New way of tracking muscle damage from radiation

Magnetic resonance imaging (MRI) could become a valuable tool for predicting the risk of muscle injury during and following radiation therapy, according to investigators at St. Jude Children's Research Hospital.

The researchers report that MRI can spot the immediate injury done by radiation therapy to the muscles of children undergoing radiation treatment for certain types of soft-tissue cancer. This also indicates that MRI might one day be able to help doctors predict the amount of long-term damage that radiation may cause. A report on these findings appears in the Oct. 25 online issue of Magnetic Resonance Imaging.

The study's findings are significant because as radiation treatments become more advanced and complex, clinicians must have a way to predict the outcomes–including side effects–on specific patients, according to Matthew Krasin, M.D., associate member of the St. Jude Department of Radiological Sciences.

The St. Jude study showed that changes in images taken of muscles before and after radiation therapy for soft tissue sarcoma and Ewing sarcoma are related not only to the amount of radiation the child received, but also to the child's age and the presence of a nearby tumor.

“We hope that detecting these changes at such an early stage may help clinicians predict which patients need an intervention to prevent late damage,” Krasin said. Soft tissue sarcomas are cancers that arise in muscles, fat, blood vessels and other soft tissues. Ewing sarcoma is a cancer that arises in the bone or soft tissue, usually in the arms, legs, pelvis or chest wall.

St. Jude researchers studied the muscles of 13 patients before, during and 12 weeks after they received radiation therapy for soft tissue sarcoma. The team used a technique called quantitative T2 to determine the extent of swelling in tissues before, during and after radiation therapy; and a technique called dynamic enhanced magnetic resonance imaging (DEMRI) to study what happens to the blood supply at a microscopic level.

“These techniques are powerful, non-surgical ways to look into the body and study the microscopic and biochemical changes that are occurring in each patient after radiation therapy,” Krasin said.

The team made 60 images of the same area, including a dynamic view of what was happening in the muscles during a six-minute period following infusion of gadolinium, a contrast agent.

“The rate at which the contrast agent flows in and out of a region, or whether it leaks out of the blood vessel, helps us understand whether the blood supply is in poor or good condition,” Krasin said. “Changes in T2 measurements may indicate an increase in swelling following radiation therapy, which is evidence of inflammation that could be treated.”

The researchers believe that the early changes they see in muscle, such as swelling and leakage, might help them predict how much damage will occur in the muscles during the course of many months. By better understanding what causes these changes, clinicians will then be able to design better radiation treatments to avoid potential problems or treat the injury at an earlier stage, Krasin said.