Radiation

Radiation therapy is the second major cancer treatment today. One problem with this form of therapy is that it only works on a small, localized area. It does not travel through a patient. Rather it must be “focused” at the site of the tumor. Therefore, this type of treatment will not usually be effective if the tumor has spread.

Radiation works by destroying tumor cells indirectly. The radioactive particles form free radicals. These unstable molecules bind to other molecules in strange ways, causing damage, the worst of which is to the DNA.

Certain cells are more likely to be affected by radiation. Rapidly dividing cells are more vulnerable to radiation exposure. These include cancer cells, cells of the bone marrow and the intestinal tract. Patients usually receive many small doses of radiation over a longer period of time. That way normal cells have a chance to recover and repair their damaged DNA (remember, tumor cells are not so good at this). Also, the tumor will shrink a little and blood flow within it will improve. Improved blood flow allows the tumor to reoxygenate, making it more vulnerable to radiation.

Certain tumor types are resistant to radiation. These include sarcomas, melanomas and gastrointestinal tumors. For these types of tumors, other methods must be used.

As mentioned before, radiation works by killing cells indirectly. Unfortunately, radiation damages all types of cells, not just the tumor cells. Radiation causes the oxygen within a cell, to split apart and form free radicals. These free radicals damage the cell’s DNA, which is exactly the way carcinogens work (remember, radiation is a carcinogen). This may be the same mechanism as the carcinogens which initiated the tumor in the first place. Therefore, a secondary tumor may eventually form at the same site as the first tumor due to the radiation dose received in that area to the normal cells. The normal cells near the site of the tumor may become cancerous after numerous radiation treatments. Fortunately, secondary tumors do not always spring up.

In the attempt to cause less damage to normal cells, a new technology allowing oncologists to pinpoint tumors has been developed. It is hoped that in the process of zapping tumors, fewer normal cells will be hit and there will be less chance for a new tumor to form as a by-product of the therapy. The chance of completely erradicating the tumor is also increased by pinpointing the radiation.