The Melanoma Book
By Howard L. Kaufman, M.D., FACS
Radiation is a form of energy and radiation therapy is a treatment that includes the use of both X-rays and gamma rays to kill melanoma cells. The mechanism by which radiation kills tumor cells is not entirely understood. While it is clear that radiation damages the DNA of tumor cells, which prevents the cells from growing and dividing normally, there is evidence that radiation has other anti-tumor effects. The local delivery of radiation releases a number of reactive molecules that may interfere with normal cell growth. Radiation also damages nearby blood vessels and may cut off the blood supply to tumors. More recently there is evidence that radiation may help induce a local immune response to fight cancer cells. Although this all sounds like a good way to eliminate melanoma cells, the susceptibility of any individual melanoma cell to radiation can vary. In addition, normal cells are also sensitive to the effects of radiation and so the benefits must be weighed against the risks to normal cells.
Radiation is usually used for advanced cases of melanoma where surgical removal is not possible and chemotherapy may be hard for a patient to tolerate. Radiation therapy is the major method of treating melanoma in the brain and spinal cord. There is also new evidence emerging from research laboratories that radiation therapy combined with immunotherapy may be especially effective. Radiation therapy needs to be carefully planned in coordination with other treatment regimens. Even when it does not kill all the melanoma cells, radiation therapy is especially useful as palliative treatment for relieving pain.
For those patients who may be candidates for radiation therapy, a radiation oncologist is consulted. A radiation oncologist is trained in the use of radiation for the treatment of cancer. Many comprehensive medical centers have a department of radiation oncology where the radiation oncologist has an office and access to the necessary machines. A number of other radiation health specialists may be employed to coordinate therapy for patients.
The amount of radiation used depends on the size of the tumor, the location of the tumor, the sensitivity of the tumor and surrounding normal tissues to radiation, and the type of radiation being used. Based on these considerations, a total dose will be calculated and then divided into smaller fractions to be delivered on different days. The number of days and schedule of treatment will then be determined. The radiation oncologist meets with die patient, discusses the process involved with the selected procedure, the side effects of radiation, and the treatment schedule planned. An imaging scan, such as a CT or MRI scan is typically used to locate the exact position of the tumor in the body. The body is often marked with a pen or similar device so that the tumor can be located during each radiation treatment visit.
Radiation may be delivered from an external source or from a source implanted inside the body. External beam therapy refers to radiation from an energy source outside of the body and uses a beam to direct the radiation to the tumor. The treatment usually lasts only a few minutes at a time. Stereotactic radiosurgery allows more accurate tumor targeting so that higher doses of radiation can be delivered while limiting the amount of damage to surrounding normal tissues. The procedure uses several powerful radiation beams at various angles that focus precisely on the tumor. Gamma knife radiosurgery is a specialized form of stereotactic radiosurgery and is especially helpful for the treatment of melanoma that has spread to the brain. The gamma knife technique is a non-invasive procedure that locates the melanoma by CT or MRI scan before the procedure. A lightweight frame is placed on the head using a local anesthetic before the MRI/CT scan. The radiation oncologist can localize the tumor site exactly and uses the head frame to precisely pinpoint the location of the melanoma. The "knife" is composed of 201 intersecting beams of radiation, resulting in a highly concentrated dose of radiation at the tumor site while avoiding normal brain tissue. It's similar to using a magnifying glass to concentrate the powerful rays of the sun in a single area. The procedure is completed on one visit but may require medication to prevent brain swelling and seizures. Gamma knife radiosurgery may be as effective as open surgical procedures, although it is best used on small melanoma lesions. In fact, some reports suggest that fewer than 10 percent of patients who have gamma knife radiosurgery have evidence of brain melanoma at the time of death.
Internal radiation therapy, also referred to as brachytherapy, is a procedure whereby radioactive material is placed inside the body to release the radiation at the site of a tumor. This approach, commonly used to treat prostate cancer, has not been as useful for melanoma. The high doses of radiation can damage normal cells if they are exposed to the radiation beam, which can lead to serious side effects. The most common side effect of radiation is fatigue, although other side effects depend on the exposure of normal tissues in the area of the radiation dose. It usually takes some recovery time after radiation treatments to feel better.