Fact Sheet: Molecular Imaging and Ovarian Cancer

 

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Ovarian cancer is cancer that begins in the ovaries, the egg-producing female reproductive organs. The cause of ovarian cancer, the fifth most common cancer among women, is unknown. The National Cancer Institute estimates that in 2010, 21,880 women in the United States will be diagnosed with ovarian cancer and 13,850 women will die from the disease.

Ovarian cancer is highly curable when treated at an early stage. However, because there is no effective screening test for the disease and its symptoms are often vague, the majority of women are diagnosed at a late stage when survival rates are very low.

Early detection and accurate diagnosis are essential to increasing ovarian cancer survival rates. Researchers also believe molecular imaging holds promise for detecting ovarian cancer before it spreads into other areas of the body.

What is molecular imaging and how does it help people with ovarian cancer?

Molecular imaging is a type of medical imaging that provides detailed pictures of what is happening inside the body at the molecular and cellular level. Where other diagnostic imaging procedures—such as x-rays, computed tomography (CT) and ultrasound—predominantly offer anatomical pictures, molecular imaging allows physicians to see how the body is functioning and to measure its chemical and biological processes.

Molecular imaging offers unique insights into the human body that enable physicians to personalize patient care. In terms of diagnosis, molecular imaging is able to:

• provide information that is unavailable with other imaging technologies or that would require more invasive procedures such as biopsy or surgery
• identify disease in its earliest stages and determine the exact location of a tumor, often before symptoms occur or abnormalities can be detected with other diagnostic tests

As a tool for evaluating and managing the care of patients, molecular imaging studies help physicians:

• determine the extent or severity of the disease, including whether it has spread elsewhere in the body
• select the most effective therapy based on the unique biologic characteristics of the patient and the molecular properties of a tumor or other disease
• determine a patient’s response to specific drugs
• accurately assess the effectiveness of a treatment regimen
• adapt treatment plans quickly in response to changes in cellular activity
• assess disease progression
• identify recurrence of disease and help manage ongoing care

Molecular imaging procedures generally are noninvasive, safe and painless.

How does molecular imaging work?

When disease occurs, the biochemical activity of cells begins to change. For example, cancer cells multiply at a much faster rate and are more active than normal cells. Brain cells affected by dementia consume less energy than normal brain cells. Heart cells deprived of adequate blood flow begin to die.

As disease progresses, this abnormal cellular activity begins to affect body tissue and structures, causing anatomical changes that may be seen on CT or MRI scans. For example, cancer cells may form a mass or tumor. With the loss of brain cells, overall brain volume may decrease or affected parts of the brain may appear different in density than the normal areas. Similarly, the heart muscle cells that are affected stop contracting and the overall heart function deteriorates.

Molecular imaging excels at detecting the cellular changes that occur early in the course of disease, often well before structural changes can be seen on CT and MR images. Similarly molecular imaging can detect treatment-induced cellular activity changes earlier than structural changes.

Most molecular imaging procedures involve an imaging device and an imaging agent, or probe. A variety of imaging agents are used to visualize cellular activity, such as the chemical processes involved in metabolism, oxygen use or blood flow. In nuclear medicine, which is a branch of molecular imaging, the imaging agent is a radiotracer, a compound that includes a very small amount of radioactive atom, or isotope. Other molecular imaging modalities, such as optical imaging and molecular ultrasound, use a variety of different agents. Magnetic resonance (MR) spectroscopy is able to measure chemical levels in the body, without the use of an imaging agent.

Once the imaging agent is introduced into the body, it accumulates in a target organ or attaches to specific cells. The imaging device detects the imaging agent and creates pictures that show how the imaging agent it is distributed in the body; this distribution pattern helps physicians discern how well organs and tissues are functioning.

What molecular imaging technologies are used for ovarian cancer?

The molecular imaging technologies currently being used for ovarian cancer are positron emission tomography (PET) scanning and PET in conjunction with computer-aided tomography (CT) scanning (PET-CT).

What is PET?

PET involves the use of an imaging device (PET scanner) and a radiotracer that is injected into the patient’s bloodstream. A frequently used PET radiotracer is ¹⁸F-fluorodeoxyglucose (FDG), a compound derived from a simple sugar and a small amount of radioactive fluorine. It usually takes between 30 and 60 minutes for the FDG to distribute throughout the body.

Once the FDG radiotracer accumulates in the body’s tissues and organs, its natural decay includes emission of tiny particles called positrons that react with electrons in the body. This reaction, known as annihilation, produces energy in the form of a pair of photons. The patient is placed in a PET scanner, which detects these photons and creates three-dimensional images that show how the FDG is distributed in the area of the body being studied.

Because highly active cancer cells absorb more glucose than normal cells, they appear brighter on PET scans. So, areas where a large amount of FDG accumulates, called ‘hot spots’ because they appear more intense than surrounding tissue, indicate that a high level of chemical activity or metabolism is occurring there. Areas of low metabolic activity appear less intense and are sometimes referred to as ‘cold spots.’ Using these images and the information they provide, physicians are able to evaluate how well organs and tissues are working and to detect abnormalities.

PET-CT is a combination of PET and computed tomography (CT) that produces highly detailed views of the body. The combination of two imaging techniques—called co-registration, fusion imaging or hybrid imaging—allows information from two different types of scans to be viewed in a single set of images. CT imaging uses advanced x-ray equipment and in some cases a contrast-enhancing material to produce three dimensional images. A combined PET-CT study is able to provide detail on both the anatomy and function of organs and tissues. This is accomplished by superimposing the precise location of abnormal metabolic activity (from PET) against the detailed anatomic image (from CT).

Scans are reviewed and interpreted by a qualified imaging professional such as a nuclear medicine physician or radiologist who shares the results with the patient’s health care provider.

How is PET used for ovarian cancer?

Physicians use PET and PET-CT studies to:

• diagnose and stage: by determining the exact location of a tumor, the extent or stage of the disease and whether the cancer has spread in the body, especially the lymph nodes.
• plan treatment: by selecting the most effective therapy based on the unique molecular properties of the disease and of the patient’s genetic makeup and to determine a site that is appropriate for biopsy, if necessary
• evaluate the effectiveness of treatment: by determining the patient’s response to specific drugs and ongoing therapy. Based on changes in cellular activity observed on PET-CT images, treatment plans can be quickly altered
• manage ongoing care: by detecting the recurrence of cancer

What are the advantages of PET studies for ovarian cancer patients?

PET-CT is highly accurate at detecting recurrent ovarian cancer and more accurate than CT imaging alone.

• PET-CT is useful for:
  • staging the disease
  • determining whether the cancer has spread elsewhere in the body
• Information provided by PET-CT scans:
  • often results in a change in patient management
  • may determine the effectiveness of therapy after just one cycle of treatment
  • may eliminate unnecessary surgeries after treatment by differentiating between tumors and benign residual masses.

Are molecular imaging procedures covered by insurance?

PET-CT studies for many cancers, including ovarian cancer, are covered by Medicare and Medicaid. Major insurance companies and health maintenance organizations also provide coverage for PET-CT studies for cancer. Patients being treated for a cancer that is not currently covered by insurance may be eligible for reimbursement by participating in the National Oncologic PET Registry (NOPR).

Patients should check with their insurance companies for specific information on their health plan’s coverage and payment policies.

What is the future of molecular imaging and ovarian cancer?

There are many new and emerging molecular imaging technologies that may benefit people with ovarian cancer, including:

• hybrid imaging systems, such as combined PET-MR, which may improve accuracy and allow physicians to see how cancer is affecting other systems in the body
• the use of PET imaging other biomarkers, such as fluorothymidine (FLT) to show tumor proliferation
• molecular radiotherapy (MRT).

What is Molecular Radiotherapy (MRT)?

Molecular Radiotherapy(MRT) is a cancer treatment that uses targeted and localized radiation therapy to destroy cancer cells with a generally lower toxicity than traditional systemic chemotherapy. MRT is also known as radioimmunotheraphy (RIT).

In MRT, a radioactive agent is attached to a substance called a monoclonal antibody that is designed to recognize and bind to a specific cancer cell. When injected into the patient’s bloodstream, the agent/antibody travels and binds to the cancer cells, allowing a high dose of radiation to be delivered directly to the tumor.

Several new MRT agents are under development or in clinical trials.