Overview of Proton Radiation Therapy for Mesothelioma Cancer (Science, Benefits, and Data)

Where traditional radiation fails in treating rare and deadly cancers like mesothelioma, proton radiation succeeds.

Proton radiation therapy is one of the fastest-growing types of cancer treatment today, a type of radiation therapy surging in popularity and use for a wide range of benefits and reasons. These benefits all apply to the treatment of mesothelioma cancer as well.

Despite the surge in awareness and popularity, many people don’t know what proton radiation is or that it exists – or that there are different radiation types to treat cancer.

Mesothelioma Guide has an overview of proton radiation, including what it is, how proton radiation treatment works, the benefits of this type of radiation, and the data that has been released so far for how proton radiation helps people diagnosed with mesothelioma cancer.

 

What Is Proton Radiation?

Proton radiation, also called proton beam radiation, is a targeted cancer treatment. Proton radiation waves are sent via a machine into the patient’s body to target tumors. The difference between proton radiation and other types of radiation is how precise the radiation beam is and how focused and narrow the beam is on the target.

Lung cancer and pleural mesothelioma are two cancers that can be treated with proton radiation. Cancer cells can hide in the thin tissue lining near the lungs – called the pleura – or in the space between the lungs, called the mediastinum. Radiation can target these small chunks of cells before or after surgery.

Pleural mesothelioma is the type diagnosed in 75%-80% of mesothelioma cases. The other type is peritoneal mesothelioma, which starts in a thin lining (peritoneum) wrapping around the abdominal cavity.

Radiation therapy is typically not used to treat peritoneal mesothelioma. Proton radiation therapy’s benefits of being more targeted may open the door for radiation for peritoneal mesothelioma.
 

What Is Radiation for Cancer?

Proton radiation is essentially an evolution of radiation therapy for cancer, a less-invasive type of treatment than chemotherapy or surgery.

According to the National Cancer Institute, radiation therapy (also called radiotherapy) sends high doses of radiation waves to kill cancer cells and shrink tumors. Another use of radiation is for X-rays. Doctors use low doses of radiation to see inside your body, as with x-rays of your teeth or broken bones.

Radiation for cancer uses higher doses because the goal is to reach deep inside the body and burn the tissue that’s targeted. The traditional type of radiation is called photon radiation, or external beam radiation therapy.

While radiation treatment is less invasive and less impactful than chemotherapy or surgery, it also has less impact in killing tumors. Doctors usually prefer combining radiation with another treatment.

Radiation can also damage healthy tissue cells. The high doses of radiation waves can cause radiation spray, which is when radiation can impact healthy tissue near the targeted tumor cells.

In the case of mesothelioma, which starts near the lungs and often spreads to the lungs, radiation spray can damage the lungs. This damage could be impactful, even deadly, for patients.
 

Overview of Benefits of Proton Radiation Therapy for Cancer

Proton radiation causes less spray than other types and has a tighter beam, which has many benefits, most of which is the ability to safeguard healthy tissue. Radiation oncologists can also use higher dosages.

“While traditional photon radiation pierces through tumors, protons stop at the intended target, limiting irradiation of the surrounding tissue and organs and minimizing patient exposure to excess radiation,” a representative from the New York Proton Center said in an email exchange with Mesothelioma Guide.

Proton therapy “is particularly effective in targeting difficult-to-treat tumors” because doctors can deliver a higher dose to the disease location. Pleural mesothelioma is considered a difficult-to-treat cancer type, mostly due to how fast it spreads and how close the tumors are to the lungs.

 

History of Proton Beam Radiation Therapy

Proton radiation therapy was created in the 1940s, but not until 1990 did the first hospital-based, treatment-dedicated institution open. That year is when Loma Linda University Cancer Center made history. Almost 30 years later, many other hospitals have made this treatment more accessible.

The New York Proton Center opened in early 2019, making it the 28th such medical institution in the United States. Twenty opened from 2012-2019, and a dozen or so more followed in the last few years.

A total of 41 are operating as of 2023, according to the National Association of Proton Therapy.
 

Increase in Use of Proton Radiation for Mesothelioma

A study in JAMA Oncology explored the growing use of this new type of radiation. Nearly 6 million cases from the National Cancer Database were included in the study. The overall use of proton radiation tripled from 2004-2018.

The researchers reported in JAMA Oncology that 1.2% of patients used proton radiation in 2018. Fourteen years earlier, the percentage was 0.4%.

 

Why Proton Radiation Therapy for Mesothelioma Is Better Than Other Radiation Types

A 2017 report written by 16 radiation experts spanning 12 hospitals examines the benefits and drawbacks of each radiation approach for pleural mesothelioma, the type of mesothelioma that starts in the lining around the lungs (pleura).

The conclusion? Proton radiation is the recommended type of radiation for pleural mesothelioma.

We at Mesothelioma Guide interviewed Dr. Charles Simone, the chief medical officer of the New York Proton Center. He’s also one of the 16 authors for the report. He provided context on why proton radiation therapy is so beneficial in combating pleural mesothelioma — and why, most importantly, it’s the safest radiotherapy option.

“I think people are now more comfortable delivering (proton radiation),” he said. “I think it’s more evident that mesothelioma is a radiosensitive cancer.”

He added that he believes “radiation is coming back in favor” thanks to the evolution and emergence of proton radiation.
 

Mesothelioma Radiation, Pneumonitis, and Damage to the ‘Contralateral Lung’

The long-standing issue with mesothelioma radiation is the therapy can damage healthy tissue, even that of essential organs. Traditional photon radiation, and even the more-targeted and more-effective intensity-modulated radiation therapy (IMRT), can lead to a condition called pneumonitis.

Pneumonitis involves damage to healthy lung tissue. Mesothelioma radiation inevitably leads to damage to the lung closest to where pleural mesothelioma forms. What should be restricted is damage to the lung on the opposite side of the thorax.

This lung is called the “contralateral lung.” Contralateral is defined in medical terminology as the opposite side of the body. The contralateral lung is the organ on the opposite side of the chest from where pleural mesothelioma originates. That lung is essential to long-term survival and quality of life for mesothelioma patients.
 

Protecting the Contralateral Lung After Mesothelioma Surgery

There are two primary surgeries for this type of mesothelioma: extrapleural pneumonectomy (EPP) and pleurectomy with decortication (P/D). EPP removes the nearby lung from the body. P/D spares the lung and primarily focuses on removing the pleura, which is the narrow space near the lung where this cancer forms.

If a patient undergoes EPP, then the health of the remaining lung is vital. Even after P/D, radiation therapy must be directed on or close to the ipsilateral lung, which is the lung nearest where mesothelioma tumors first start. At least some tissue damage is nearly a foregone conclusion, since mesothelioma usually reaches this lung by the time treatment begins.

“To some extent, we can’t avoid damage,” Dr. Simone said. “That lung never is as ‘good’ as it was before their diagnosis of mesothelioma. Their lung elasticity is never as good as it was before.”

The contralateral lung should be a priority, though, because it can be protected from radiation therapy spray. At high doses, radiation oncologists have difficulty reducing damage to the contralateral lung with traditional radiation and IMRT. According to the report, which cites multiple studies:

• IMRT after EPP led to a 15% rate of severe pneumonitis to the contralateral lung
• IMRT after P/D resulted in a 20% rate of grade 3 or higher pneumonitis to the contralateral lung

“The problem historically has been it’s harder to deliver radiation for mesothelioma because it’s a big area,” Dr. Simone said. “We need to treat the entire hemithorax. … We usually can’t deliver that high of a dose with traditional radiation, even photon radiation or IMRT.

“We either underdose the tumor or lower the dose we are prescribing. Both of those can lead to lower control rates.”
 

How Proton Radiation Avoids Lung Damage and Pneumonitis

The benefit of proton therapy, compared to traditional radiation or even IMRT, is the proton beams stop at the intended target. IMRT is a more targeted approach that limits damage to healthy tissue. It has its benefits, especially compared to traditional X-ray photon radiation, but it still can lead to lung tissue damage.

Proton radiation is the next evolution in this treatment. The proton beams limit excess radiation to surrounding tissue and organs, allowing radiation oncologists to deliver higher doses to the mesothelioma tumors.

“Higher doses have better outcomes and better survival for mesothelioma,” Dr. Simone said.

The paper cites four studies, three involving proton radiation after P/D surgery and one using proton radiation after EPP surgery. In combining the results of the four studies:

• Grade 3 pneumonitis was the most severe amount of damage to the contralateral lung
• Only two of the 39 patients (5.1%) had grade 3 pneumonitis
• Only three of the 39 patients (7.7%) had grade 2 pneumonitis

The pneumonitis rates for proton radiation were lower than those of traditional photon radiation. This is while using the same dose for treatment.
 

Proton Radiation Therapy Reduces Damage to Other Vital Body Parts

In addition to the contralateral lung, radiation can damage tissue on or in the:

• Spinal cord
• Kidneys
• Heart
• Liver
• Esophagus

Proton radiation minimizes the risk for all of these organs and body areas. In every cited study comparing proton radiation and traditional methods, proton radiation delivered a lower amount of scattered radiation to the heart, liver and kidneys.

All of this is evidence that proton radiation can deliver life-extending, tumor-killing effects while minimizing severe side effects.

 

Steps of Proton Radiation Therapy for Mesothelioma

Each mesothelioma case is unique, which means each patient may have a different process for proton radiation therapy. However, let’s lay out a standard process for proton radiation treatment for mesothelioma.

The New York Proton Center in New York has a general schedule to provide a sense of what someone should expect from the treatment:

• The entire session (including preparation and post-radiation conversations) usually lasts one hour.
• Radiation itself lasts around 15 minutes.
• Most patients undergo four or five sessions per week.
• A proton radiation therapy plan can last anywhere from two to six weeks.

 

Find a Proton Radiation Therapy Center Near You

Most patients currently going to the New York Proton Center are from the northeast region of the United States. However, the center is accepting patients from throughout the country.

If attending the New York Proton Center is not feasible for you or your loved one with mesothelioma, then there are other proton centers in each region of the country. We at Mesothelioma Guide can help you find a center that treats mesothelioma and is conveniently located to reduce your travel and other hardships.

Email our lead patient advocate, Karen Ritter, RN, at karen@mesotheliomaguide.com to get the help you deserve right away.

You can also find a list of all the operating proton radiation therapy centers on the National Association for Proton Therapy website. This resource provides locations for all 41 centers, giving you the ability to find one near where you live if you’re interested in proton radiation treatment for mesothelioma.