Proton Therapy for Mesothelioma: New Consensus Statement

A group of international experts in radiation oncology say proton therapy for mesothelioma may be a safer alternative to standard radiotherapy. 

Proton therapy uses protons instead of photons to destroy mesothelioma tumor cells. 

The group evaluated both types of radiation therapy. They conclude that proton therapy for mesothelioma is less likely to damage the opposite lung and other organs. 

What is Proton Therapy?

Conventional radiation therapy for mesothelioma uses photons. A radiation oncologist delivers photons into the tumor with a linear accelerator. The photons or X-rays permanently damage the DNA. Damaged mesothelioma cells cannot grow and divide normally and the cells die. 

The downside of standard radiation therapy is that normal tissue absorbs some of the damaging photons, too. This limits how much radiation doctors can use. Even targeted radiotherapy like IMRT cannot prevent this. 

Proton therapy for mesothelioma works the same way. But proton particles behave differently than photons. There is some evidence that they cause more devastating and long-lasting DNA damage.  

Another difference with proton therapy for mesothelioma is how far the energy travels. Photons keep going after they pass through a mesothelioma tumor. They can damage organs on the other side. 

But protons release all their energy inside the cancer cells. This may be especially beneficial for pleural mesothelioma patients. 

Guidance for Clinicians

Pleural mesothelioma grows on the lining around the lungs. The tumors are close to vital organs like the heart, lungs, stomach, and kidneys. This makes it hard to deliver a cancer-killing dose with standard radiotherapy. Doctors have mostly used radiotherapy to shrink mesothelioma tumors before surgery. 

Proton therapy for mesothelioma may be safer and more effective. Doctors can use a higher dose without damaging other organs. The study group evaluated the clinical data on proton therapy to reach a consensus.

“The physical properties of proton therapy result in better sparing of normal tissues when treating the pleura, both in the post-pneumonectomy setting and the lung-intact setting,” says the new Consensus Statement. “Compared to photon radiation, there are dramatic reductions in dose to the contralateral lung, heart, liver, kidneys, and stomach.”

But proton therapy for mesothelioma is still challenging. One problem is the variety of different types of tissue in the chest. Another is the fact that organs like the lungs and heart are constantly moving. Movement and differing densities can make it hard to be precise.

Proton-based radiation is an evolving therapy.  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. It is not yet widely available.

The new consensus statement on proton therapy for mesothelioma is designed to be a guide for doctors, insurance companies, and researchers. 

Source: 

Zeng, J, et al, “Consensus Statement on Proton Therapy in Mesothelioma”, Mary 24, 2020, Practical Radiation Oncology, Epub ahead of print, https://www.practicalradonc.org/article/S1879-8500(20)30117-X/pdf