SAN FRANCISCO - A technology developed for cruise missiles can enable doctors to catch tumors in a crossfire of radiation beams, a researcher said Monday.
The technique, for aiming the beams with great precision, should let doctors use crossfire therapy to tackle tumors anywhere in the body rather than just the brain, said Dr. John R. Adler Jr. of the Stanford University Medical Center.
The therapy would replace many operations with a painless outpatient procedure.
Crossfire therapy has become standard for treating brain tumors. In the procedure, doctors attach a metal frame to the skull with screws to hold the head still and help aim the beams. The beams are fired from hundreds of points, following paths that intersect only at the tumor. Working together, they kill the tumor while sparing other tissue.
Doctors have wanted to use crossfire therapy to treat tumors elsewhere in the body, but screwed-in frames won't work below the head, Adler said at a seminar sponsored by the American Cancer Society.
Adler and his colleagues adapted the cruise missile navigation technique to do for the rest of the body what the frame does for the brain.
But the new technique can also be used to replace the frame and improve crossfire therapy for brain tumors, he said. It involves comparing what the missile "sees" while flying with stored images of what it should be seeing if it's on course.
For treating brain tumors, the researchers make a three-dimensional X-ray image of the patient's skull and tell a computer where the tumor is in relation to the skull.
Then they let the computer generate hundreds of alternative images that show what the skull would look like if it moved a little in various directions. In each alternative image the computer also calculates where the tumor would be.
Then, during therapy, the computer compares X-ray images of the skull at various moments with the alternatives in memory. When a match is found, the computer can note the associated tumor location and aim the next radiation shot accordingly.
The radiation beams are fired from a robot arm.
But when used for tumors outside the brain, the computer would locate the tumor in relation to skeletal landmarks or implanted gold seeds rather than the skull, Adler said.
The technique has been tried on eight patients with malignant brain tumors, and it has worked as well as the conventional approach with the screwed-in frame, Adler said.
Two other patients, with benign tumors in the spinal cord, have also been treated and are being studied, he said. One patient has shown no enlargement of the tumor or progression of paralysis over eight months of observation, he said. The other patient was treated only three months ago, and so follow-up information is not yet available, Adler said.
Researchers are now planning studies to try the technique on head and neck cancers, prostate and pancreas cancers and cancers that have spread to the lung and liver from elsewhere, he said.
The method might be particularly useful for treating small tumors in the livers of patients who can't handle much radiation elsewhere in the organ and aren't good candidates for surgery, said medical oncologist Dr. Judith Luce of San Francisco General Hospital and the University of California at San Francisco.
It would also be helpful for treating head and neck cancers, she said, because surgery can be disfiguring and conventional radiation produces harmful side effects. These can include dry mouth, which promotes cavities and tooth loss, as well as bone death.