Dec. 13, 2001 COLUMBUS, Ohio - Directing high-level doses of radiation at malignant tumors during surgery shows promise in treating certain childhood cancers.
Eleven of 13 children in an Ohio State University study remained cancer-free an average of four years after treatment with a technique called intraoperative high-dose-rate brachytherapy (IO-HDRBT). Ten of the surviving children were treated during advanced stages of their diseases.
"Most of the children in the study likely would have died if we hadn't used this treatment," said Subir Nag, chief of brachytherapy and professor of clinical radiology at the Comprehensive Cancer Center - James Cancer Hospital and Solove Research Institute at Ohio State.
IO-HDRBT delivers a one-time dose of radiation directly to tumors in hard-to-reach areas of the body, such as the base of the skull and the sides of the pelvis and the abdomen. It's especially useful in treating children, whose small size can sometimes prevent surgeons from using other methods to completely remove tumors.
The research appears in a recent issue of the International Journal of Radiation Oncology, Biology, Physics.
Nag and his colleagues treated and followed 13 children, ages 2 to 14, during a seven-year period. Each child had cancer of a soft tissue, such as rhabdomyosarcoma (a cancer of the muscle) and chondrosarcoma (a cancer of the cartilage). All children were treated with IO-HDRBT in conjunction with radicalsurgery, chemotherapy and external beam radiation therapy (a treatment that targets the tumor through layers of healthy, normal tissue).
"A single dose of high-dose radiation isn't enough to eradicate the disease," Nag said. But applying the one-time high dose of radiation right at the site of the tumor reduces the dose of radiation to healthy tissues. Conventional external beam radiation therapy, while necessary for treating most pediatric tumors, can cause unwanted side effects in tissues near the tumor - often resulting in growth deformities.
"It hampers bone formation, for one thing," Nag said. "We try to avoid or minimize using external radiation in children as much as possible. But avoiding it sometimes means that the tumor returns. "Brachytherapy lets us apply radiation directly to the tumor site, in turn giving them more control over the area. As a result, lower levels of external radiation and other cancer-fighting treatments need to be used."
After removing the bulk of the tumor through surgery, IO-HDRBT lets physicians apply radiation via a catheter to the tumor site. The radiation treatment itself lasts 15 to 20 minutes. The catheter is then removed and the wound is stitched. Healthy tissues surrounding the tumor are temporarily moved an inch or two away from the tumor during the radiation treatment in order to reduce the exposure of these tissues to the radiation.
"We can move bone, nerves and even bowel tissue out of the way," Nag said.
The highest recommended dose of external beam radiation therapy for treating soft tissue cancers is 41.4 Gy - radiation is measured in units called the Gray equivalent, or Gy.
"If we had used these guidelines, most of the threshold doses for normal tissue exposure in children would have been exceeded if the entire treatment had been delivered using external beam radiation therapy," Nag said. "While external beam radiation is needed to fight tumors, it can cause growth retardation or adversely affect organ function in children."
He and his colleagues were able to limit external beam radiation therapy to less than 30 Gy in most cases by using IO-HDRBT.
IO-HDRBT is best used on the hard-to-reach areas inside the body - narrow cavities and corners and curves that are difficult to treat with other treatment methods.
A technique comparable to IO-HDRBT, simply called high-dose-rate brachytherapy, involves leaving the catheter in place on the tumor for up to a week. In these cases, the tumor is usually very small, as is the radiation risk to surrounding tissues. Typically there is no need for additional treatments.
"Some patients don't fit the criteria for high-dose radiation brachytherapy," Nag said. "Leaving the catheter in for an extended time period is very difficult in young children. The intraoperative technique allows us to be more precise in directing exactly where the radiation goes without having to leave catheters in place."
Nag conducted the study with Douglas Tippin of the James Cancer Hospital at Ohio State and Frederick Ruymann of Children's Hospital in Columbus and the Comprehensive Cancer Center at Ohio State.
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