As a result of technical advances and training programs, radiation oncology has developed into a highly refined specialty. Now, with superb accuracy, a radiation beam can be focused on the tumor without damaging surrounding normal tissue. Linear accelerators, which hit tumors with up to 40 million electron volts, many times the dose of earlier machines, provide deeper penetration and a more precise beam that does less damage to healthy cells. By itself, as well as in combination with other therapies, radiation therapy is an increasingly potent tool.
Radiation therapy, in contrast to what many people
imagine, does not destroy or dissolve cancer cells like a laser beam would.
Possibly, if the dose were multiplied many, many times, it would. However,
it is given in such small doses that its prime mission is to damage the
DNA of a malignant cell. The cell does not die instantly, but when it tries
to divide, it is unable to and dies at that time. Therefore, radiation
treatments continue to be effective on the tumor after the treatments are
completed, often for 90 days and more. Sometimes, tumors shrink primarily
after the therapy is finished. Radiation treatments are normally given
5 days a week, not because the doctors don't like to work on the
weekends or have a strong union, but because
during the other two days, normal healthy cells will repair the damage
done to their DNA. Cancerous cells are unable to repair this damage.
Because scar tissue will continue to build up, changes could be noticed in follow up X-rays even though the tumor is gone. Also, no changes may be noticed in a bone scan for some time even though the radiation did its job because the bone mending itself after radiation will give the same image as a tumor on a scan.