Proton Therapy – “Clear Advantages” in Treating Mesothelioma

A new study suggests that an up-and-coming type of radiotherapy may do more good – with less damage – than the current gold standard radiation treatments for mesothelioma.

Currently, most mesothelioma patients who are treated with radiotherapy receive the conventional electron-based variety. While radiation can sometimes shrink a tumor, one of the major risks is that the ionized particles will also do permanent damage to the healthy tissue around it. This can be particularly challenging in mesothelioma because the tumors tend to be thin, spread across a large area, and are located close to critical organs such as the heart and lungs.

Like electron-based radiotherapy, proton-based radiotherapy works by ionizing radiation to kill cancer cells and shrink tumors. But in recent years, protons have been shown to have some advantages over electrons for certain types of cancers, including mesothelioma. Because protons tend to lose energy more quickly as they slow down, they make it possible to deposit a higher dose of radiation into a mesothelioma tumor without damaging healthy tissue beyond it.

When paired with intensity-modulation technology to conform the beam to the tumor shape, proton therapy can be made even more precise. A group of doctors in Italy recently tested intensity modulated proton therapy (IMPT) against intensity modulated radiation therapy (IMRT) in 7 mesothelioma patients. For both techniques, they made conventional dose comparisons and compared the probability of harm to normal tissues close to the mesothelioma tumor.

The researchers report that IMPT allowed for a ‘slight improvement’ in target covered but ‘clear advantages’ in conformity and homogeneity – or evenness – of the radiation dose throughout the mesothelioma tumor. Reporting on their findings in a European medical journal, the team found IMPT treatment of mesothelioma to be equal to IMRT for tumor dose delivery but safer for the liver and the kidney closest to the tumor. They also found a “very large reduction in mean dose” of radiation to the lung opposite the mesothelioma tumor with IMPT.

The newest findings confirm what a team of Swiss researchers found when they tested proton therapy for mesothelioma in 2010. That study, which tested adjuvant proton therapy after surgery, concluded that “proton therapy accomplished additional dose sparing of most organs at risk compared with IMRT.” Although there are an increasing number of proton cancer treatment center nationwide, they are still relatively rare. The therapy is still expensive compared to standard treatment and data on its use for mesothelioma, while promising, is still sparse.

Sources:

Lorentini, S et al, “Adjuvant intensity-modulated proton therapy in malignant mesothelioma: A comparison with intensity-modulated radiotherapy and a spot size variation assessment”, February 10, 2012, Strahlentherapie und Onkologie, Epub ahead of print. Krayenbuehl, J et al, “Proton therapy for malignant pleural mesothelioma after extrapleural pleuropneumonectomy”, October 1, 2010, International Journal of Radiation Oncology, Biology, Physics, pp. 628-34.