Q: My mom’s doctor recommended radiation therapy for her cancer. Is this safe?

A: Over a century ago, soon after X-rays were discovered in 1895, radiation therapy was first used to treat cancer. Since that time there have been huge developments in this treatment modality, and radiation therapy is now used as treatment, most often as a supplement surgery, chemotherapy and other cancer treatments, for about 50 percent of all cancer patients.

Radiation therapy uses ionizing radiation to damage the DNA of cancer cells; since they multiply rapidly this causes them to die. However, normal cells may also be affected by radiation therapy and this is the cause of the side effects and/or complications of this treatment modality (these are minimized since normal cells are better able to repair DNA damage), whether directly from the radiation effects or indirectly from swelling or other reactions. The potential for complications limits the total amount of radiation therapy that can be delivered to a patient. Examples of side effects: radiation therapy to the abdomen may cause nausea/vomiting and/or changes in bowel movements, to head/neck it may cause oral sores, to the pelvis it may cause urinary and/or reproductive issues and to the brain it may cause memory and/or cognitive issues.

Finally, normal cells adversely affected by radiation therapy may develop into cancer. For example affected white blood cells may develop into leukemia cells.

The key aspects that are considered when radiation therapy is being planned include the type and location, including depth, of the cancer, and the characteristics of the patient (their overall health, other concomitant treatments, can they lie still etc.). These factors will be put into a computer simulation which will be used by the radiation oncologist to plan the specifics of the radiation therapy, including the type and dose of radiation and how it will be administered — the amount of each specific dose, frequency and number of treatments etc.

Radiation therapy may be delivered to the patient’s tumor by ‘shining’ an energy beam into it to kill the cancer cells. This is known as external beam therapy. The most common method uses photons (gamma or X- rays, types of light that differ in frequency) produced by radioactive decay of an unstable element (such as cobalt-60) or from a linear accelerator.

Photons are used since they can penetrate the body (like x-rays do to create images). Radiation therapy with particles other than photons is also possible, but works in a slightly different way. These radiation therapies (most commonly protons, but sometimes electrons or other radiation therapies) deposit energy when they ‘slow down’ as they pass through body tissue; the depth of the cancer is critical as the specific characteristics of the treatment beam are calibrated so the radiation therapies are stopped inside the cancer. Electrons do not penetrate very deeply and so are most often used for skin or other more superficial cancers.

External radiation therapy can be administered by splitting the dose into smaller radiation therapies and focusing it on the cancer; in this way minimizing the amount of radiation that hits normal tissue en route to the cancer. Three dimensional imaging (CT or MRI) is used to define the cancer target volume that will be treated so that all the cancer receives radiation. The amount of radiation can be modulated to increase/decrease how much is administered to fine tune the treatment as well as to minimize delivery of radiation to normal tissue (called intensity-modulated radiation therapy).

Since positioning of the patient is so important (to be sure the cancer is targeted and radiation of normal tissue is minimized) the patient may be periodically re-imaged (using CT or MRI) even during the delivery of their radiation therapy.

Certain diseases require irradiation of the patient’s entire body. For example, this is done prior to bone marrow transplants which may be utilized for some types of cancers as well as for other diseases. Radiation therapy may also be administered internally inside patient (brachytherapy). This can be done by using a radioactive implant (sometimes done for prostate, gynecological or breast cancers). It can also be done by directly irradiating the area around a tumor during surgery.

Finally, a substance that binds to a cancer can be “tagged” with a radioactive substance, thereby irradiating the cancer cells. For example, a radioactive form of iodine may be administered intravenously to a patient with thyroid cancer; thyroid tissue absorbs iodine). There are also antibodies to certain cancers that can have radioactive molecules linked to them (binding to the cancer to deliver the irradiation).

No medical treatment is without risk, but when the potential benefits of radiation therapy outweigh the risks this modality will often be recommended, whether as primary treatment or as supplement to other treatments. This is done to improve the patient’s outcome, whether as an attempt to eradicate their disease completely or as palliation to improve the quality and quantity of their days.

Jeff Hersh, Ph.D, M.D., can be reached at drhersh@juno.com.