Combining Technologies

Sixteen women with metastatic ovarian cancer, who participated in a University of Pittsburgh School of Medicine (UPSM) study, have become part of a growing number of cancer survivors.

The study scanned the women using a new fusion technology that combines PET, which images cells and cellular functions, and CT, which provides images of tissues, organs, and bones. This hybrid PET-CT scanner found metastatic lesions that other scans (CT alone or ultrasound) had missed, allowing oncologists and surgeons to intervene with treatment plans before the women's cancers were beyond treatment.

"The research has changed these patients' cancer management plans," says Dr. Todd Blodgett, a radiologist at UPSM. "PET-CT can define the tumor volume and location so radiation therapy can be delivered more accurately with localized boosts of radiation, targeting the tumor and shrinking it. By identifying the lesions earlier and targeting them more quickly, we hope to change the outcome."

In fact, the research, soon to be published, shows that PET-CT is identifying 75 to 80% more gynecological metastatic cancers than other diagnostic imaging exams, Blodgett says.

A Brief, But Impressive, History

The PET-CT was developed jointly by David Townsend, PhD, currently senior PET physicist and professor of radiology at UPSM, and Ronald Nutt, PhD, president of CTI Molecular Imaging in Knoxville.

While studying in Switzerland, the pair realized the value of simultaneously performing the two types of exams. Each procedure would enhance the other. "The body is kind of a flimsy structure," Nutt said in a TIME magazine interview. "If you lay it on the bed one time for a CT scan and another time for a PET scan, just a small difference in body position will result in the organs shifting about, so it's very difficult to do all that matching."

In 1995, Nutt and Townsend received a US$1.5 million (C$2.4 million) grant from the US National Cancer Institute and built a prototype scanner at the University of Pittsburgh. After researchers completed 350 scans on it, the US Food and Drug Administration approved the prototype in 2000. That same year, the newly introduced PET-CT scanner was designated by TIME magazine as the "Discovery of the Year."

Ken Manning, marketing director for CTI, says new generations of the scanner have been able to whittle minutes off the length of the exam, cutting time from 30 to 15 minutes. An added bonus is that these scanners are versatile and may be used to perform PET and CT, only PET, or only CT.

A goal for future scanners is to administer radiation therapy immediately after the scans, while the patient is still in position, thus ensuring that the radiation targets the tumor in its precise location and alignment.

PET-CT scanners are sold through CTI, Siemens Medical Solutions, Philips Nuclear Medicine, and GE Medical Systems. One hundred and fifty of these multimillion-dollar dedicated PET-CT scanners will be operating throughout the world by the end of 2002.

The majority of these scanners are found in the US. The first and only PET-CT scanner in operation in Canada was acquired in 2002 by St. Joseph's Health Care and the Lawson Health Research Institute in London, Ontario. Initially, they plan to use their new GE Discovery LS machine for research trials involving not only oncology patients, but also cardiac and neurology patients.

Issues and Goals

In the US, a major issue is cost: public and private insurance reimbursements for the exams amount to several thousand dollars. Currently, the US Centers for Medicare and Medicaid Services cover the PET-CT scans only for cancers of the head and neck, esophagus, breast, and lung, as well as lymphoma, colorectal, and melanoma – not for gynecological metastatic cancers.

As a result of the funding situation, a short-term goal for Blodgett and his UPSM colleagues is to gain reimbursement for the PET-CT scans for gynecological cancers. "These cancers are notoriously difficult to pinpoint in the body because they are in relatively small areas packed with many different types of tissues," he says.

PET-CT at Work

One of the PET-CT scanners, a blue, Volkswagen Beetle- sized GE Discovery was installed during summer 2002 at the clinic operated by X-Ray Associates of New Mexico in Albuquerque. Sagit Frasier, a nuclear medicine technologist and associate director of the imaging clinic, says it was the first such scanner in the Rocky Mountain region. The clinic uses PET-CT as a tandem procedure in the mornings and processes individual CTs on the Discovery in the afternoon.

"We can do a CT scan, eyes-to-thighs, in 27 seconds. The PET has six bed stops and takes about 30 minutes," Frasier explains from the dimly lit PET-CT room.

The patient enters the scanner on a sliding, motorized gantry. The imaging tunnel itself has two chrome rings about three feet apart. The first is the CT that beams a sheaf of X-rays through the body, generating a series of horizontal image slices, like a loaf of bread. The second is the PET crystal detectors.

For the CT exam, the radiologic technologist injects or provides the patient with a drink of contrast medium, usually iodine-based, that makes bones and organs stand out clearly.

For the PET exam, a technologist injects the patient with a sugar solution, which has molecules tagged with a radionuclide, usually fluorine 18. (Since the clinic does not have a cyclotron to produce this radionuclide, it is flown in from a facility in Texas on days they have a PET scan scheduled.) Tumors have a higher metabolism than surrounding tissues and use more of the glucose solution. Because of this faster uptake and a greater concentration in tumors and lesions, the radionuclide burns brighter at the tumor site, like a starburst, generating a "hot spot" in the dark, surrounding mass of the body on the PET image.

PET appears as a hot spot in space, but you can't pinpoint its location. To illustrate, Frasier points to a starry dot on a PET scan in the radiology reading room. It appears to be somewhere in the abdomen. With a click of her mouse, the computer blends the CT and PET scans, showing a hot spot in a nodule right outside the liver. "With this scan, our radiologists can direct the referring physicians to a precise location for further evaluation with a biopsy," Frasier says.

Or perhaps a nodule appears on a CT scan, but if the nodule is "cold" or doesn't appear on the PET scan "you can resolve it right then."

This new fusion technology makes possible the early diagnosis of metastatic cancers. The technology can also be expanded into other areas, such as cardiology where, for example, it could enable a doctor to examine the extent of damage to heart tissues following a heart attack. With the marriage of PET CT, the chances for improved treatment and increased patient survival rates are clear.

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