Radiation for Mesothelioma: Could Proton Therapy Be the Answer?

Researchers at the Maryland Proton Therapy Treatment Center say a highly-targeted version of proton beam radiation could be the future of radiotherapy for malignant pleural mesothelioma.

In a new journal article, doctors at the center detail the evolution of radiation treatment for pleural mesothelioma, from standard photon-based therapy to targeted proton therapy.

“Radiation therapy has historically been used [for mesothelioma] only in the palliative setting or as adjuvant therapy after extrapleural pneumonectomy,” notes the report.

But the researchers go on to say that radiotherapy advances such as intensity-modulated radiation therapy (IMRT) and a more precise form of proton beam therapy called pencil-beam scanning, are changing the value of radiotherapy for mesothelioma patients.

Radiation’s Role in Pleural Mesothelioma Treatment

Radiation works to kill cancer cells by permanently damaging the DNA that is their roadmap for growth, metabolism, and replication. When the DNA molecules are too scrambled to direct the life of the mesothelioma cell, the cell dies. If enough cells die, a tumor can be destroyed.

The challenge in radiotherapy is always how to target the tumor with sufficient amounts of cell-destroying radiation, without simultaneously damaging healthy surrounding tissue.

 

While targeted radiotherapy can be an effective treatment for certain types of tumors, the challenge for people with malignant mesothelioma is that 1) mesothelioma tumors are not uniform in size or shape and 2) pleural mesothelioma tumors lie close to other critical organs like the lungs and heart.

This is why even targeted radiotherapy systems like IMRT have primarily been used to slow down pleural mesothelioma tumor growth prior to surgery, to help control mesothelioma symptoms, or to destroy residual mesothelioma cells after surgery.

Proton Beam Therapy Could Change Mesothelioma Care

Proton Beam Therapy is the “new kid” on the radiotherapy block. Although the technology has existed for decades, it is only in the last few years that it has begun to get more attention from the cancer community as a potential treatment option.

Like photon-based radiotherapy, proton-based radiotherapy uses ionizing radiation to kill cancer cells and shrink tumors. But some studies have suggested that protons may be safer than photons.

Because they tend to lose energy more quickly as they slow down on their way through tissue, the theory is that protons make it possible to deposit a higher dose of radiation into a mesothelioma tumor without damaging healthy tissue around it. Research has produced mixed results.

The newest study from the Maryland Proton Treatment Center focuses on a particular type of proton therapy called pencil beam scanning (PBS) in the treatment of pleural mesothelioma tumors..

While standard proton therapy treats the entire tumor with the same dose of protons at the same time, PBS allows the doctor to adjust the intensity of the beam for each layer of the mesothelioma tumor. Magnets are used to focus the beam, allowing for higher dosing in areas that need it.

The researchers say the added safety and precision of PBS make it possible to use it “as definitive therapy for patients with recurrent or unresectable disease.”

“PBS proton therapy has the potential to deliver high doses of irradiation to the entire effected pleura while significantly reducing doses to nearby organs at risk,” writes author Shahed Badiyan. The article appears in the journal Translational Lung Cancer Research.

Sources:

Badiyan, SN, et al, “Proton beam therapy for malignant pleural mesothelioma”, April, 2018, Translational Lung Cancer Research, pp. 189-198

“PBS, the Future of Proton Therapy”, July 3, 2007, Proton Therapy Today