Oncology imaging is booming. Many new imaging technologies such as PET and virtual colonoscopy have been successfully launched and are taking hold. And new applications are being adopted for older technologies. Take MRI, for example, which is being applied for both screening and diagnostic purposes in breast cancer. The decades-long debate over lung cancer screening could be settled in the not-too-distant future when the National Lung Screening Trial (NLST) draws to a close. Finally, ultrasound and CT are guiding new interventions such as cryosurgery and radiofrequency ablation (RFA).
The downright breakneck speed of advances is occurring as baby boomers age and require additional imaging tests to diagnose and manage cancer. Kalorama Information (New York City) predicts that the number of imaging procedures worldwide for cancer diagnosis and patient management will increase from 115 million scans in 2001 to 158 million procedures in 2006. This figure excludes virtual colonoscopy and breast cancer devices. Both areas could see significant gains in the next few years. In fact, Joel Rubenstein, MD, PhD, diagnostic radiologist with Epic Imaging (Portland, Ore), says, “Virtual colonoscopy will be the biggest-growth cancer imaging test that we do.”
Virtual Colonoscopy Goes Mainstream
Virtual colonoscopy follows some general trends in cancer detection. That is, noninvasive tests that cost less and are less damaging to the patient are being increasingly used. Rubenstein explains, “Virtual colonoscopy is an alternative to regular colonoscopy for the average-risk patient and for those who refuse conventional colonoscopy. It allows us to do a noninvasive test for a pretty low-frequency cancer.”
The colon is ideal for this type of screening because colon cancers are typically slow-growing and start as polyps. At Epic Imaging, a 1-cm polyp detected by virtual colonoscopy is considered significant and referred for follow-up. Colonoscopists, on the other hand, may biopsy polyps as small as 2–3 mm because they are already in the colon. Although fewer polyps may be biopsied with virtual colonoscopy, the procedure could result in an increased cancer yield because average- risk patients accept the test more readily than conventional colonoscopy. At the same time, unnecessary (and expensive) biopsies may be avoided.
Rubenstein continues, “Virtual colonoscopy has seen a fairly rapid evolution, and it is improving. The ideal will be a prepless test.”How would it work? The patient would drink a contrast that labels stool, and the computer would remove the stool from the image and label the polyps. Rubenstein says the prepless test may be available in the next few years. While virtual colonoscopy has seen fairly rapid adoption as a screening tool, other new technologies have been implemented for staging purposes. Take PET, for example, which is increasingly used in oncology.
The PET Evolution
In just a few short years PET has made the shift from a university research center modality to a mainstream modality. It is, along with CT, the primary imaging modality for cancer staging. One reason behind its adoption is reimbursement. And PET has been reimbursed and implemented because the scans work beautifully for oncology imaging. Patricia S. Gordon, MD, director of radiation oncology at Century City Hospital (West Los Angeles, Calif), explains, “PET gives us the ability to feel relatively safe that the cancer has not spread beyond where we think it is. It also allows us to monitor the course of chemotherapy.”
PET has been used in lymphoma and melanoma and in lung, colorectal, cervical, head and neck, and esophageal cancers. It is increasingly used in Stage 2 breast cancer cases. PET adds to the breast cancer imaging arsenal because it makes it easier to locate the lymph nodes and bony metastases than other scans do. Another relatively new option is PET-CT, which is increasingly utilized for lung cancer staging. The advantage of PET-CT is the ability to register the anatomy and localize the tumor.
Despite a fairly healthy list of advantages and applications, there are a few downsides to PET. Rubenstein explains, “PET and PET-CT have been overused in the wrong situations.” For example, a few years ago some radiologists were doing breast PET scans before the evidence demonstrated the clinical utility of the scan. Sometimes, a PET scan is ordered for very small lung lesions when the size of the lesion does not meet the threshold for PET. Still, Rubenstein concludes, “These issues are a matter of use and not about PET itself.”
The Advent of Breast MRI
Like PET and virtual colonoscopy, breast MRI appears to be finding its niche. Since 1999, there has been a 40% boost in breast MRI examinations in the United States, particularly in staging cancer, monitoring the response to breast therapy, and screening high-risk patients. In May, the American Cancer Society endorsed breast MRI’s position with an update of guidelines for breast cancer screening that said that breast MRI, when used with mammography, may enhance the effectiveness of screening and diagnosis. Approximately 8.5 million American women are described as at high risk for breast cancer. “We’re seeing more and more patients come in with breast MRI scans,” Gordon notes. “As radiologists get more comfortable reading them, we’re going to be able to find more cancers that we have not found on mammograms.”
Nancy Elliot, MD, FACS, director of Montclair Breast Center (Montclair, NJ), agrees and is so convinced of the modality’s utility in breast cancer that she has decided to implement screening MRI in her practice. She explains, “One area where breast MRI use is not controversial is in women already diagnosed with breast cancer. We can use MRI to make sure that the woman is a good candidate for lumpectomy and to rule out cancer in the opposite breast.” Elliot, however, intends to go one step farther, and her rationale makes a lot of sense. Currently, the Centers for Medicare and Medicaid Services (CMS of Washington, DC) have approved breast MRI for women with the BRCA 1 or BRCA 2 gene. Elliot notes, “It’s not a far jump from women with a 30% risk of breast cancer [ie, women with the gene] to women with a 28% risk [ie, other high-risk women]. Breast MRI is ideal for us because we see a lot of high-risk women who have a family history of the disease, atypical changes in the breast, and had previous breast cancer.”
MRI can be an effective breast cancer–screening tool because it is a dynamic and structural test. It analyzes function via the injection of gadolinium, and it provides architectural views of the breast. While mammography provides a mere four images, MRI provides thousands of 3-mm slices. As a result, the average size of breast cancer detected by MRI is 5 mm compared with 12 to 15 mm on a mammogram. “This early pickup can be a cost-savings in the end because at 5 mm the woman will not require chemotherapy,” explains Elliot.
The Search for Answers About Lung Cancer Screening
Cancer screening is a tricky business. Breast MRI may or may not be accepted. And it is not the only type of cancer undergoing screening scrutiny. Although there are currently no modalities approved for lung cancer screening, some groups tout spiral CT as a screening solution. Others believe chest x-rays do the job. Still others claim that early screening will not translate into saved lives.
The American College of Radiology Imaging Network (ACRIN) and the Prostate, Lung, Colorectal, and Ovarian (PLCO) cancer screening trial are undertaking a joint 8-year study. The NLST will determine, which, if either, screening modality is more effective at reducing lung cancer deaths. But final data will not be available for years.
Denise Aberle, MD, professor of radiology at the University of California, Los Angeles, and a principal investigator in the NLST, explains, “Right now, our understanding of lung cancer screening using either modality is incomplete.” A few early observations can shed a bit of light on the situation. For example, Aberle says, “We know without a doubt that chest CT is more sensitive [than chest x-ray]. It picks up more nodules and cancers and more early-stage cancers. It does not pick up fewer late- stage cancers.” Because late-stage lung cancer is uniformly lethal, if there is not a decrease in late-stage cancer, researchers do not expect a decrease in mortality. Aberle says, “This suggests that screening CT picks up more indolent cancers that patients would die with but not from.” It is important to note, however, that the jury is still out and researchers could detect a true stage shift toward earlier diagnosis with screening CT as more data become available. Another wrench in the screening CT scenario is that tumor size does not necessarily correlate with biology. That is, a small lesion detected by screening CT could be a late-stage lesion, so the intuitive benefit associated with detecting smaller lesions may not occur. Aberle concludes, “At this point, the data do not show any benefit from screening CT, but it could be hidden from the small size of earlier trials.” The final answers will be available as the NLST draws to a close in 2009.
Interventional Radiology and Oncology
Prostate cancer treatment is notoriously problematic. Gary Onik, MD, director of The Center for Surgical Advancement at Florida Hospital Celebration Health (Celebration, Fla), explains, “Treatment often leaves men impotent or incompetent. Until this point, treating prostate cancer was based on an all-or-nothing rationale. Surgical treatment is not amenable to taking a portion of the prostate gland. Brachytherapy is really confined to very low-risk patients.”
Male Lumpectomy Upper left: An MRI of the prostate with a small area of decreased signal in the left peripheral zone. Upper right: A prostate ultrasound with an area of decreased echogenicity that corresponds to the MRI abnormalility. Lower left: A cryoprobe in the same lesion. Lower right: The freezing of the area as a hyperechoic rim with posterior acoustic shadowing. This patient was fully continent and sexually active one week after the procedure.
Eight years ago, Onik began researching cryosurgery as a treatment for prostate cancer. The treatment employs ultrasound imaging for tumor localization; cryosurgery destroys tumors by freezing them. The technique has been dubbed the male lumpectomy because the situation for men with prostate cancer is similar to that for women with breast cancer.
The first step in Onik’s research was determining if prostate patients could be treated focally. The answer, for most patients, is yes. Onik reports, “The literature shows a large percentage of patients are amenable to focal treatment. Thirty percent to 35% of men have only one focal tumor. The 45% of the remaining patients have microscopic tumors of less than 5 mm. So, overall 75% to 80% of men can be treated focally.” The next step was to determine if whole-gland cryoablation is safe and efficacious. Onik says long-term 5- and 7-year data show that cryoablation is competitive with surgery and radiation treatment. Moreover, it appears that cryoablation can control cancer and limit complications such as impotence and incontinence. Another plus in the cryoablation file is that cryoablation can be repeated as needed unlike with surgery or radiation therapy. In addition to these patient care benefits, cryosurgery is also associated with lower costs. It is an outpatient procedure, and most patients don’t require hormone treatment or radiation.
Still cryoablation is in its infancy. Onik predicts better imaging procedures will make it possible to treat some patients with bilateral disease. MRI prostate spectroscopy combined with a saturation biopsy completed every 5 mm can provide more accurate and detailed information on the location of the disease, which could make some bilateral patients eligible candidates for cryosurgery. Although Onik waxes positive, he is realistic. “Nothing matters until the results are reproduced.” A multi-institutional prospective study to reproduce the results is under way. Onik concludes, “If our results are reproduced, this will be the way that prostate cancer is treated. I guarantee it."
Prostate cancer patients are not the only ones benefiting from radioablative techniques. Radiofrequency ablation is being increasingly used in liver cancer.
How does it work? Under ultrasound or CT-guidance, an interventional radiologist inserts a needle into a tumor and destroys it with mild radiofrequency energy. The hitch? Radiologists can cook only a small area at a time. Larger tumors require multiple overlapping burns, which are difficult to control. RFA does not cure liver cancer, but it can shrink or control the tumor. Michael Soulen, MD, associate professor of radiology and surgery at the University of Pennsylvania (Philadelphia), reports, “With a 2- to 3-cm tumor, 80% of patients have no recurrence [at the RFA site] in 1 year after RFA.” That figure drops to 50% as tumors increase in size to 4 cm, and most patients will fail if the tumor is 5 cm. RFA can be repeated as new spots appear in other places on the liver, which is typically the case with liver cancer.
Soulen explains, “One reason behind the increasing use of RFA is that more patients are being screened and we’re finding smaller tumors. Another reason is patients with metastatic disease are being referred.” The rationale is that RFA can keep the tumor from growing and prevent patients from dying of liver failure; this, however, has not been studied in a randomized trial. RFA is also being applied in lung and kidney cancer in patients who are not candidates for surgical resection. Finally, RFA can be used to control pain caused by bony metastases if a specific metastasis is causing the pain.
Although the recent upsurge in RFA is not the result of technological advances but rather a function of the demographics of liver cancer and increased awareness among oncologists, researchers are working on improvements. One promising area is combining thermoablation with catheter-directed therapy to cut off blood flow to the liver. Soulen explains, “This allows radiologists to get a bigger and better burn and may allow us to treat 6- to 9-cm lesions.” Another technology in the works could allow radiologists to power multiple probes at once, resulting in a more predictable placement of probes. Finally, improvement in imaging technology could simplify RFA. Ultrasound may be the modality of choice simply because it is easy to work around. It is also the least conspicuous modality for liver tumor visualization. CT allows interventional radiologists to see better, but it is more awkward. The scanner limits probe placement. Soulen continues, “With both modalities, you can’t tell if you cooked the tumor or not during the procedure. MRI is great because it’s the best modality for seeing liver tumors and you can actually do temperature-sensitive scanning. The problem is how to do RFA inside a magnet.” Vendors have taken notice of these issues, and a few companies are working on modifying MRI scanners to be compatible with RFA.
Oncology imaging advances are coming at a fast and furious clip. Some techniques will enable better screening, while other potential screening options may be abandoned because they fail to translate into decreased mortality. Other imaging techniques will allow physicians to better identify the extent of the disease and therefore better tailor treatment for patients diagnosed with cancer. Finally, increased use of radioablative techniques could spell improved outcomes for men diagnosed with prostate cancer and possibly better local control of tumors in the liver, lungs, or kidneys.
