Radiation Oncology Imaging Grows Up

Radiation oncology imaging has come of age. New imaging options — cone beam CT, 4D CT, PET-CT and more — are showing promise in the treatment planning and delivery realms, enabling radiation oncologists to plan and deliver razor-sharp treatment. Lung cancer patients are benefiting from ultra-precise respiratory gating, and other populations could see improvements via image-guided adaptive radiation therapy (IGART).

"Ten years ago, radiation oncologists were thrilled to receive a hand-me-down CT scanner from the radiology department," recalls John Bayouth, PhD, director of medical physics for the department of radiation oncology at University of Iowa Hospitals and Clinics in Iowa City.

But the days of making do with secondhand imaging equipment are ancient history in many radiation oncology departments; the new department hums and buzzes with a variety of state-of-the-art imaging equipment fine-tuned for the specific needs of radiation oncology. The objective in radiation oncology remains the same as always: to maximize tumor dose and minimize collateral (a.k.a. normal tissue) damage — but the means of achieving that objective are becoming increasingly sophisticated.

Radiation oncology imaging solutions fall into two categories: those that provide more precise treatment planning images and systems that facilitate increasingly accurate treatment delivery. The advent of IGART ups the ante. IGART uses daily imaging to optimize treatment by changing radiation beam based on anatomical changes over time.

This month Health Imaging & IT visits with several state-of-the-art radiation oncology departments to learn about the promise of new systems, identify strategies for improvement and discover where radiation oncology imaging might be headed in the next few years.  


Inside the state of the art radiation oncology department

The University of Iowa radiation oncology department relocated to a new facility last year. The new filmless, paperless department houses a host of new imaging equipment including a Siemens Medical Solutions Sensation Open 40-slice CT scanner. The large bore scanner is uniquely suited to radiation oncology, says Bayouth, because it enables radiation oncologists to acquire 0.6 mm slice images over a large volume of the patient to accurately delineate the edges of tumors. "The scanner produces sharp images with less contrast and noise than previous systems," explains Bayouth.

Washington University of St. Louis in Missouri has had similar success with Philips Medical Systems Big Bore and Brilliance 16-slice CT scanners. "These scanners are very spatially accurate, and digital values can correlate to radiation dose calculations," explains Dan Low, PhD, director, division of medical physics.

University of Iowa also relies on the Siemens Somatom Sensation 64-slice system to produce 4DCT images to better localize and time treatment. During treatment planning, radiation oncologists compare 2D images to 4D snapshots to reconstruct the tumor and surrounding tissue and pinpoint changes in the size and location of tumors. A better understanding of tumor size and location correlates with more precise treatment, allowing physicians to either up the dose or spare more normal tissue. If a case requires respiratory gating, the team can measure where the patient is in the respiratory cycle and turn the beam on and off accordingly to shrink margins.

"It's a significant improvement over conventional methods," reports Bayouth. The conventional protocol relied on fluoroscopy to image tumor motion. Radiation oncologists either added margins equal to the full range of motion in both the cranial and caudal directions or simply assumed the tumor was at the center of its motion path when the CT was acquired.

"Either way typically entailed treating more normal tissue or missing the tumor," explains Bayouth.

On the treatment delivery side, the department uses four Siemens Encore linear accelerators with electronic portal imaging to image patients prior to or during treatment. The newest tool is Siemens MVision Megavoltage Cone Beam (MVCB) CT Imaging Package, which images the patient prior to treatment to verify the location of the tumor and normal anatomy. "This is particularly important in head and neck cases as patients lose weight and critical structures may move," notes Bayouth.

Cone beam CT is flexing its considerable imaging prowess in facilities around the country. University of California Davis Cancer Center in Sacramento, uses Elekta's Synergy IGRT platform with Elekta XVI cone beam CT to facilitate image-guided treatment management. "The technology provides an opportunity to guide treatment, escalate tumor dose and minimize normal tissue damage," explains Srinivasan Vijayakumar, MD, radiation oncology department chair. Daily image-guided therapy allows physicians to modify treatment every day rather than relying on the same plan for a six- to eight-week course of treatment.
 
The radiation oncology department at Virginia Commonwealth University (VCN) Medical Center in Richmond, relies on an array of imaging and treatment delivery solutions in its dual mission of clinical research and treatment. The inventory includes two Varian Medical Systems Trilogy linear accelerators with the On-Board Imager device for radiographic, fluoroscopic, and cone-beam CT imaging, Varian's PortalVision electronic portal imaging device (EPID) for patient positioning and GE Healthcare's Discovery 16 slice PET/CT scanner employed in conjunction with Varian's RPM respiratory gating system.

Radiation oncology has reached a new stage, says Jeffrey Williamson, PhD, chair, division of medical physics at VCU. "Image-guided radiation therapy (IGRT) is a long-time, well-accepted concept that uses multiple types of radiology studies fused with planning CTs to best identify the target. It's important to deliver what we plan, so we are adding more imaging equipment in the treatment room."

Other essential imaging equipment at VCU includes BrainLAB's ExacTrac X-ray 6D; the system uses high-resolution stereotactic x-rays to pinpoint tumor location while the patient is on the table, robotically repositions the patient as necessary and tracks patient movement. "It's almost like GPS," explains Alan Forbes, MD, a radiation oncologist at MD Anderson Orlando in Florida who also uses ExacTrac. "It allows us to treat precisely and accurately lung lesions we can't see by x-ray," continues Forbes. The system can be combined with superDimension bronchus. The result is real-time, CT-guided electromagnetic navigational bronchoscopy to reach peripheral lung lesions, place a gold marker in the tumor and image the gold marker during treatment for a high degree for accuracy. Accuracy increases with BrainLAB's adaptive respiratory gating module which turns the x-ray beam on and off as the patient breathes in and out, allowing radiation oncologists to have the beam on only when the moving tumor is "at the center of the crosshairs." Forbes has used ExacTrac to treat stage 1 lung cancer with no side effects other than minimal fatigue; the minimally invasive solution also provides a new option for some patients with inoperable lung tumors.

Other patient populations are reaping the benefits of less toxic and shorter treatments, too. The VCU radiation oncology department built an image-guided brachytherapy suite. The new suite is equipped with Varian's Acuity BrachyTherapy Imaging Suite, which includes the Acuity imaging system, VariSource afterloader and BrachyVision treatment planning software. The radiation oncology team uses the system for a one-week course of daily image-guided treatment for breast cancer patients. "Ideally, these patients will have a clinical outcome similar to women who undergo a conventional treatment course," notes Williamson.


Radiology partnerships, auxiliary solutions

Although radiation oncology departments are acquiring imaging equipment at a rapid clip, no department is an island. PET is employed more frequently to stage disease and monitor response to therapy, but not all departments can invest in a PET scanner. In those cases, the radiology department serves as the PET gatekeeper and forms an essential part of the radiation oncology team.

Both PET and MRI play an important supplemental role and the results often change treatment plans. Interdepartmental communication between radiation oncology and radiology is essential, says Benedict, as it's difficult to justify one PET scan for staging and second study for treatment planning. Sharing protocols helps avoid duplicate scans and extra costs.


Looking into the future

"There a lot of ways we are on the cutting edge, but software is not," states Williamson. Consequently, the department relies on a fair amount of home-grown software to fill in the gaps and expand the functionality of its state-of-the-art imaging arsenal. As one of the first sites to deploy large bore CT in IMRT, VCU built its own software and infrastructure for treatment planning. The in-house solution integrates with its Philips Pinnacle treatment planning system. Similarly, the department transfers cone-beam CT images to research software to remove scatter and improve image quality.

On-board imaging is an immature technology; there are few tools and processes to optimize on-board imaging, says Low. Researchers need to determine a plan and destination for the images after acquisition and calculate the human resources required and optimal imaging parameters and frequency to effectively implement on-board imaging, says Low. "On-board imaging is here to stay. It's the main input data for IGART, and its role will be better defined in the future," predicts Low.

Radiation oncology growing pains come in all forms. Washington University of St. Louis, for example, must upgrade its clinical database before it can accept and store cone beam CT images. "We're generating a large amount of data from multiple disparate vendors that needs to be backed up and archived," explains Low. The holy grail, says Low, is a queriable database that can be used as a backup, archive and research tool and manage images, doses, plans and record and verify. It's a tall order that transcends the RT equivalent of PACS.

"Radiation oncology needs more than archiving; we need data management," sums Vijayakumar, who coined the term RT-ADaM (radiation therapy adaptive management system) to summarize the specialty's needs. Currently, UC Davis uses Impac Medical Systems IMPAC image-enabled EMR to integrate images and information and facilitate workflow; Vijayakumar is testing a prototype of the system for data archiving and management purposes. Varian's ARIA Oncology Information System represents another step in the right direction. The oncology specific EMR stores all patient treatment data including images, handles administrative, clinical and financial data and provides information to the entire oncology care team throughout the enterprise.

It is unlikely, however, that any department can rely on a single vendor for all aspects of radiation oncology. "There is no one company that offers it all," notes Benedict. Radiation oncology departments can take some of the pain out of the integration process, says Benedict, by choosing complementary resources that work together.

There are changes on the clinical front, too. IGART remains a work in progress. The radiation oncology department at VCU aims to study cone beam CT and IGART to determine where and how often the 3D reconstructions are best used. "Conventional radiation therapy makes a great plan and sticks to it over the duration of several weeks," explains Williamson. Conventional plans typically use 8 to 20 millimeter margins that increase normal tissue damage. "We might be able to reduce that margin by two-thirds by combining adaptive planning and 4D modeling," predicts Benedict.

Other radiation oncology sites continue to zoom forward and embrace more sophisticated imaging techniques. The University of Iowa currently relies on a Siemens Magnetom Trio 3T MRI for tumor delineation in tumors of the brain, head and neck, breast, liver, pancreas and prostate and may use the system to help assess a patient's response to therapy. Other clinical trials center on spectroscopy in brain tumors. "Spectroscopy provides us an opportunity to understand the morphological nature and molecular elements of tumors," says University of Iowa's Bayouth. Radiation oncologists may use spectroscopy to locate subregions with high populations of aggressive cells or areas less sensitive to radiation. "If we understand the molecular makeup of the tumor prior to treatment delivery, we can use that information to plan therapy," sums Bayouth. The department also plans to install a Siemens biograph 40 PET/CT scanner to help therapists better evaluate patients' response to therapy, identify regions of hypoxia and understand the molecular composition of tumors.


Conclusion

Radiation oncology is virtually exploding with new imaging equipment. Departments are employing a variety of modalities to better define tumors and normal anatomy throughout the course of treatment and to modify treatment based on near real-time position and localization. It's great news for cancer patients as it may up the odds for successful treatment while minimizing the damage to normal tissue. Clinical research and software development are continuing at a rapid clip to help departments make the most of the new technology. Although the RT equivalent of PACS remains on the drawing board it is coming closer to reality. Finally new software to help integrate systems and processes will continue to arrive on the market and simplify and improve the practice of radiation oncology.