How is Radiation Therapy Delivered?
Radiation therapy is often delivered from a source outside of the body (external-beam radiation therapy) or from radioactive material placed in the body near cancer cells (internal radiation therapy, commonly called brachytherapy). Systemic radiation therapy uses a radioactive substance, given by mouth or into a vein, that travels in the blood to tissues throughout the body.
Radiation doses for cancer treatment are measured in a unit called a Gray (Gy), which is a measure of the amount of radiation energy absorbed in tissue. Different doses of radiation are needed to kill different types of cancer cells.
Patients do not become radioactive from external beam radiation. Patients are radioactive for varying period of time from either brachytherapy or systemic therapy. Your physician and/or a radiation therapy nurse will guide you on how to manage this temporary radioactivity.
Patients who receive external-beam radiation therapy usually have to travel to hospital or an outpatient facility for 5 days a week for several weeks. Most often, one dose (a single fraction) of the total planned dose of radiation is given each day. Occasionally, two treatments a day are given, called hyperfractionation.
There are several reasons for daily fraction of radiation over several weeks:
To increase the likelihood that cancer cells are exposed to radiation when they are most vulnerable to genetic damage.
To allow oxygen to penetrate to the center of the cancer as the cancer shrinks during treatment, increasing its sensitivity to radiation.
To allow the surrounding normal cells time to repair radiation damage (which they do more efficiently than cancer cells).
In recent decades, doctors have tested whether other fractionation schedules are helpful, including:
Hyperfractionation: Smaller doses of radiation given more than once a day.
Hypofractionation: Larger doses given once a day or less often to reduce the number of treatments.
Researchers hope that these different fractionation schemes may either be more effective than traditional fractionation or be as effective but more convenient. Radiation given by brachytherapy is most commonly in the form of gamma rays, which are derived from the decay of radioactive elements. The gamma rays affect cells very similarly to X-rays.