What Is Proton Therapy for Mesothelioma?

Proton therapy is a type of anti-cancer radiation therapy that allows for greater precision than traditional options, plus reduced side effects. Mesothelioma doctors can treat tumors with higher-energy radiation particles without damaging nearby healthy tissue and organs.

The advanced technology of proton radiation therapy allows physicians to precisely map the mesothelial surface and deliver treatment at exact angles. With traditional radiation for mesothelioma, particles pass through cancer tissue and damage organs behind the cancer site, such as the heart, lungs or kidneys.

While currently only available at specialized cancer treatment centers, proton therapy can replace traditional radiation in a multimodal treatment plan for malignant pleural mesothelioma (MPM). Due to the reduced risk of complications, proton therapy is also a suitable treatment for patients with late-stage or end-stage disease.

Proton therapy can improve survival when combined with other treatments. In a 2018 clinical trial, mesothelioma patients who underwent surgery and received proton therapy, phototherapy and chemotherapy had a median survival of 30.3 months from diagnosis.
Source: Photochemistry and Photobiology, 2018

Radiation oncologists prescribe proton therapy in cycles of up to eight weeks, but the length of treatment depends on the dose of radiation prescribed. Patients undergoing higher doses will have shorter cycles, while lower doses require a more extended treatment period.

Treatment clinics schedule a simulation session and consultation before patients undertake proton therapy. This preparation maps the three-dimensional shape of the patient’s cancer that the protons will target. Treatments are painless and take about 30 to 90 minutes in a process similar to receiving an MRI scan.

Proton Therapy vs. Traditional Radiation Therapy

The advancements of proton therapy offer substantial benefits over conventional radiation therapy options. While both methods aim to damage the DNA within cancer cells, traditional radiation uses photons, which make up visible light, radio waves and X-rays. Protons are sub-atomic particles that are a part of all molecules.

Comparing Traditional Radiation and Proton Therapy

Both types of radiation damage the DNA within tumor cells, preventing cellular reproduction and causing cell death. Protons are heavier than photons, allowing physicians to direct the particles to deposit at specific sites within the tumor without passing through to healthy tissue.
Radiation oncologists can use intensity modulation with both proton and traditional radiation therapy to control how much energy penetrates each tumor site.Physicians and medical physicists calculate the density of tissues impacted by proton therapy and can calibrate the machinery to account for patient movement.
Treatments with both methods usually take less than one hour and are painless. The most common side effects are skin irritation and mild nausea.Traditional radiation releases a significant amount of energy at the point of entry, causing skin irritation and more noticeable side effects than proton therapy.
Medicare generally covers most instances of both therapies, depending on the patient’s cancer type and the doctor’s recommendation.Physicians can more easily integrate proton therapy into a multimodal treatment plan for mesothelioma due to a decreased risk of complications and side effects.

Eligibility for Mesothelioma Proton Therapy

Patients with early-stage disease and localized tumors are the best candidates for proton therapy. Many stage 4 mesothelioma patients do not receive a diagnosis until the condition is in its later stages, which may make them ineligible for proton therapy.

Eligibility factors for proton radiation therapy include:
  • Good overall health to endure a multimodal treatment plan
  • Proximity to the treatment center for daily appointments
  • Body weight less than 360 pounds to accommodate machinery
  • Solid, localized tumors with defined borders, although metastatic patients with specific cancer types may be eligible

As of August 2020, proton therapy remains under investigation for use in rarer subtypes of mesothelioma, including peritoneal and pericardial. There are currently only 27 proton therapy centers operating within the United States, and data on proton effectiveness for rarer cancers are lacking.

An additional benefit of radiation therapy is that patients who previously underwent traditional radiation remain eligible for proton therapy. Typically, patients who undergo X-ray radiation therapy are ineligible for additional courses in a subsequent treatment plan. With proton therapy, there is a minimized risk of developing secondary cancer from radiation exposure.

Potential Side Effects

Side effects of proton therapy are considerably fewer and less severe than with traditional mesothelioma radiation therapy. The side effects that you experience will depend on the area of your body undergoing treatment and the dose of radiation you receive.

Common side effects of proton therapy for malignant pleural mesothelioma patients include:
  • Skin irritation or redness
  • Fatigue or general malaise
  • Chest soreness
  • Throat soreness

How Proton Therapy Fits Within Mesothelioma Treatment

Due to its generally safer approach, physicians can prescribe proton therapy at many different points throughout mesothelioma treatment. Proton therapy has shown effectiveness both before and after first-line treatment and can supplement chemotherapy and surgery in a multidisciplinary treatment plan.

Neoadjuvant Therapy: Doctors prescribe neoadjuvant treatments before a patient receives their first course of primary treatment, such as chemotherapy for mesothelioma. There is limited data on the effectiveness of proton therapy as a neoadjuvant option. However, doctors use conventional radiotherapy in the neoadjuvant setting and may explore proton therapy in the future.

First-Line Treatment: First-line therapy is the main treatment course a patient receives after diagnosis. Doctors have historically used radiotherapy complementary to first-line treatments such as chemotherapy and surgery for mesothelioma patients. However, proton therapy is showing success as a primary first-line treatment for lung cancer in several clinical studies.

Adjuvant Therapy: After surgery, doctors treat patients with adjuvant therapy to destroy cancer cells that may remain after the procedure. Proton therapy is becoming a popular choice for physicians to prescribe after performing pleurectomy and decortication surgery. Proton therapy in the adjuvant setting can prolong the recurrence of cancer and improve survival rates.

Proton Therapy in Mesothelioma Clinical Trials

Researchers continue to study proton therapy in mesothelioma clinical trials to test its effectiveness and safety. Mesothelioma patients may be eligible for specific proton therapy trials depending on their cancer type and location.

One example is a phase III trial investigating the addition of proton therapy to a combination regimen of surgery and chemotherapy for malignant pleural mesothelioma. The study is currently enrolling 150 patients through Memorial Sloan Kettering in New York and New Jersey and the Ohio State University Comprehensive Cancer Center.