IMRT?

Intensity-modulated radiation therapy is a more advanced form of radiation therapy than the traditional treatment. Radiation therapy uses high energy beams, like X-rays or gamma rays, to target and kill cancer cells. The beam must be targeted and aimed at the tumor to minimize the damage to healthy cells. Radiation does not discriminate between cancer cells and healthy cells and will damage and kill either.

With IMRT a computer is used to control the linear accelerators that are used to produce the beam of radiation. The computer varies the intensity of the radiation in a specific way depending on the individual. This results in precise doses of radiation that conform to the three-dimensional shape of a tumor. The modulation of the intensity allows for stronger doses of radiation to hit 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

Mesothelioma is not one of the types of cancer that is typically treated with IMRT, but for some patients it may be an option. Research is ongoing to determine how effective this treatment may be for mesothelioma patients, along with chemotherapy and surgery. Pleural mesothelioma is often treated first with surgery to remove the bulk of tumors and then with chemotherapy or radiation to eliminate any remaining cancer cells and to delay remission.

One study used IMRT on patients being treated for mesothelioma. The patients first underwent extrapleural pneumonectomy procedures, radical surgery to remove the lung, pleura, lymph nodes, and diaphragm from one side of the chest cavity. This is a risky surgery, but for patients in earlier stages of the disease it represents one of the only ways to achieve any significant extension in life expectancy. Radiation after the treatment further helps delay a recurrence. In this study the patients who underwent IMRT after surgical removal of cancerous tissues did help control the spread of the cancer in the chest cavity.

Studies have also investigated the use of a variation on IMRT, called hemithoracic radiation, on patients with pleural mesothelioma with promising results. In one trial with this technique, 50 percent of patients were still alive one year after treatment. It also resulted in less damage to the healthy lung than IMRT. The research on this highly-focused type of IMRT is still ongoing, but holds great promise for treating pleural mesothelioma.

How the Procedure Is Done

The process of using IMRT begins with imaging scans of the area of the body to be treated with radiation. CT, MRI, or PET scans may be used to create detailed, three-dimensional images of the tumors to be targeted. This is what the computer will use to conform the radiation doses to the specific shape and size of an individual tumor. It takes time to plan the treatment specifically for each individual, so it may be a week or two between taking imaging scans and beginning the IMRT treatment.

To be treated, the patient is situated in the right position to aim the radiation at the correct part of the body. The medical staff will set everything up and then leave the room to watch from a safe place, protected from the radiation in the room. Certain parts of the patient’s body may be covered to protect against radiation. The process will then take between 15 and 30 minutes and should not hurt or be uncomfortable.

Benefits of IMRT

Because IMRT is designed to focus the highest doses of radiation to the tumor and to minimize radiation impact on surrounding tissues, this type of therapy has a few important benefits. One is that the patient is able to receive higher doses of radiation than using traditional therapy. With higher doses, this technique can produce better results in shrinking tumors. Another benefit is that there are fewer side effects for the patient than with traditional radiation therapy because healthy tissue is better protected.

Side Effects and Risks

For most patients undergoing IMRT, the risks and side effects are minimal and less than with traditional radiation. This is because the radiation is so focused on the tumor and not on healthy tissue. If a patient does experience side effects, they are similar to those seen with traditional radiation: hair loss, soreness, or swelling at the treatment site, headaches, nausea, vomiting, digestive problems, difficulty swallowing, and changes in the bladder and urinating.

Rarely, any type of radiation can cause later side effects, which occur only months later. These include changes to the kidneys, brain, lungs, or spinal cord, gastrointestinal damage, infertility, joint problems, lymphedema, and secondary cancer. These are all extremely rare with IMRT but are always potential risks that should be considered. An exception to the minimal side effects with IMRT is during treatment for pleural mesothelioma.

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

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