CLINICAL APPLICATIONS

Oncology Imaging

What Is Cancer?

Cancer is a complex disease and occurs when cells in the body begin to grow chaotically. Normally, cells grow, divide, and produce more cells to keep the body healthy and functioning properly. Sometimes, however, the process goes astray; cells keep dividing when new cells are not needed. Some types of cells are more prone to abnormal growth than others. The mass of extra cells forms a growth or tumor, which can be benign or malignant.

Benign tumors are not cancer. They often can be removed and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body. More importantly, benign tumors are rarely life threatening.

Malignant tumors are cancer. Cells in malignant tumors are abnormal and divide without control or order. These cancer cells can invade and destroy the tissue around them. In a process called metastasis, cancerous cells break away from the organs on which they are growing and travel to other parts of the body, where they continue to grow. Cells from cancerous ovaries, for example, commonly spread to the abdomen and nearby internal organs. Eventually, they travel throughout the body by invading the two systems of vessels that bathe and feed all of the body’s organs; the bloodstream and lymph system.

PET/CT & Cancer

Positron emission tomography (PET) and computed tomography (CT) imaging have become essential diagnostic tools physicians use to reveal the presence and severity of cancers. PET/CT imaging helps physicians detect cancer, evaluate the extent of disease, select the most appropriate treatments, determine if the therapy is working, and detect any recurrent tumors.

Before a PET/CT scan, the patient receives an intravenous injection of radioactive glucose. Many cancer cells are highly metabolic and rapidly synthesize the radioactive glucose. Information regarding the location of abnormal levels of radioactive glucose obtained from the whole-body PET/CT scan helps physicians effectively pinpoint the source of cancer and detect whether cancer is isolated to one specific area or has spread to other organs.

From this information physicians can plan an effective treatment strategy. Treatment options include surgery, radiation therapy, systemic therapy, or a combination therapy where one or more of these options are combined.

During the course of treatment, the information from the PET/CT scan allows physicians to monitor the effectiveness of cancer therapies and provides physicians with the opportunity to change the treatment strategy if it is not working, avoiding the cost and discomfort of ineffective therapeutic procedures.

After completing the treatment regimen, a follow-up whole-body PET/CT scan can provide information to assess if the treatment was successful and if areas that were previously abnormally metabolically active have responded. Often, scar tissue at the site of surgical resection or radiation treatment may appear as an abnormality on the CT scan. The PET portion of the PET/CT scan can detect residual disease within the scar tissue and indicate if the treatment was successful or if the tumor has returned.

PET/CT scans provide information to help physicians:

  • Locate the site of the cancer
  • Determine the size of the tumor
  • Differentiate benign from malignant growths
  • Discover if the cancer has spread
  • Select treatments that are likely to be appropriate
  • Monitor the success of therapy
  • Detect any recurrent tumors

Disease-Specific Information

Bone Imaging

A PET/CT scan with sodium fluoride F 18 injection (18F NaF) is a nuclear imaging test that scans the entire skeletal system and produces high-resolution images of the bones. These images are used to detect areas of abnormal bone growth associated with tumors.

A bone scan is an important tool for detecting cancer that has metastasized or spread to the bone from a tumor that started in a different organ, such as the breast or prostate.

Some of the most prevalent cancers in the United States are commonly associated with metastatic bone disease. This is of particular clinical importance in breast and prostate cancers because of the prevalence of these diseases. At postmortem examination, 70% of breast and prostate cancer patients had evidence of metastatic bone disease.1 However, bone metastases are not restricted to only these two cancers. They may complicate a wide range of other malignancies, resulting in considerable morbidity and complex demands on health care resources. Carcinomas of the thyroid, kidney, and lung also commonly give rise to bone metastases, with an incidence at postmortem examination of 30% to 40%.

18F NaF bone imaging provides the physician with physiologic information of the bone. Live adult bone is not a rigid inorganic framework. At millions of microscopic sites throughout the skeleton, and especially at areas of disease, bone is constantly being broken down and then remade in a cellular process termed remodeling. When the PET scan shows areas of increased uptake of 18F NaF in the skeleton, it reflects sites of increased blood flow and bone remodeling. This information can be used by physicians to diagnose bone disease, detect bone injury or determine the extent of metastatic disease.

A bone PET/CT scan’s high-resolution images and its ability to scan the entire skeleton make it very helpful in detecting areas of abnormal bone growth associated with tumors. The test poses no greater risk than do conventional x-ray procedures, as the radiopharmaceutical used produces very little radiation exposure.

Effective February 2011, the Centers for Medicare and Medicaid (CMS) began covering 18F NaF PET scans as part of the National Oncologic PET Registry (NOPR).

References:
Galasko C. The anatomy and pathways of skeletal metastases. In: Weiss L, Gilbert A, editors. Bone metastases. Boston: GK Hall; 1981. p. 49 – 63.

Disease-Specific Information