3D Volumetric Imaging Enhances RT Treatment Planning

PHILADELPHIA—A device that displays a holograph-like 3-dimensional (3D) image, created from a CT, MRI, or PET dataset, holds promise for more accurate radiotherapy treatment planning (see image on page 1). James C. H. Chu, PhD, professor of radiation oncology, Rush University Medical Center, presented results of a pilot study of the Perspecta Spatial 3D System, developed by Actuality Systems, Inc. (Bedford, Massachusetts), at the 48th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (abstract 2810).

"Many of the tasks involved in radiotherapy treatment planning are 3D in nature, such as volume delineation, beam placement, and plan evaluation," Dr. Chu said, "but current planning displays are 2D in nature." Even 3D renderings must be displayed on a flat computer screen, he said, and may require goggles to get the 3D effect.

The Perspecta Spatial 3D System produces 3D anatomic images by projecting multiple cross-sectional images (using DLP technology from Texas Instruments, Inc) at a rate of 6,000 frames per second onto a screen rotating rapidly at 900 rpm. "The screen is spinning continuously and the image on the screen is changing continuously. Because the screen is spinning so fast and the image is changing so fast, your eye and brain integrate all the individual cross-sections into a 3D object," Dr. Chu told ONI.

The resulting semi-transparent 3D image appears to float in space within a 24-inch dome, allowing a full 360-degree field of view (Figure 1). For radiotherapy treatment planning, the radiation dose distribution can be superimposed on the 3D Perspecta image and viewed and manipulated from any point around the dome.

The Perspecta technology was invented by Gregg Favalora, who launched Actuality Systems from his basement apartment in 1997. He currently serves as chief technical officer of the company. In addition to medical uses, including molecular engineering for drug discovery, the technology is being used in other fields, including oil and gas exploration and by NASA to analyze earth science and astronomical data.

Study Results

Dr. Chu's study compared radiotherapy treatment plans produced on a conventional flat computer screen with those prepared using the Perspecta Display. Fourteen plans that had been used previously to treat cancer patients were replanned by two different planners, one using only conventional 2D imaging of CT scans and the other using 2D imaging plus Perspecta 3D imaging. The quality of the plans was then reviewed by four physicians who were blinded as to the planning device used.

More than half of the plans for the 14 cancer patients (12 brain, 1 lung, and 1 breast) came from Rush University, and the rest were provided by the other participating institutions, Tufts-New England Medical Center, Boston, and Rhode Island Hospital/Brown Medical School, Providence, Dr. Chu said.

The reviewers rated 6 of the 12 brain cancer treatment plans using Perspecta as better; 4 of the plans were rated as equivalent; and in 2 cases, the plans generated by conventional 2D imaging were rated better. In the lung cancer and breast cancer patients, the Perspecta-generated plans were rated better than those produced with conventional imaging.

All reviewers felt that the Perspecta device allowed better appreciation of 3D relationships of anatomical and dose data than images from a flat screen display. The location and size of over- or under-dosed regions were also easier to identify on Perspecta, Dr. Chu said.

"Our study found that the Perspecta Display provides users complex information in a more efficient and natural way," Dr. Chu said. "Perspecta allows you to see the 3D structure (Figure 2) much more clearly than a conventional imaging display." Dr. Chu said the study will include 30 patients in the next phase, with patients more evenly distributed among the three participating institutions, and will cover a variety of cancer sites (eg, prostate and head and neck).

Dr. Chu said he expects the device also to be useful in radiotherapy delivery and in surgical planning. "For example, in breast cancer patients, often the location of a small tumor as shown on the mammogram doesn't correlate well with the patient on the surgical table," he said. "The Perspecta device could perhaps be used in the surgical suite to help the surgeon locate the tumor accurately."