Radiation Oncology Imaging Grows Up

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BrianLab’s ExacTrac X-Ray 6D image-guided radiation therapy systemRadiation 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,