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Anatomy Modeling in Less Time

Improved anatomy modeling tools let physicians share the workload—with their software

Radiation oncologists are in short supply in many parts of the world. In the United States and other countries, they work long hours to keep up with the growing number of cancer patients resulting from the aging of the baby boom generation.

Sitting at a computer screen and tracing the targets and the organs at risk onto CT images, slice by slice, can be time-consuming work for physicians. Often taking hours for complex cases, it is the longest step in the radiation treatment planning workflow. “Our radiation oncology residents often spend four or even six hours on target definition and anatomy modeling of head and neck cases or other cases where the contrast is low,” reports Andrew Lukban, chief physicist at New York’s SUNY Downstate Medical Center. “Anatomy modeling is the gating factor in our department productivity.”

To relieve the bottleneck and free up doctors’ time, dosimetrists or medical physicists in some departments may do preliminary outlining of high-contrast structures, such as the liver, prostate, and skin, before the radiation oncologist takes over. However, in 2003 the ASTRO workforce committee reported a shortage of these radiation oncology professionals as well, and many practices are feeling the impact of that shortage today. Regardless of attempts to share the workload of anatomy modeling, the heavy lifting of delineating targets and contouring low-contrast structures, such as shadowy lymph nodes, remains the responsibility of very busy radiation oncologists.

Improved anatomy modeling tools are needed to speed the treatment planning workflow, increase department productivity, and free doctors to spend more time with patients. “The largest problem is the lack of time for the oncologists,” says Ulf Isacsson, PhD, a medical physicist at Sweden’s Uppsala University Hospital. “So I should say that better tools for defining targets and organs at risk quicker would be a solution that should help us a lot.” Uppsala has four linacs, a high-dose-rate (HDR) brachytherapy afterloader, and a proton facility. Clinicians there treat approximately 1,200 patients a year with radiation therapy, and they use Oncentra to plan both external beam and brachytherapy treatments.

A “pearl” of a contouring tool

Lukban points to Oncentra Anatomy as a new-generation contouring solution. SUNY Downstate uses the platform-independent Oncentra treatment planning system to plan intensity-modulated radiation therapy (IMRT) and other external beam treatments, as well as HDR brachytherapy. “We have a residency program, and our residents work at five hospitals in New York City, where they get to experience different treatment planning systems. It was our residents who were the main proponents for Oncentra Anatomy because they found that it helped them to contour faster,” recalls Lukban. “We have been using the new Oncentra Anatomy tool for about seven months, and the residents are doing modeling in half the time.”

To speed up contouring, Oncentra Anatomy provides a “pearl” tool, a round contouring cursor that is popular with users because it is so easy to use. The boundary of the pearl can be expanded close to the size of the organ being contoured. “If you hold the mouse button down and move the mouse, the edge of the ball will trace around no matter where you go,” explains Lukban. “It allows you to fill in the entire structure very quickly. You can expand the diameter of the pearl with the arrow keys and almost just wobble it to fill in the boundaries of the structure instead of marking point by point.” This is just one of the many streamlined modeling features of Oncentra Anatomy, which can be configured as a standalone module and connected to virtually any DICOM-compliant treatment planning system.

Automation is key to speed and consistency

“It’s good to have more efficient drawing tools, but if you can get the job done more automatically, you can make the whole process go faster,” says Lukban. That is the impetus behind model-based segmentation (MBS), a new feature of Oncentra Anatomy. Oncentra MBS lets planners start with an organ model and parameters selected from a library. Then the automatically generated contours can be stretched asymmetrically in three dimensions with a single mouse operation. “To correct the contours in three dimensions in this way is a much faster way than we could do with previous tools,” says Kristina Nilsson, MD, radiation oncologist at Uppsala University Hospital. “I have seen this demonstrated for the prostate, and I think it would be very useful.”

Lukban agrees. “With model-based segmentation you can produce the contours automatically; then all the physician needs to do is to review and make corrections. This would save a lot of time for physicians.”

Lukban sees another advantage of model-based segmentation: consistency. Not all radiation oncologists contour anatomy and targets in the same way. Some plot a series of points and let the planning software connect the dots. Many prefer to draw in the contours themselves because it’s faster. However, drawing with the computer mouse can easily create inconsistencies and anomalies that confound the dose calculation engine.

Consistency is important in another way as well, points out Isacsson. “Consistency in anatomy contouring is desirable for clinical studies and for following up patients,” he explains. “It is important to know that every patient has received consistent treatment. While a tumor varies, other structures, such as lymph nodes, are defined in the same way in every patient. To evaluate patients, you want to know that they have been treated in the same way. Model-based segmentation is a step in the right direction.”

Oncentra Anatomy, with advanced tools for contouring and model-based segmentation, is now available. Radiation oncology centers worldwide use Oncentra, the independent treatment planning system, to plan brachytherapy, IMRT, IGRT, and proton beam treatments. For more information about Oncentra innovations, contact your Nucletron representative or visit http://www.oncentra.info/.