Proton Therapy

Proton therapy is an alternative to traditional radiation therapy. It allows doctors to direct more energy into tumors without increasing the risk of collateral damage to vital organs, which mesothelioma tumors usually form around.

Recent advances in technology have allowed radiologists to more precisely locate a tumor in the body and control the angle and intensity of the beam directed at it. With traditional radiation, however, it is difficult for radiologists to overcome the fact mesothelioma typically forms near vital organs extremely vulnerable to radiation damage.

For pleural mesothelioma, these organs include the lungs, heart and liver. For pericardial mesothelioma, they include the intestines and kidneys. The esophagus, spine and bone marrow are all highly susceptible to radiation damage as well.

Proton Therapy Facts

  • Allows radiologists to safely administer higher doses of radiation

  • Reduces risk of radiation damage to vital organs

  • Can replace traditional radiation in a multimodal treatment plan

  • Available only at specialized cancer treatment centers

Proton therapy offers one solution to this problem. By using a beam of protons — rather than a conventional beam of photons — radiologists can increase the amount radiation cancer cells receive and decrease the amount nearby healthy tissues receive. The result is a radiation treatment with a lower risk of complications and potentially greater effectiveness.

The highly targeted nature of proton therapy means it is best suited for treating a localized, early-stage tumor. However, when combined with chemotherapy and radiation as part of a multimodal treatment approach, proton therapy has proven at least as effective as traditional radiation.

There is not enough hard data yet to say whether proton therapy is more effective than other types of radiation therapy for mesothelioma, but early reports from pioneering doctors and cancer survivors suggest the technology shows promise.

“The proton beam provides much more conformal radiation, which means higher doses to tumors and lower dosages to critical structures nearby.”

— Dr. Joe Chang, MD Anderson Cancer Center Department of Radiation Oncology

Proton Versus Traditional Radiation Therapy

Proton therapy and traditional radiation therapy share many of the same basic features:

  • Both seek to damage cancer-cell DNA, preventing reproduction or causing cell death.

  • Both types of radiation can be “intensity modulated,” which means a computer controls precisely how much radiation is aimed at each part of the tumor.

  • The treatments are quick and painless, with each session typically lasting less than an hour and causing only mild side effects.

The differences between the two treatments come from the types of energy beam involved. Traditional radiation uses photons, which are what electromagnetic rays (such as x-rays, radio waves and visible light rays) are made of. Protons, on the other hand, are one of the basic building blocks of matter, along with neutrons and electrons.

Photon and proton beams interact with a cancer patient’s body in distinct ways.

Photons (Traditional Radiation) Protons
Deposit much of their energy as soon as they enter the body Deposit only a small fraction of their energy when they enter the body
Deposit some of their energy in the tumor, but not as much as the healthy tissue in front of the tumor Slow down and come to a stop in the tumor, where they deposit all their remaining energy
Deposit some of their remaining energy in the healthy tissue behind the tumor and then exit the body on the other side Leave the healthy tissue behind the tumor mostly unaffected

With traditional radiation, doctors can only control the angle the beam enters the body and how much radiation all the tissue in its path receives. With proton therapy, however, doctors can also decide where the beam should stop and release the majority of its energy.

For example, if a tumor is 4 centimeters beneath the surface of the patient’s skin, the radiologist can set the speed of the protons so they come to a stop exactly 4 centimeters after entering the patient’s body. The science behind this is complex, because the radiologist has to account for the different densities of the tissues in the body as well as the movement of the tumor when the patient breathes.

Nevertheless, an experienced radiologist with the right proton therapy equipment has more control than they would with a traditional radiation machine. This means they can safely administer a higher dose of therapy, potentially killing more cancer cells.

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Proton Therapy for Mesothelioma

The main barriers to proton therapy are the high cost of the facilities and the high level of expertise required to use them. Researchers have only recently had opportunities to explore the potential of proton therapy for mesothelioma patients.

In 2014, a retrospective study of seven pleural mesothelioma patients confirmed proton therapy reduces the amount of radiation received by the lungs, heart, esophagus and liver compared to traditional radiation therapy.

In 2017, researchers reported on three case studies of pleural mesothelioma patients who received proton therapy after undergoing standard chemotherapy and then major surgery to remove a lung, known as extrapleural pneumonectomy (EPP).

  1. A 71-year-old patient with stage 3 cancer survived for a total of 25 months after the multimodal treatment. At the 20th month, he also began receiving immunotherapy.

  2. A 47-year-old patient with stage 4 mesothelioma survived for only 4 months after the multimodal treatment. During the EPP, the surgeons discovered his cancer had spread further than anticipated, making it more difficult to target with proton therapy.

  3. A 46-year-old patient with stage 3 cancer was still alive at the time of the study’s writing, 14 months after the multimodal treatment. There was no evidence of disease progression, and the patient’s symptoms were manageable with physical therapy and medication.

For patients who receive aggressive treatment while their cancer is still localized, a multimodal approach including proton therapy can help them survive far longer than the typical life expectancies associated with late-stage mesothelioma.

Who Is Eligible for Proton Therapy?

Proton therapy is primarily recommended for patients with localized cancer. Because mesothelioma is a rapidly spreading disease and many patients are diagnosed in a late cancer stage, this therapy may not be an option for many patients.

To be eligible to receive proton therapy as part of an aggressive multimodal treatment approach, patients must also be in good enough overall health to withstand and recover from major surgery.

Other requirements to be a candidate for proton therapy include:

  • Weight of under 360 pounds (equipment may not be able to accommodate larger patients)

  • Ability to commute to or stay near the treatment facility for daily appointments

Mesothelioma is a rare type of cancer, and proton therapy remains an uncommon type of cancer treatment. To find a medical team that specializes in both, patients must seek treatment at a top cancer center, which may involve traveling long distances. Proton therapy also remains a very expensive type of treatment.

Treatment Process

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 for the procedure, patients undergo a simulation session approximately a week before treatments are set to begin.

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 aims the radiation beam at the area of the body requiring treatment and administers the dose from a control room.

Throughout the 30- to 90-minute treatment sessions, patients can communicate with their radiation therapist via a two-way intercom. The procedure is painless and carries a low risk of side effects and complications.

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Karen Selby, RN and Patient Advocate at The Mesothelioma Center

Karen Selby joined Asbestos.com in 2009. She is a registered nurse with a background in oncology and thoracic surgery and was the director of a tissue bank before becoming a Patient Advocate at The Mesothelioma Center. Karen has assisted surgeons with thoracic surgeries such as lung resections, lung transplants, pneumonectomies, pleurectomies and wedge resections. She is also a member of the Academy of Oncology Nurse & Patient Navigators.

Sources
  1. Lee, H. et al. (2017, September). Proton Therapy for Malignant Pleural Mesothelioma: A Three Case Series Describing the Clinical and Dosimetric Advantages of Proton-Based Therapy. Retrieved from https://www.researchgate.net/publication/319949385_Proton_Therapy_for_Malignant_Pleural_Mesothelioma_A_Three_Case_Series_Describing_the_Clinical_and_Dosimetric_Advantages_of_Proton-Based_Therapy
  2. MedlinePlus. (2016, May 20). Proton therapy. Retrieved from http://www.nlm.nih.gov/medlineplus/ency/article/007281.htm
  3. Pan, H. et al. (2014, October 30). Early Experience with Intensity-Modulated Proton Therapy for Lung-Intact Mesothelioma: A Case Series. Retrieved from https://www.oncolink.org/conferences/coverage/ptcog/oncolink-at-ptcog-north-america-2014/early-experience-with-intensity-modulated-proton-therapy-for-lung-intact-mesothelioma-a-case-series
  4. Freeman, S. (2011, May 17). Fewer Side Effects From Proton Therapy in NSCLC. Retrieved from http://www.proton-therapy.org/documents/mda511.pdf
  5. National Association for Proton Therapy. (2010, October 19). Pencil Beam Radiation Offers New Therapy Option for Lung Cancer Patients. Retrieved from http://www.proton-therapy.org/lungcancer_1010.html
  6. Krayenbuehl, J. et al. (2010, October). Proton therapy for malignant pleural mesothelioma after extrapleural pneumonectomy. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/20385451
  7. MD Anderson Cancer Center. (n.d.). Proton Therapy Center: What to Expect. Retrieved from http://www.mdanderson.org/patient-and-cancer-information/proton-therapy-center/what-to-expect/index.html
  8. National Association for Proton Therapy. (n.d.). How It Works. Retrieved from http://www.proton-therapy.org/howit.htm
  9. UF Health Proton Therapy Institute. (n.d.).Proton Therapy for Cancer Treatment. Retrieved from https://www.floridaproton.org/what-is-proton-therapy

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