What are bone scans? How do they help detect cancer?

Cancers diagnosed: Cancers that have spread to the bone (metastatic cancers), primarily breast, prostate, and lung cancers, and kidney and thyroid cancers to a lesser degree

Why performed: Cancer cells can spread from their primary location to the bone in a multistep process known as metastasis. Metastatic bone disease can result in bone pain and an overall decrease in the quality of life. Tumor cells residing in the bone can also cause bone destruction (known as resorption) as a result of both direct effects of the tumor and the activation of osteoclasts (a type of bone cell responsible for resorption). This process may result in weakened bones and a greater risk of bone fractures. Furthermore, calcium may be released from the bone as it breaks down, and elevated levels of calcium in the blood can cause loss of appetite, nausea, and exhaustion and can affect the heart and kidneys.

A bone scan is one method to detect if cancer has spread to the bone and to identify where the cancer is located. Bone scans can also be used to determine the stage of disease, as well as to examine how much bone damage is present. Additionally, bone scans may be performed to monitor the response to treatment, as some cases of bone cancers are treated with drugs such as bisphosphonates in order to reduce bone resorption.

Patient preparation: Very little prior preparation is required, and patients do not need to fast. At the time of the scan, patients must remove all metal objects (such as jewelry, zippers, and metal buttons), as they may interfere with the scan. In some cases, the clothes should be removed and the patients will wear a hospital gown.

Steps of the procedure: A bone scan will usually be performed in a hospital. The two stages of this procedure are the tracer injection and the scan.

A radioactive tracer will be injected into a vein in the patient’s arm. Patients will then wait one to four hours to allow the tracer to be incorporated into the bone tissue. Drinking several glasses of water (at least four) will help to eliminate excess tracer through the urine. Patients will be instructed to empty the bladder before the scan begins.

For the scan, patients must lie still on a table while the scanning camera moves overhead and scans the body. The camera will detect the gamma rays emitted by the tracer that has concentrated in the bone. Sometimes the scans will be conducted when patients are in different positions in order to view the bones from various angles. On average, the bone scan lasts about thirty to sixty minutes.

After the procedure: Care should be taken when sitting up at the completion of the scan, as dizziness or light-headedness may result from the extended period of lying down. Patients will be instructed to drink plenty of fluids for at least forty-eight hours after the bone scan to help eliminate the remaining radioactive tracer. Patients who are breastfeeding should also discard their breast milk for the first two days after the procedure.

Risks: Common risks include redness, soreness, or swelling at the injection site. In rare cases, patients have allergic reactions to the tracer.

Results: If the radioactive tracer is distributed equally throughout the bones, then the result will be considered normal. An abnormal result will occur when the tracer concentrates in distinct sites of the bone, resulting in “hot spots.” Hot spots indicate that there is a lot of activity in the bone, both building and resorption, which may be a sign of tumor cells within the bone. Hot spots, however, may also be caused by a fracture or bone infection. Therefore, if hot spots are detected, the doctor will often suggest blood tests, biopsies, or other imaging tests in order to confirm the presence of cancer.

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