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FDG-PET image reveals tumor

The Nuclear War Against Cancer

August 2002

by Natalie Gutierrez

Three Mile Island. The atomic bomb. Powerful images come to mind when we hear the word "nuclear." But forms of nuclear energy have been used in medical science to save people’s lives for nearly a century. Physicians in the radiation oncology department are integrating nuclear medicine technology in their fight against cancer. The department, with the benefit of high-tech equipment from the Cancer Therapy and Research Center (CTRC), is at the forefront of cancer treatment and research.

The Health Science Center is one of a select few institutions in the world to combine Fluorodeoxyglucose (FDG) Positron Emission Tomography (PET), or FDG-PET, imaging with Computed Tomography (CT) imaging using an exciting new computer technology called image fusion. Using special computer software, Martin Fuss, M.D., assistant professor in the department of radiation oncology, takes a patient’s PET scan and places it on top of the patient’s CT scan. The software allows him to align the images so they rest perfectly (anatomically correctly), one on top of the other. By closely examining the fused image, Dr. Fuss can better determine the extent of malignant tumors and then prescribe and deliver the most precise and individualized radiation therapy available - a process that until one year ago could not be done.

"In the past, when it was determined that a cancer patient required radiation therapy, doctors prescribed a standard treatment," Dr. Fuss said. "Today we can optimize radiation treatments and tailor them to the specific medical needs of each patient. Computed Tomography (CT) and/or Magnetic Resonance Imaging (MRI) scans allow us to determine more precisely the target area that needs to be irradiated."

(Right) A CT scan shows a cross section (top) and a frontal view (bottom) of the lung revealing the tumor as a white mass. The blue, red, yellow and green lines (isodose lines) surrounding the tumor indicate the area to be targeted with radiation treatment. (Left) The CT image is fused with the FDG-PET image and aligned perfectly. The blue, red, yellow and green isodose lines are taken from the CT scan and superimposed onto the fused image.

  CT image fused with FDG-PET image
Dr. Fuss said that although significant improvements have resulted from their use, CT and MRI images alone cannot always depict subtle differences between tumor and functional tissues. For example, a bundle of scar tissue could resemble a tumor or vice versa, and small lymph nodes that appear normal can actually harbor tumor cells.

"These factors could result in an inaccurate interpretation of the extent of the disease," Dr. Fuss said. These misinterpretations may subject patients to the risk and expense of unnecessary medical procedures, such as repeated tissue sampling, surgery, chemotherapy or large-field radiation. The fusion of FDG-PET with CT and MRI images has significantly decreased those risks.

Christine Waters, 78, a breast cancer survivor, was one of the first patients to benefit from the FDG-PET and CT image fusion technique. Six years after she had a complete mastectomy, Waters was diagnosed with lung cancer. Doctors determined she was not strong enough to undergo additional surgery, so radiation therapy was the treatment of choice. Waters’ doctors sent her to the CTRC to undergo a CT and FDG-PET scan.

Health Science Center radiation oncologists injected FDG, a completely safe, mildly radioactive substance, also called a radiopharmaceutical, into her vein. Mistaking the radioactive glucose molecule for food, the cancer cells in her lung quickly absorbed the FDG. A large PET scanner then took pictures of her upper body. The images measured the radiation emitted by the FDG and revealed the tumor as a discrete glowing mass of color in her chest.

"The more of the radiopharmaceutical the cancer absorbs, the brighter the color in the image," Dr. Fuss said. "Christine’s PET image indicated that her cancer was at Stage 1, meaning it was a small tumor that had not yet metastasized into her lymph nodes. The PET study allowed us to catch her tumor at a very early curable stage."

Instead of having to endure 37 days of radiation therapy and four chemotherapy treatments, Waters underwent three days of precisely targeted, or stereotactic, radiation therapy in combination with chemotherapy.

"I was thrilled when I found out I wouldn’t have to undergo a lengthy course of radiation and chemotherapy treatments," Waters said. "I was worried about the side effects such a long treatment schedule would have on someone my age. The fact that the doctors were able to catch my cancer early and get me the individualized treatment I needed was wonderful."

This month, Waters will return to the CTRC for a follow-up FDG-PET scan. Dr. Fuss will use image fusion technology to evaluate the effectiveness of the radiation therapy.

Although FDG-PET imaging is still relatively expensive, about $1,200 per scan, Dr. Fuss said that as the procedure becomes more widely used, more insurance plans will begin to cover its cost.

In addition to treating patients, Health Science Center faculty continue to provide top-notch training to young physicians. Last year, the Health Science Center began offering its newest doctoral program - the combined medical residency Ph.D. in Human Imaging within the Radiological Sciences program. Sean Cavanaugh, M.D., the first Texas resident selected for the American Board of Radiology’s (ABR) B. Leonard Holman Research Pathway, will be the first graduate of this new program. The acceptance of Dr. Cavanaugh into this highly competitive research pathway reflects the professional excellence of Health Science Center faculty and the availability of outstanding imaging resources to the university.

The five-year program combines training in research with training in radiation oncology or radiology. The program is unique in that the young physician must work closely with the residency director and his research mentor to design an appropriate training plan that incorporates serious research without jeopardizing the clinical training required for ABR board certification.

Together with his mentor, Dr. Fuss, Dr. Cavanaugh is developing new PET imaging techniques to detect and stage prostate and brain cancer. They believe the techniques used for Waters’ radiation treatment will eventually benefit larger numbers of cancer patients.

Waters said she feels lucky to live in San Antonio where this new approach is available.

"Cancer runs in my family," she said. "My mother died of breast cancer when she was 72. I feel much more at ease knowing that the technology is here today to help those of us at risk. I wish my mother could have benefited from what doctors know today. I know my daughter, Christye, and I will benefit."



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Updated 12/11/14