Mesothelioma patients may receive radiation therapy as part of their treatment regimen, but without precise delivery, radiation can harm healthy cells as well as the tumors. Proton therapy is one of the most specialized types of radiation particle therapy, beaming highly energized protons directly at cancerous growths.
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Since protons can only travel through several centimeters of tissue, they rarely extend outside of the treatment area. This reduces the potential for side effects that occur when radiation therapy impacts healthy surrounding tissues and organs, such as the lungs (in the case of pleural mesothelioma) or the heart (in the case of pericardial mesothelioma).
Because this therapy is a site-specific treatment, it is typically not given to patients whose cancer has spread throughout the body (called metastasis). Mesothelioma patients may be eligible for the procedure if their cancer has not metastasized, but patients with advanced stages of the cancer (when the cancer has spread) are often more responsive to other treatments such as chemotherapy.
Proton therapy is delivered externally, making it a non-invasive type of treatment. Protons can be directed at the tumor from a steady beam or through a moving beam in a technique known as pencil beam scanning proton therapy -- in which the radiation oncologist directs the beam to desired areas, avoiding healthy areas, vital organs or sensitive areas that have already been radiated. Additionally, the radiation therapist can adjust the intensity of the protons so that they are not strong enough to penetrate into tissues or organs that lie beneath the tumor. This allows the majority of radiation to remain within the cancerous cells.
This therapy is delivered in cycles of up to seven or eight weeks. The length of treatment is often dependent on the dose of radiation required to treat the cancer; higher doses of radiation are given in shorter cycles while lower doses of radiation are delivered over a longer period of time. To prepare them for the procedure, patients will undergo a simulation session approximately a week before treatments are set to begin.
The proton beam provides much more conformal radiation, which means higher doses to tumors and lower dosages to critical structures nearby. – Dr. Joe Chang, M.D., Ph. D., MD Anderson's UT Department of Radiation Oncology
During a therapy session, patients are positioned on a device that prevents the body from moving. Using markings made during the simulation session, the radiation therapist will position the radiation beam at the area of the body requiring treatment and administer the dose from a control room. Throughout the 30- to 90-minute treatment sessions, patients will be able to communicate with their radiation therapist via a two-way intercom. The procedure is painless, and patients are not considered to be radioactive after these sessions.
Unlike other forms of radiation therapy, this therapy does not subject healthy tissue to high doses of radiation. Only 20 percent of the radiation delivered by proton therapy is deposited into the surrounding tissue, which typically is too weak to cause substantial side effects. A study of lung cancer patients who received proton therapy at the M.D. Anderson Cancer Center in Houston found that the participants were less likely to develop esophagitis, pneumonitis and bone marrow toxicity, three of the major side effects associated with other types of radiation therapy. The side effects that do arise are typically similar to side effects experienced with other forms of radiation, but on a much milder scale. These may include skin redness and temporary hair loss in the area being treated.
For a detailed description and visual of how proton therapy works, watch this video from the University of Florida Proton Therapy Institute.
Proton therapy is primarily approved for patients with cancer in only one location. Mesothelioma patients with Stage I cancer may be eligible for the procedure, since the cancer has not spread. Because mesothelioma is a rapidly spreading disease and many patients are diagnosed in later stages when the cancer has already spread, this therapy may not be an option for many patients.
Did you know? One study found that pleural mesothelioma patients who underwent proton therapy showed lower post-treatment radiation levels in the kidneys, liver, heart, spinal cord and non-cancerous lung than the levels in the organs of patients who received another form of radiation therapy.
Thankfully, advancements in early detection of mesothelioma are helping more patients to qualify for proton therapy by detecting the cancer before it spreads. Mesothelioma patients who do receive this therapy are often undergoing a combination of the treatment with other procedures, such as surgery. This approach, known as multimodal therapy, combines treatments to more effectively fight the cancer than with a single treatment.
Regarded as one of the most sophisticated types of radiation delivery, proton therapy has become increasingly prevalent since its development in the 1950s. It has been used in clinical cancer treatment in the United States since 1990. As of 2009, there were 38 worldwide facilities dedicated to the therapy, including the University of Florida Proton Therapy Institute and the Proton Therapy and Treatment Center at Loma Linda University.
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