Patients receiving radiation therapy are understandably apprehensive, especially if they do not know what to expect. The precise course of treatment varies from patient to patient and depends upon many factors, including the type of cancer, its site and stage, the general condition of patient and other considerations. The total radiation dose and timing of the treatments are carefully calculated and, as stressed earlier, the radiation must be accurately beamed to the cancer with as little exposure as possible to healthy tissues. Modem X-ray and other radiation therapy machines are designed to achieve this goal. In addition, special restraints and other mechanical devices are used to keep the patient absolutely still during a treatment session. These gentle but firm restraining devices are made of lucite, plaster, lead and other materials. They may be fashioned for each patient individually, or adjusted as needed in the mold shop that is an integral part of every radiation therapy department.
Lead shields are particularly important in protecting healthy tissue because they act as a barrier to X rays. Lead does not completely block the radiation, but—depending upon the thickness of the lead and energy of the X-ray beam—the dosage can be reduced to less than one percent of its original level, resulting in a negligible exposure to normal tissues. Thus radiation therapy can be given to the lymph nodes in the middle of the chest to treat Hodgkin’s disease, for example, while the sensitive surrounding lung tissue is protected from the high-dose radiation by precise lead forms made to match the patient’s lungs. In general, muscle and nerve tissues are the most resistant to radiation injury, followed by the skin. The intestines, kidneys, and bone marrow are particularly sensitive; in fact, the sensitivity of the kidneys and gastrointestinal tract greatly restricts the use of generalized radiation therapy for abdominal cancer.
Although external beam radiation is most commonly used, a number of relatively new alternative means of delivering radiation have been developed. Increasing use is being made of materials made radioactive by cyclotron radiation that are then implanted directly into the tumor or very close to it. This technique, called brachy therapy, is constantly being refined. It is now used either alone or in addition to the external beam. Typically, the radiation is administered through implanted “seeds” and wires, which may be made of gold or an even rarer element, indium. The radiation from these seeds does not penetrate for more than a third of an inch of tissue, meaning that the implants must be carefully and closely spaced to expose all of the tumor to intense curative doses. In this way the cancer is exposed to continuous radiation, albeit at lower levels of intensity usually amounting to only about 30 to 50 rads per hour. These radioactive seeds may be implanted directly into the cancer, as in treating prostate cancer in men, or may be implanted in a hollow organ space (intracavitary), as in the treatment of cancer of the uterus.
CT scans and ultrasonography make it possible to place these seeds and wires with accuracy. Special molds to hold the radioactive seeds in place may be required for those inserted into hollow spaces, particularly when the spaces are irregularly shaped, such as the nose or ear canals. Some implants are permanent for example, those used to treat some kinds of prostatic cancer. Others may be left in place for a few days or weeks, and still others deliver precise dosages that require the patient to wear the mold for specific time periods. A nasal mold holding radioactive seeds, for example, may be worn for three hours and seventeen minutes on eight consecutive days. Accuracy in determining the amount of radiation needed to destroy all cancer cells is vital, because it is the last 10 or 15 percent of the radiation that kills the last remaining cancer cells, thereby preventing recurrence.