Radiation Therapy Principles

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Radiopharmaceuticals are drugs that contain radioactive materials called radioisotopes. They may be put into a vein, taken by mouth, or placed in a body cavity. Depending on the drug and how it’s given, these materials travel to various parts of the body to treat cancer or relieve its symptoms. They put out radiation, mostly in the form of alpha and beta particles, that target the affected areas. They’re most often used in small amounts for imaging tests, but larger doses can be used to deliver radiation.

Treatment of bone pain

Strontium 89 (Metastron®), samarium 153(Quadramet®), and Radium- 223 (Xofigo®) are radiopharmaceuticals that can be used for tumors that have spread to the bones (bone metastases). Other drugs are also being studied. These medicines are given in veins (intravenously or IV), so that they go into the blood circulation. They build up in the areas of the bone where there is cancer. The radiation they give off kills cancer cells and eases the pain caused by bone metastases.

For cancer that has already spread to several bones, this approach can be better than trying to aim external beam radiation at each affected bone. These drugs may be used along with external beam radiation which is aimed at the most painful bone metastases. This combined approach has helped many men with prostate cancer, but it has not been studied as much for use in other cancers.

Some people notice more bone pain for the first couple of days after treatment, but this is not common. These drugs can also lower blood cell counts, especially white blood cells (which can increase the risk of infection) and platelets (which can raise the risk of bruising or bleeding).

Treatment of thyroid cancer

The thyroid gland absorbs nearly all of the iodine in the blood. Because of this, radioactive iodine (also known as radioiodine or iodine 131) can be used to destroy the thyroid gland and thyroid cancer with little effect on the rest of the body. This treatment is often used after thyroid cancer surgery to destroy any thyroid cells left behind. It’s also used to treat some types of thyroid cancer that spread to lymph nodes and other parts of the body. For more information, please see our document called Thyroid Cancer.

Small doses of radioiodine can be given without the patient having to be in the hospital, but the usual treatment doses for thyroid cancer require 2 to 3 days in the hospital. Several weeks after treatment, the radioiodine is gone from the body. At that point, doctors can check to see how well the treatment worked.

Short-term side effects of radioiodine treatment are rare, but may include neck tenderness, nausea and stomach irritation, tenderness of the salivary glands, and dry mouth. Large doses may cause low blood cell counts. Men may become infertile (unable to father children) after large doses.

There may be some longer-term risks, too. Large studies have found that there may be a very slight increase in the risk of developing other types of cancer, including leukemia, in the future.

It’s recommended that women of childbearing age avoid becoming pregnant during treatment and for at least a year after treatment. If a woman gets pregnant more than a year after treatment, there is no evidence of a higher risk of birth defects or miscarriage. Women treated with radioactive iodine during their childbearing years may have slightly earlier menopause.

Phosphorus 32

This form of phosphorus (also known as P-32 or chromic phosphate P 32) is put inside brain tumors that are cystic (hollow) to kill the tumor without hurting the healthy parts of the brain.

In the past, P-32 was given into a vein (as an IV) as a common treatment for a blood disease called polycythemia vera. P-32 was also placed inside the abdomen (belly) as a treatment for ovarian cancer. It’s rarely used in these ways today, because there are better drugs with fewer side effects.

Radio-labeled antibodies

Monoclonal antibodies are man-made versions of immune system proteins that attack only a specific molecular target on certain cancer cells. Scientists have learned how to pair these antibodies with radioactive atoms. When put into the bloodstream, the antibodies act as homing devices. They attach only to their target, bringing tiny packets of radiation directly to the cancer.

Radio-labeled antibodies are used to treat some non-Hodgkin lymphomas, especially those that don’t respond to other treatments. They might cause allergic reactions when first infused. They might also lower blood cell counts, which can raise the risk of infections, bruising, or bleeding.

Last Medical Review: 10/23/2013
Last Revised: 10/23/2013