A form of highly-targeted radiation therapy for mesothelioma is better than it used to be, but is still risky. That is the message of a recent article on intensity-modulated radiation therapy (IMRT) in Seminars in Thoracic and Cardiovascular Surgery.
Author Kenneth E. Rosenzweig, MD, a Radiation Oncologist with Mount Sinai Hospital in New York, reviewed recent studies on IMRT and mesothelioma. He concludes that, while the “troubling toxicity” associated with IMRT when it was first introduced has not been entirely eliminated, the fact that clinicians now have more experience with it is making a positive difference for mesothelioma patients.
Before targeted therapies like IMRT were available, high-dose radiation was not usually a feasible option for mesothelioma since the irregular shape of the tumor made it nearly impossible to avoid toxic overdoses to surrounding healthy tissue. But IMRT offers the ability to conform the radiation dose to the tumor, avoiding some of the toxicity of previous radiotherapy approaches.
Dr. Rosenzweig reviewed studies of IMRT therapy after pneumonectomy (lung and pleura removal) as well as pleurectomy (removal of pleura only). After pneumonectomy, the studies suggest that the biggest challenge with IMRT is minimizing the radiation dose to the remaining lung. Mesothelioma patients who had the best response to IMRT after pneumonectomy were those in whom less than 5% of the contralateral lung received a dose of 20Gy. In mesothelioma patients who still had both lungs, Rosenzweig found that the mean lung dose could be as high as 20Gy without causing serious problems.
But IMRT for mesothelioma still has limitations. In the studies reviewed by Rosenzweig, the rates of grade 3 or worse radiation-induced pneumonitis (inflammation of the lung tissue) were 12% to 20%. More concerning is the fact that 3% to 8% of mesothelioma patients studied died of pneumonitis after receiving radiation therapy. The author concludes, “The rates of fatal pneumonitis… demonstrate the considerable toxicity of treatment, even with improved technique.”
All treatments for mesothelioma have their limitations. Although chemotherapy is considered the first-line treatment for mesothelioma, even the recommended pemetrexed/cisplatin combination can increase the chance of serious infections. Most studies have found that a multi-modal approach, including some combination of medication, surgery, radiotherapy and/or experimental treatments such as gene therapy yields the best results.
Rosenzweig, KE, “Current readings: Improvement in intensity-modulated radiation therapy for malignant pleural mesothelioma”, Autumn 2013, Seminars in Thoracic and Cardiovascular Surgery, Epub ahead of print.