Study at Fox Chase Cancer Center Provides Guidelines For Optimal Dose of Spinal Radiation to Avoid Side Effects
PHILADELPHIA (November 1, 1999) -- "Spinal cord injury is the most feared side effect of radiation therapy," said Timothy E. Schultheiss, Ph.D., director of radiation physics at Fox Chase Cancer Center. "To avoid this problem, physicians have been overly conservative with radiation doses that may affect the spine during treatment for head and neck or lung cancer."
Careful treatment planning, such as the three-dimensional imaging techniques used at Fox Chase, helps tailor the radiation beam to the tumor and thus protect normal tissues, Schultheiss pointed out. However, even with careful shielding, radiation oncologists have tended to err on the side of caution, so patients may not receive the optimal dose of radiation to cure or control their cancer, he explained.
Now a statistical analysis by Schultheiss provides guidelines for optimal radiation doses that still avoid spinal cord damage (known as myelopathy). The results will be presented today at the American Society for Therapeutic Radiology and Oncology (ASTRO) conference in San Antonio, Texas.
"What this will do for the treatment of certain cancers is to allow physicians to increase doses to the tumor," Schultheiss said.
Although extremely rare, spinal cord damage may result from radiation treatments to help cure some tumors of the head and neck, where the cervical spinal cord (starting at the neck) is exposed to the radiation beam. Radiation therapy for people with lung cancer exposes the thoracic spinal cord (behind the chest) to possible injury.
If the spine is injured, the resulting damage to nerves may affect range of motion, alter the way a person walks or lead to paralysis. Symptoms may not develop for months or even years after the treatment.
"I've put considerable effort into the study of optimal dosage," said Schultheiss. "Where exposing the spine to radiation is an issue, we felt we should be able to estimate the highest-tolerated dose that doesn't result in injury."
Because the problem is rare, no single institution has had enough clinical data to analyze the doses involved. Compiling data from six published sources, Schultheiss set out to establish the radiation dose response of the cervical spinal cord and also to analyze dose-response data on the thoracic cord. Traditionally, physicians have considered the thoracic spinal cord even more sensitive to the effects of radiation than the cervical cord.
The results of this meta-analysis produced a mathematical dose-response function for the cervical cord. Measured in units of absorbed radiation energy, Gy, the dose-response curve showed tolerated doses ranging from 45 to 57 Gy, with 0.1 to 1 percent chance of spinal injury.
"It was not possible to obtain a smooth dose-response curve for the thoracic spinal cord data," Schultheiss noted. "However, it is clear from the graphical analysis that the response of the thoracic cord is different from and less than the cervical cord.
"The evidence suggests that the thoracic cord is less sensitive to radiation than the cervical cord. The previous belief that the thoracic cord is more sensitive cannot be substantiated."
This Fox Chase analysis "reasonably well defines the risk of spinal cord injury," Schultheiss said. Especially for patients with lung cancer, who are the most likely to receive radiation therapy that exposes the spine to the radiation beam, this means that physicians in the future will be able to prescribe higher, more effective doses that may better control the cancer or relieve symptoms.
Fox Chase Cancer Center is one of 36 National Cancer Institute-designated comprehensive cancer centers in the nation. The Center's activities include basic and clinical research, prevention, detection and treatment of cancer and community outreach programs.
Fox Chase Cancer Center, part of Temple University Health System, is one of the leading cancer research and treatment centers in the United States. Founded in 1904 in Philadelphia as one of the nation’s first cancer hospitals, Fox Chase also was among the first institutions to receive the National Cancer Institute’s prestigious comprehensive cancer center designation in 1974. Fox Chase researchers have won the highest awards in their fields, including two Nobel Prizes. Fox Chase physicians are routinely recognized in national rankings, and the Center’s nursing program has achieved Magnet status for excellence three consecutive times. Fox Chase conducts a broad array of nationally competitive basic, translational, and clinical research and oversees programs in cancer prevention, detection, survivorship, and community outreach. For more information, call 1-888-FOX-CHASE (1-888-369-2427).