Radiopharmaceuticals

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Radiopharmaceuticals

Definition

Radiopharmaceuticals are radioactive substances that may be used to treat cancer.

Purpose

The common radiopharmaceuticals that are used in cancer treatment include:

Chromic phosphate P 32 for the treatment of lung, ovarian, uterine, and prostate cancers
Sodium iodide I 131 for treating certain types of thyroid cancer
Strontium chloride Sr 89 for treating cancerous bone tissue
Samarium Sm 153 lexidronam for treating cancerous bone tissue
Sodium phosphate P 32 for treating cancerous bone tissue and other types of cancers.

Description

Radiopharmaceuticals used in cancer treatment are small, simple substances, containing a radioactive isotope or form of an element. They are targeted to specific areas of the body where cancer is present. Radiation emitted from the isotope kills cancer cells. These isotopes have short half-lives, meaning that most of the radiation is gone within a few days or weeks.

Chromic phosphate P 32 and sodium iodide I 131

Chromic phosphate P 32 is a salt of chromium and phosphoric acid, containing a radioactive form of the element phosphorous, 32 P. Its brand name is Phosphocol P 32. Chromic phosphate P 32 is used to treat fluid accumulations that can result from lung, ovarian, or uterine cancers. It is 50-80% effective in stopping fluid leakage from these organs. Chromic phosphate P 32 also is used to kill cancer cells that remain following surgery for uterine cancer. It may be used to treat ovarian or prostate cancers directly. The use of chromic phosphate P 32 is not combined with external beam radiation, but may be used in conjunction with chemotherapy .

Sodium iodide I 131, also called radioactive iodine or radioiodide, is a salt of sodium and a radioactive form of the element iodine, 131 I. Sodium iodide I 131 is taken up by the thyroid gland, which absorbs most of the iodine in the body. Sodium iodide I 131 can destroy the thyroid gland, with only minor effects on other parts of the body. It is used following surgery for thyroid cancer to destroy any remaining cancerous thyroid tissue, or to destroy thyroid cancer that has spread (metastasized) to lymph nodes or other tissues. Sodium iodide I 131 is a standard treatment for differentiated thyroid cancer that has spread to the neck and other parts of the body. Its use improves the survival rate for such patients. It is not clear whether radioiodide is beneficial for small cancers of the thyroid that have not metastasized to other tissues.

Bone metastasis

Several radiopharmaceuticals are used to treat cancerous tissue in the bone, particularly from prostate cancer . Most prostate cancer metastasizes to the bone and often this is the cause of death. When injected into a vein these radiopharmaceuticals accumulate in cancerous bone tissue and give off radiation that kills cancer cells and relieves pain in the majority of patients. These treatments are most effective for cancer that has metastasized to multiple bones. Sometimes these radiopharmaceuticals are used in conjunction with external beam radiation that is directed at the most painful areas.

Strontium chloride Sr 89 (strontium-89) is the most common radiopharmaceutical for treating bone cancer or prostate cancer that has metastasized to the bone. It is a salt of chlorine and a radioactive isotope of strontium, 89 Sr. Its brand name is Metastron. Men with advanced prostate cancer who are responding to chemotherapy appear to have a better chance of survival if bone metastases is treated with strontium-89 every six weeks in conjunction with a chemotherapy drug.

Samarium SM 153 lexidronam is a radioactive form of samarium, 153 Sm. The element is inside a small molecule called lexidronam. The brand name for samarium SM 153 lexidronam is Quadramet. It is used primarily to treat prostate cancer that has metastasized to the bone.

Sodium phosphate P 32 is a salt of sodium and phosphoric acid containing a radioactive form of the element phosphorous, 32 P. It is used primarily for breast and prostate cancers that have metastasized to the bone. It also may be used to treat other types of cancer.

Two other radioactive isotopes, rhenium 86 and rhenium 188, sometimes are used to treat bone metastasis from prostate cancer.

Recommended dosage

Dosages of radiopharmaceuticals vary with the individual and the type of treatment. Dosages of radioactive materials are expressed in units called millicuries.

Chromic phosphate P 32 is a suspension that is delivered through a catheter, or tube, inserted into the sac surrounding the lungs, or into the abdominal or pelvic cavities. The usual dosage is 15-20 millicuries for abdominal administration and 10 millicuries for administration to the lung sac. Chromic phosphate P 32 also may be injected into the ovaries or prostate.

Sodium Iodide I 131 is taken by mouth as a capsule or a solution. The usual dose for treating thyroid cancer is 30-200 millicuries, depending on age and body size. Doses may be repeated. Treatment usually requires two to three days of hospitalization. For this therapy to be effective there must be high levels of thyroid-stimulating hormone (TSH, or thyrotropin) in the blood. This hormone can be injected prior to treatment.

Strontium-89 is injected into a vein. The usual dosage is 4 millicuries, depending on age, body size, and blood cell counts. Repeated doses may be required.

The usual dosage of samarium Sm 153 lexidronam is 1 millicurie per kg (0.45 millicurie per lb) of body weight, injected slowly into a vein. Repeated doses may be necessary. Because samarium Sm 153 lexidronam may accumulate in the bladder, it is important to drink plenty of liquid prior to treatment and to urinate often after treatment. This reduces the irradiation of the bladder.

The dosage of sodium phosphate P 32 depends on age, body size, blood cell counts, and the type of treatment. The usual dosages range from 1-5 millicuries. Repeated doses may be required.

Precautions

Some individuals may have an allergic reaction to strontium-89, samarium SM 153 lexidronam, or sodium phosphate P 32.

Radiopharmaceuticals usually are not recommended for use during pregnancy. It is recommended that women do not become pregnant for a year after treatment with sodium iodide I 131. Breast-feeding is not possible during treatment with radiopharmaceuticals.

Precautions before treatment with sodium iodide I 131

Foods containing iodine, such as iodized salt, seafoods, cabbage, kale, or turnips, should be avoided for several weeks prior to treatment with sodium iodide I 131. The iodine in these foods will be taken up by the thyroid, thereby reducing the amount of radioiodide that can be taken up. Radiopaque agents containing iodine sometimes are used to improve imaging on an x ray . A recent x-ray exam that included such an agent may interfere with the ability of the thyroid to take up radioiodide.

Diarrhea or vomiting may cause sodium iodide I 131 to be lost from the body, resulting in less effective treatment and the risk of outside contamination. Kidney disease may prevent the excretion of radioiodide, increasing the risk of side effects from the drug.

Precautions after treatment with radiopharmaceuticals

Strontium-89, samarium Sm 153 lexidronam, and large total doses of sodium iodide I 131 may temporarily lower the number of white blood cells, which are necessary for fighting infections. The number of blood platelets (important for blood clotting) also may be lowered. Precautions for reducing the risk of infection and bleeding include:

avoiding people with infections
seeking medical help at the first sign of infection or unusual bleeding
using care when cleaning teeth
avoiding touching the eyes or inside of the nose
avoiding cuts and injuries

It is important to drink plenty of liquids and to urinate often after treatment with sodium iodide I 131. This flushes the radioiodide from the body. To reduce the risk of contaminating the environment or other people, the following procedures should be followed for 48-96 hours after treatment is sodium iodide I 131:

avoiding kissing and sex
avoiding the handling of another person's eating utensils, etc.
avoiding close contact with others, especially pregnant women
washing the tub and sink after each use
washing hands after using or cleaning the toilet
using separate washcloths and towels
washing clothes, bed linens, and dishes separately
flushing the toilet twice after each use

Strontium-89 and samarium Sm 153 lexidronam also are excreted in the urine. To prevent radioactive contamination, special measures should be followed for one week after receiving strontium-89 and for 12 hours after receiving samarium Sm 153 lexidronam:

using a toilet rather than a urinal
flushing the toilet several times after each use
wiping up and flushing any spilled urine or blood
washing hands after using or cleaning a toilet
washing soiled clothes and bed linens separately from other laundry

Individuals with bladder control problems must take special measures following treatment to prevent contamination with radioactive urine.

Side effects

The more common side effects of chromic phosphate P 32 may include:

loss of appetite (anorexia )
abdominal cramps
diarrhea
nausea and vomiting
weakness or fatigue

Less common but serious side effects of chromic phosphate P 32 may include:

severe abdominal pain
severe nausea and vomiting
fever
chills
dry cough
sore throat
chest pain
difficulty breathing
bleeding or bruising

Side effects of treatment with sodium iodide I 131 are rare and temporary. However, they may include:

loss of taste
dry mouth (xerostomia )
stomach irritation
nausea and vomiting
tenderness in the salivary glands or neck

Large total doses of radioiodine may cause infertility in men.

Flushing and transient increased bone pain are among the more common side effects of strontium-89.

Less common side effects of samarium Sm 153 lexidronam include:

irregular heartbeat
temporary increase in bone pain
nausea and vomiting

Signs of infection due to low white blood cell counts after treatment with strontium-89, samarium Sm 153 lexidronam, or sodium iodide I 131 include:

fever or chills
cough or hoarseness
lower back or side pain
painful or difficult urination

Signs of low platelet count after treatment with strontium-89, samarium Sm 153 lexidronam, or sodium iodide I 131 include:

bleeding or bruising
black, tar-like stools
blood in urine or stools
tiny red spots on the skin

Side effects are rare with sodium phosphate P 32. However, for patients treated with sodium phosphate P 32 for bone pain, side effects may include:

diarrhea
fever
nausea and vomiting

Anemia (low red blood cell count) or a decrease in the white blood cell count also are possible.

Since children and older adults are particularly sensitive to radiation, they may experience more side effects during and after treatment with radiopharmaceuticals.

Interactions

Radiation therapy or anticancer drugs may increase the harmful effects of strontium-89 and samarium SM 153 lexidronam on the bone marrow. Medicines containing calcium may prevent strontium-89 from being taken up by bone tissue. Etidronate (Didronel, one of the so-called bisphosphonates that may be used to prevent or treat osteoporosis) may prevent samarium Sm 153 lexidronam from working effectively.

Margaret Alic, Ph.D.