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Radiation Therapy

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what is radiation therapy?

The most common type of radiation therapy, called external beam radiation therapy is a form of cancer treatment in which ionizing radiation (in the form of electrons or protons) is directed at a cancer to impair the cancer’s ability to survive. Radiation therapy treatment for head and neck cancers is usually administered once or sometimes twice daily over several weeks, Monday through Friday. Each treatment may take only a few minutes. The ionizing radiation is directed at the carefully defined three dimensional cancer target by multiple beams. Tissue in the path of these beams incur damage to DNA. The DNA damage incurred by a cancer is generally greater than that of non-cancerous tissue. An additional method of sparing normal tissues (such as skin or organs which radiation must pass through to treat the tumor), is to use shaped radiation beams aimed from several angles to intersect at the tumor, providing a much larger absorbed dose there than in the surrounding healthy tissue. Besides the tumour itself, the radiation fields may also include the draining lymph nodes if necessary. The high dose radiation field extends around the cancer to include a margin of normal tissue to allow for uncertainties in daily set-up and internal tumor motion. These uncertainties can be caused by internal movement (for example, swelling or swallowing motion) and movement of external skin marks relative to the tumor position.

Other types of radiation therapy include temporary implants of radioactive material into the cancer (called brachytherapy) and oral administration of a radioactive medicine (such as radioactive iodine used to treat thyroid cancer).

Radiation therapy is administered under the care of a Radiation Oncologist, and in the case of radioactive iodine, sometimes by a Medical Oncologist. Note that there are some benign conditions treated with radiation therapy as well.

• National Cancer Institute’s brochure on radiation therapy

minimizing side effects of radiation therapy to the head or neck

The side effects with greatest long-term consequence for head and neck radiation involve the swallowing mechanism, saliva production, dental decay, and loss of range of motion of the jaw and neck. Minimizing major long-term side effects on tissue mobility requires active, effortful, and deliberate movement by the patient during and after the course of radiation therapy. It comes down to “use it or lose it.” Tissue forms scar after injury, including the injury from radiation dose passing through normal tissue on the way to the cancer target. Starting some weeks after radiation begins, and continuing months after radiation ends, stiff scar tissue (fibrosis) gradually develops in tissues exposed to radiation. The tongue, throat muscles, jaw joint, and neck muscles are all potentially susceptible to slowly, insidiously losing their mobility and pliability. A throat that cannot contract and relax muscles to transport food to the esophagus will not swallow effectively or safely. A jaw joint that gets stiff will lead to lock jaw (trismus). And a neck that freezes up prevents normal head turning and posture. Avoiding these problems with immobile muscles requires frequent intentional movement during and after the course of radiation to maintain pliability and avoid long-term loss of function. Involving a speech pathologist for instruction on specific exercises to perform to maintain swallow ability and jaw movement helps greatly. Placement of a gastric feeding tube through the abdominal wall is a common consideration. Neck range of motion may also benefit from a physical therapist’s instruction. During and after radiation therapy, a patient has fatigue and a sore throat and often wishes to simply rest to recover. This is a mistake! Active, effortful, diligent movement exercises, including swallowing frequently despite the pain, is essential to avoid long-term problems.

Dental preparation for radiation therapy

If the target cancer is near the mouth, it is essential for the patient to have their teeth evaluated and possibly treated by a dentist specifically for the purpose radiation therapy before starting radiation. The reason for this is that radiation accelerates dental decay and decreases the blood flow and healing ability of the jaws and teeth. If a tooth is anything less than healthy, radiation to this tooth will likely cause the tooth to develop decay, fracture, and die. This is called osteoradionecrosis. Pulling the tooth may be necessary, but after radiation, a tooth socket will not heal well, and the bone may remain exposed. This bone, which heals poorly from the effects of radiation, then can become infected, die, and then fracture. This situation may require significant undertakings of surgery and hyperbaric oxygen, antibiotics and other medicines in an attempt to heal the jaw. It is far safer to have any teeth requiring fillings or extraction to be done prior to radiation therapy. Since it takes about two weeks after any tooth extraction for the normal tooth socket to heal over, seeing a dentist and arranging any needed work must be done as expediently as possible once radiation therapy is chosen.

Lymphedema

Lymphedema is the condition of swelling (edema) of tissue relating to insufficient clearance by the lymphatic system. It can occur after treatment, either surgical, radiation, or both. New drainage pathways develop over time, but treatments such as manual lymphatic drainage performed by a physical therapist or a home-use device speed up and improve clearance of lymphedema. When severe and untreated, lymphedema can constrain movement, which can allow scar tissue to develop and limit movement permanently.

• Link to an article explaining lymphedema and its treatment from the American Head and Neck Society website.

Hypothyroidism

Hypothyroidism may occur after radiation exposure to the thyroid. For radiation fields that include the thyroid, which is the case for the treatment of many head and neck cancers, monitoring for hypothyroidism is undertaken. The time frame in which hypothyroidism may occur is three years after the completion of radiation. If hypothyroidism sets in, treatment involves use of thyroid hormone, which is available in pill form.

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