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The precision era of radiation therapy

August 01, 2005|by Dr. Dan Cornell

Following the discovery of X-rays more than 100 years ago, it was determined that X-rays could be used to cure certain forms of cancer. However, initial attempts at directing radiation at the tumor were hampered because the radiation beam did not have enough energy to penetrate to deeper structures, such as the prostate.

Another problem with early treatments was an inability to focus the beam to avoid critical organs that might be close to the tumor region. It was understood that if radiation were given in small, daily doses, it had the ability to shrink tumors and allow normal tissues to recover from the insult of the small doses.

On the other hand, a single large dose would cause tumors to shrink, but the side effects on normal tissue were severe.

Radiation therapy became the treatment of choice for various cancers because it could eliminate tumor cells that were hiding in the middle of a normal organ. For example, a small cancer involving the vocal cords could be eradicated without harming the delicate structures of the voice box. Radiation allowed the voice to be preserved, while surgically removing the tumor often destroyed the ability to produce normal speech.

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Certain tumors were beyond the reach of radiation. Some of the tumors couldn't be seen on X-rays and some were located too close to a critical organ to allow a full dose of radiation. Within the last 10 years, radiation treatments have undergone a dramatic change. The penetrating ability of radiation was increased years ago, but information as to the exact position of the tumor was lacking. The real advance in radiation treatment is related to new imaging methods such as positron emission tomography (PET), magnetic resonance imaging (MRI), and high resolution computed axial tomography scans (CT scans). In addition, more sophisticated computers can blend several different imaging studies to create a very accurate map of where the tumor is located and where it might have spread. This accurate mapping allows radiation therapy to be directed with great precision.

In the past, radiation was directed to cover the tumor and a region around the tumor to include any microscopic spread or "tumor tentacles." The microscopic spread could be eliminated by the treatment course, but, sometimes, the bulk of the tumor was under-dosed since the exact position of radiation-sensitive normal structures, such as the spinal cord, was unknown.

Now, radiation therapy doctors can visualize the tumor and nearby critical normal organs with pinpoint accuracy. They can direct a radiation therapy beam with similar accuracy. The beam can be shaped and changed in intensity as the treatment machine slowly rotates around the patient. This intensity-modulated radiation therapy has created a quiet revolution in cancer treatment.

By using sophisticated computers, radiation therapy doctors and their staff can designate exactly where to apply the high dose of radiation with little risk of collateral damage to surrounding structures. Recent advances in radiation therapy have opened new doors of hope for patients by curing cancers in greater proportions than ever before.




Dr. Dan Cornell is a radiation oncologist at the John R. Marsh Cancer Center at Robinwood Medical Center, east of Hagerstown.

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