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October 8 , 2007

Changing Cancer Care — Imaging’s Role Advancing Diagnosis and Treatment
By Beth W. Orenstein
Radiology Today
Vol. 8 No. 20 P. 12

Technological advances in scanners and software are revolutionizing the diagnosis and treatment of cancer.

For many years, imaging—plain film x-ray, MRI, CT, and ultrasound—has provided anatomical information, says Reginald Munden, DMD, MD, section chief and professor of thoracic imaging in diagnostic radiology at the University of Texas M. D. Anderson Cancer Center in Houston.

During the last decade or so, imaging equipment manufacturers have been able to combine scanning techniques with improvements in software to provide functional information as well. According to Munden, as well as colleagues at other major cancer centers, being able to combine anatomical and functional imaging has ushered in a new era for cancer diagnosis and treatment.

The new techniques allow physicians to see more clearly inside the body, allowing them to diagnose cancers earlier—often when they are more treatable. New combination modalities and techniques are allowing physicians to not only find but also treat cancer with extraordinary precision and monitor the efficacy of a given treatment more quickly and with more accuracy.

One key has been the development of scanners that combine PET, which provides metabolic function at the cellular level, with the anatomical context of CT scans.

Early Warning
PET will reveal metabolic changes at the cellular level, which is one of the first indications of malignancy. Such changes are often evident long before structural abnormalities develop, says Michael Yu, MD, chief of nuclear medicine and PET services at Fox Chase Cancer Center in Philadelphia.

In the past, physicians would order a CT scan, which would be done on one machine, to see anatomic detail and a PET scan, which would be done on another scanner, to look for metabolic changes. The problem was being certain that the PET and CT scans were imaging the exact same area and position.

In the late 1990s, manufacturers began working on a combination PET/CT scanner. The first commercial PET/CT scanner was introduced in late 2001. It revolutionized the field, Yu says. A PET/CT scan performed at the same time on a single machine provides fused images that allow physicians to place information about cellular activity in accurate anatomical context.

With PET/CT, Yu says, physicians no longer have to make assumptions about the location of a malignancy. They know with improved certainty, and possibly quite early on, where it is. “The information helps with accurate staging and restaging of the patients, surveillance for residual or recurrent disease, and monitoring treatment,” Yu says.

Also, if the PET/CT scan indicates cancer, it allows the physicians to define a more targeted treatment plan for better radiation therapy, according to Yu. Better planning enables physicians to deliver stronger doses to the tumor, while not harming surrounding healthy tissue and decreasing the treatment side effects, he says.

Today, PET/CT is used for many cancers, especially lymphoma, lung, esophageal, colorectal, and head and neck cancers, Munden says. It is also increasingly applied to other cancers, including melanoma, breast, sarcoma, and cervical cancers. Yu notes that PET/CT has shown particular advantages for head and neck cancers where there are a lot of small structures requiring evaluation.

PET Registry
In an unusual step for the Centers for Medicare & Medicaid Services, Munden says, it has been offering broad coverage for PET/CT to include the diagnosis, staging, restaging, and therapy monitoring of nearly all malignancies. The coverage is dependent on the referring physician participating in the National Oncology PET Registry (NOPR), which is sponsored by the Academy of Molecular Imaging and endorsed by the American College of Radiology (ACR), the American Society of Clinical Oncology, and the Society of Nuclear Medicine. The NOPR is managed by the ACR and the American College of Radiology Imaging Network.

“PET/CT is not the end-all of answers” because some tumors do not take up the most commonly used tracer, fluorodeoxyglucose, according to Munden. Also, some infections can take up the tracer and mimic cancer. “However,” he says, “when all is said and done, it is the best thing we have right now to look at a larger number of tumors and determine if this particular lesion is characteristic of what we see in other cancers.”

Also, new radioactive tracers are in development, and researchers are optimistic that they will continue to provide more information about how fast a tumor is growing, how much oxygen it is using, how much blood supply it has, and its resistance to drugs.

Multislice CT scanners are also helping to improve cancer treatment and diagnosis. Four-slice CT scanners were introduced in 1998. Since then, “We’ve gone to multislice CT scanners, and the advantage of those is that they can image rapidly, and you don’t have the motion degradations that were a problem in the past,” says Rosaleen B. Parsons, MD, chair of the department of diagnostic imaging at Fox Chase.

The faster the scanner, the less the motion, Parsons explains. “So you can exclude an abnormality that might not be a lesion because you have gotten rid of the motion. We used to have a lot of problems in the past, especially in the liver, where you weren’t sure whether you were looking at a liver lesion or just the top of the bowel. With a multislice CT scanner, you’ve eliminated that issue,” she says.

Physicians also are able to use multislice scanners to assess blood flow. Tumors tend to grow abnormal blood vessels, and treatments are often aimed at reducing blood flow. “So if you take a baseline, then give the patients chemotherapy, and then reassess the perfusion after they’ve been given the chemotherapy, if there has been a reduction to the blood flow, you know that the therapy is working,” Parsons says. “If there’s no reduction, you might adjust the treatment.”

Perfusion Assessment
How soon after treatment a follow-up perfusion CT scan can be done depends on the protocols and tumor type. Most patients are imaged six to eight weeks later with CT, Parsons says, but the results are not always black and white. “Sometimes, you find one lesion has gotten smaller while another has gotten bigger. Sometimes, you get a mixed response, and then you have to decide whether to change the course,” she says.

Multislice CT scans also help eliminate surgical biopsies in some patients, Parsons says. “In the past, a patient may have had to go to the operating room. But with imaging, CT, and ultrasound, we can see the lesion pretty clearly and percutaneously sample the abnormality,” she says. The pathologists can then determine whether it is malignant. “That’s particularly important in patients with multiple different types of tumors—perhaps a breast cancer and a colon cancer—and a new liver abnormality,” she says. “With image guidance, the lesion can be sampled and the tissue type determined, which will then guide treatment.”

Improvements in the software used to interpret the images are also having an impact on how physicians measure tumor shrinkage, which is key to knowing whether a chosen course of treatment is working. Munden explains that most oncologists now use the guidelines known as Response Evaluation Criteria in Solid Tumors Group (RECIST) to measure a tumor’s response to treatment. RECIST criteria are based on a 2-D measurement.

With current image analysis software, it is possible to render the lesion in three dimensions, which allows a true volumetric analysis. “Volumetric analysis will take every little piece of tumor and measure it to give you a total volume. The science for anatomic analysis of tumors is heading that way,” Munden says. The sophistication will provide a greater ability to accurately assess treatments and determine whether they should continue or be altered.

Advances with other modalities, such as MR, also are impacting cancer treatment and diagnosis. Oncologists are not only looking at perfusion with MR but also oxygenation of tissues, which is another indication of whether a particular therapy is effective, Parsons says. “If we are able to get an oxygenation measurement before treatment and compare it to an after, we can see whether there has been cell death and know whether the chosen chemotherapy is working,” she explains.

MR Spectroscopy
Some researchers also use MR spectroscopy to measure biochemical changes in tumors. MR spectroscopy is beginning to play a role in distinguishing a recurrent tumor from tumor-related changes, Parsons says. Again, the earlier a tumor or recurrent tumor is identified, the earlier treatment can be implemented. Also, if changes are identified as benign, it can prevent unnecessary therapy, she says.

Spectroscopy has been well-established for examining brain tumors and is now being used more often for prostate cancer, Parsons says. MRI is also being used for earlier detection of breast cancer in women with dense breasts.

Imaging is not only helping to identify cancers earlier and better target therapies, but it is also playing an increasingly important role in delivering treatment to cancers.

Interventional Role
Image-guided treatments, namely chemoembolization and radiofrequency ablation (RFA), are playing a large role in the treatment of liver cancer, Parsons says. Performed by interventional radiologists skilled in the vascular system, chemoembolization is used to deliver targeted treatments via catheter throughout the body. Parsons notes that chemoembolization is a palliative, not a curative, treatment. However, she says, it can be extremely effective in treating primary liver cancers, especially when combined with other therapies. It also has shown promising early results with some types of metastatic tumors.

The individual materials used in chemoembolization are FDA-approved; however, the treatment itself is not approved for the intra-arterial therapy of liver tumors.

With RFA, the interventional radiologist guides a small needle through the skin into the tumor. Radiofrequency energy similar to microwaves is transmitted to the tip of the needle, where it produces heat in the tissues. The heated tissues die, and dead tumor tissue shrinks and slowly forms a scar. The FDA has approved RFA for the treatment of liver tumors.

Thanks to the many advances that imaging is offering cancer patients, it is also changing the radiologist’s role, Parsons says. “It used to be [that] the radiologist was in the dark room and people came by to see him or her for a consultation. Now, radiologists are part of the team,” she says.

Because imaging is changing cancer diagnostics and treatment, it is becoming more important that the radiologist be part of the patient’s care team, Parsons says. “The radiologist today definitely assists in patient care and management and can suggest alternative imaging that might clarify things and be better for the patient.”

— Beth W. Orenstein is a freelance writer and a regular contributor to Radiology Today. She writes from her home in Northampton, Pa.