PET/CT Spreads Its Wings to Monitor Cancer Therapy
These PET/CT images of a patient’s chest with esophageal cancer, taken on the Philips Medical Systems Time of Flight system, demonstrate areas of increased uptake along the esophagus.

PET/CT is flexing its muscle in oncology imaging. Evidence of the hybrid scanner’s power is evident to anyone in the market for a standalone PET system—major vendors no longer market dedicated PET scanners. Combining CT’s anatomic imaging capabilities with PET’s metabolic detection provides a formidable resource for detecting, staging and restaging cancer as well as following up to manage patients effectively.

Hybrid PET/CT systems are making strides on several fronts. For starters, some sites are improving and accelerating patient care and trimming costs with sequential imaging. Others are taking advantage of the National Oncology PET Registry; the registry broadens oncology applications beyond those initially approved by the Centers for Medicare & Medicaid Services (CMS) and reimburses registered sites for such exams.

While PET/CT is a known powerhorse for diagnosing, staging and restaging cancer, the systems also show promise for monitoring a tumor’s response to therapy, which could lead to better patient care as its provides physicians with data needed to refine treatment based on each patient’s particular response to treatment.

Despite the clinical advances, IT continues to vex PET/CT. Image management is not quite geared to the specific needs of the hybrid modality. Upcoming PACS could better handle PET/CT images. Training is another can of worms as both interpreting physicians and technologists require a solid grounding in CT and PET. Finally, the three-to-five-year outlook remains very bright as researchers explore new radiotracers and radio-labeled antibodies.

The carefully honed enterprise

Diagnostic PET/CT Center of Chattanooga in Chattanooga, Tenn., is a sequential imaging PET/CT pioneer. Senior Staff Radiologist Joe Busch, MD, has used sequential imaging since 2004. The technique is simple and yields significant gains in efficiency and patient care. Instead of performing an attenuation CT scan followed by a PET scan, sequential imaging acquires a diagnostic CT followed by a PET study in one shot. It optimizes the CT component by using the CT to its potential rather than limiting its role to attenuation correction. The approach is more cost-effective and efficient than fusing separately acquired scans, says Busch, as it requires only a single room and one tech. Plus, the sequential technique produces more data and is easier on patients. “The patient undergoes one visit, one venipuncture and one radiation exposure. The scan is complete in 15 minutes,” says Busch, who uses Siemens Medical Solutions biograph 6 and biograph 16 PET/CT systems to complete about eight PET/CT scans daily. The approach benefits radiologists and nuclear medicine physicians as well as the interpreter who reviews both scans simultaneously—a workflow improvement over fusing separate images. What’s more, PET/CT can accelerate patient care. For example, a newly diagnosed colorectal cancer patient can be completely staged within one day of a PET/CT study with the exception of rectal staging via transrectal ultrasound.

PET/CT is a clinical boon in other cases as well. “It can be extremely helpful in staging lymph node pathology, enhancing pleural plaques and carcinomas of the head and neck or breast,” Busch says. In fact, local oncologists refer all head and neck cases to Diagnostic PET/CT Center of Chattanooga because they realize the capabilities of its equipment. “We use Siemens’ high-resolution techniques and IV contrast media to discern positive lymph nodes smaller than eight millimeters, which is critical in head and neck cancers,” explains Busch.

The integrated approach

Tacoma Radiology Associates in Tacoma, Wash., is a relative newcomer to the PET/CT arena. For the last several years, the practice focused on hybrid fusion via software to produce integrated imaging reports that incorporated not only PET and CT, but also MR and lab results. “We wanted to wait for a true advance in PET design before investing in PET/CT,” says Anthony Larhs, MD, director of nuclear medicine and clinical PET. Late last year, the practice invested in Philips Medical Systems Time of Flight PET/CT scanner. The hybrid system improves localization of information of interest, particularly as the patient’s girth increases; Time of Flight compensates for increased girth to produce images of consistent quality. The scanner also completes PET scanning at a rate of one image per bed position regardless of patient size, allowing the practice to schedule at least twice as many patients daily on the PET/CT scanner as it did on its PET system. Techs are able to complete most patient studies within 10 minutes, says Larhs.

The move to hybrid scanning has delivered other benefits as well. For example, Tacoma Radiology Associates used to employ a staff person to track CT images for hybrid fusion. The position is no longer necessary. “PET/CT allows us to condense services. We have one machine that combines anatomy and function in one place,” confirms Larhs.

Tacoma Radiology Associates is employing cutting-edge protocols that forego the traditional PET scan combined with a non-diagnostic transmission CT. The practice acquires diagnostic PET and diagnostic CT images on its PET/CT scanner to provide physicians with the information for a comprehensive report that describes the size, contour, density, location and metabolic activity of each lesion, which Larhs dubs “PETCT.” “It’s an education process,” admits Larhs. “We recommend and insist on diagnostic quality CT with each and every PET/CT exam.” The approach has no impact on exam time or workflow, says Larhs, but it adds considerable diagnostic value to the exam. The difference between a transmission CT and a diagnostic CT is fewer than 10 seconds. The hitch is tech training; a diagnostic CT requires a tech trained in CT, which means the tech should be dually trained in PET and CT.   

Looking into the future at the mega-enterprise

Memorial Sloan-Kettering Cancer Center in New York City, is a PET/CT pioneer; the premier cancer center phased out stand-alone PET by 2002, replacing its cameras with hybrid systems like GE Healthcare Discovery STE PET/CT scanners. The center plans to increase its current inventory of five PET/CT systems by another three in the next year, placing two of the new systems in a breast center and a center for image-guided intervention. It’s no surprise that Nuclear Medicine Chief Steve Larson, MD, foresees a dramatic increase in volume by 2010 from its current volume of 35 to 40 patients daily.

PET/CT is expanding beyond the initially approved applications, says Larson, mainly because the PET Registry opens the door to other types of cancers. Consequently, Memorial Sloan-Ketter-ing now deploys PET/CT for cancers that aren’t on CMS’ original approved list, such as prostate and neuro-endocrine tumors. “I think the data will show that PET/CT is useful as long as we carefully select patients for PET/CT studies,” says Larson. That is, the patient should present with a reasonable likelihood of disease. At the same time, the hybrid machines continue to play a critical clinical role in staging disease and detecting recurrent tumors and metastases.

Despite the promise, there are still some bugs to work out of PET/CT. On one end, vendors are producing new scanners with improved detectors for better image quality. On the other, image management still hinders hybrid scanning. The biggest beef? Physicians can’t compare serial PET/CT studies at PACS workstations. The standard approach is the dedicated PET/CT workstation, a known workflow-buster, but Larson is hopeful that change is on the horizon as private PET/CT clinics vocalize their frustrations with the status quo.

PACS isn’t the only challenge in the hybrid world. Training of both physicians and techs is tricky. “PET/CT has raised all sorts of questions like who is best-trained to read PET/CT studies—radiologists or nuclear medicine physicians?” notes Larson. A similar conundrum is evident with techs as a PET/CT tech should be licensed in both modalities. The good news is professional organizations are tackling the challenge and answering the tough questions about standards, training and competency assurance.

Larhs of Tacoma Radiology Associates envisions the advent of medical imaging of oncology rather than the subset of radiology and nuclear medicine. The specialty implies PET/CT and training in radiology and nuclear medicine for physician-interpreters and techs, he says.

The next frontier: Tumor response

The real promise of PET/CT could be right around the corner. “In the future, we won’t do first-class cancer therapy without PET/CT,” predicts Busch. One class of upcoming applications is therapy response. When PET first hit the imaging arena, patients were scanned after three to four cycles of medical therapy or radiation oncology. Today, some patients are scanned after the first cycle. The results allow physicians to change a therapy that isn’t working, or stop therapy altogether if no benefit is seen. On the other hand, a scan can confirm successful treatment. Take for example the ovarian cancer patient whose PET/CT showed tumor markers in the normal range, allowing her oncologist to prescribe a “break” from chemotherapy. This has a positive quality-of-life impact on the patient and alleviates the need for expensive chemo treatments. Similarly, physicians can prognosticate the outcome of radiation oncology for a lung cancer patient within a matter of weeks. Unlike a traditional CT, which does not discern active lymphoma, PET/CT can detect whether or not active lymphoma is present to determine if a lung cancer patient is a surgical candidate.

At Memorial Sloan-Kettering, treatment response goes beyond the clinical and incorporates treatment development. “A number of companies want to incorporate PET/CT into their treatment monitoring algorithms,” confirms Larson. In either case, PET/CT holds the potential to reinvent oncology care. “PET/CT is more than wishful thinking or hope. It produces data,” Busch says. That data can help optimize treatment and spare patients from needless surgery, a tidbit that third-party payors will appreciate, too. “We will see the day when third-party payors refuse to allow separate scans and insist on PET/CT in one shot,” predicts Busch. That is a welcome forecast for practices wrangling with the impacts of diminished reimbursement.

Still, deploying PET/CT to monitor therapy can be tricky. “We’re dealing with a heterogeneous disease. Tumor response differs for different cancers and in radiation therapy and medical treatment,” explains Busch.

The hybrid future

While treatment response is the rage in nuclear medicine and oncology circles, it isn’t the only upcoming development in PET/CT. Larhs points to “tremendous interest” in approving PET/CT for infection imaging, namely fever of unknown origin. “Infection is a cousin of cancer, and there is no good, single imaging method to diagnose infection,” explains Larhs. Infection could obtain CMS approval by the end of 2007.

New tracers also are in the works as FDG is one of hundreds of potential tracers, but it is very expensive to investigate and market a new tracer. Still, Larson predicts growth in the radiotracer market. For example, certain tracers may help tailor treatment by determining if a tumor is susceptible to a particular drug. Another area of growth is radio-labeled antibodies, which could ease detection by facilitating quantification and boosting sensitivity. “This technology is by no means completely mature,” concludes Larson.

The hybrid evolution at a glance

PET/CT continues to have a major impact on practice of oncology. The combination of anatomy and function provides physicians with the data needed to more accurately stage cancers, and, more recently, determine the effectiveness or appropriateness of a particular treatment. Each advance delivers multiple benefits; with accurate data, patients are more appropriately treated, which saves time and money and lives. And the technology continues to evolve as practitioners look forward to improved image management and review systems. New tracers promise to help further tailor treatment.