Big Steps Towards Dual Energy Simulation
Martin Suter | 2015-08-24
For the radiation oncology team, fast acquisition offers the unique chance to scan organs in motion.
In oncology, Dual Energy CT yields excellent results not only for diagnostic purposes. David Roberge, MD, at the University of Montréal in Canada, optimizes radiation therapy by utilizing Siemens’s big bore scanners with Dual Energy capabilities.
Energy seems to be what David Roberge is all about. Below the desk of the fast-talking oncologist, a wastebasket overflows with empty coffee capsules. He consumes “rarely less than three” cups a day, Roberge confesses. Yet stress is not what drives the Head of the Department of Radiation Oncology at the Centre Hospitalier de l’Université de Montréal (CHUM).
Rather, Roberge is animated by Dual Energy. The 41-year-old French-Canadian is convinced that using computer tomography scanners with Dual Energy capabilities can improve radiation treatment of cancer patients. Together with the 23 radiation oncologists in his department he has embarked on an ambitious Dual Energy CT research program.
“The whole work that will hopefully produce benefits because Dual Energy is just starting right now,” he says. Barely suppressing his pride, he adds: “We are pioneers.”
Dual Energy scanners take two images at different energy levels of typically 80 kV and 140 kV. They are routinely used in clinical settings to improve the visualization of conditions like musculoskeletal injuries, gout, arteriosclerosis, stroke, pulmonary embolism, brain hemorrhage, and cardiovascular disease. “Take a kidney stone,” Roberge explains, “it will tell you the composition of the stone, and this helps you find the disease that creates the stone.”
Taking technology a step further
When it comes to cancer, the advantages of acquiring two different CT images have been proven for the diagnosis of a variety of tumors, mainly those in soft tissue. Lesions in the liver or the pancreas are more clearly identifiable as benign or cancerous because they look different at various CT energy levels.
David Roberge and his team take the technology a step further: They believe Dual Energy CT images allow them to more precisely simulate external and internal radiation therapy as well as to improve dose calculation. To prove the concept – and offer patients better treatment – the department purchased three state-of-the-art Siemens CT scanners. One of them, the Dual Source SOMATOM Definition Flash, has two separate X-ray tubes capable of producing two images at different energy levels in one go. The other two scanners, both SOMATOM Definition AS Open, run two consecutive scans to acquire Dual Energy data.
Radiation therapy simulations
Both Siemens radiation therapy tailored scanners boast wide bores of 78 cm for the SOMATOM Definition Flash and 80 cm for the SOMATOM Definition AS Open. This makes them ideally usable as radiation therapy simulators. In order to plan for radiation treatment, patients are positioned exactly as they will be on the table of the linear accelerator. “For instance, breast cancer patients must be scanned with one arm up,” says Roberge. “Plus we need to see all of the tissue, not only the tumor. We need a bigger image. Also, we need a flat table enabling a reproducible position and lasers for reference marks.”
David Roberge cannot show the two single-source scanners, because they are yet to be installed at a new facility of the CHUM. A private consortium is in the process of building three glass towers near Montréal’s Quartier Latin. The government-run hospital as the tenant will move in gradually, and the most services, including radiotherapy, will be operational 2016, the final project (including an auditorium, offices and all of the clinic space) will be operational in 2020. For its interior design, Roberge made sure the scanning and radiation equipment will be mounted in a workflow-optimizing layout, with CT scanners, MRI scanners, and injection rooms all in a row.
The Dual Source scanner, however, has been in operation in CHUM’s old building for about a year. The brick architecture of the Hôpital Notre Dame at the east end of the Parc Lafontaine looks as plain from the outside as it is impractical on the inside. The Radiation Oncology Department has gone though serial expansions and has had to function over three levels, requiring time-consuming patient travel between floors. It is expected that the new building will simplify procedures considerably.
The present locality cannot diminish Roberge’s enthusiasm for the Dual Source Dual Energy scanner. Its purchase became one of his priorities after he took over the department four years ago. Born in Montréal, David Roberge became interested in radiation therapy in medical school, when his grandmother was suffering from Hodgkin’s Disease. The fascination has never left, and he passed it on to his colleagues at CHUM: Roberge could convince his fellow radiation oncologists to each contribute about 10,000 Canadian Dollars of their private funds to the hefty purchase price of the SOMATOM Definition Flash.
In Canada’s socialized medical system the doctors do not expect to increase profits, he says. “But there is a feeling that it will help the image of the institution to have this equipment. It also helps when we ask patients for money to support the institution.” The idea is to make CHUM better known outside of Québec. The Dual Source Dual Energy scanner is “a large piece of equipment that was bought with goals beyond giving the best care for patients,” Roberge explains. “When we got that device we were getting something that was uncommon, that has possibilities for the future, that we can use to innovate with, that gives us research opportunities.”
Dual Energy CT can provide patient-specific tissue information such as effective electron density (ρ eff Fig. 1A) and effective Atomic Number (Z eff Fig. 1B).
Tailored treatment of tissue
Most of the benefits of Dual Energy CT’s can be achieved with either of the two scanner types. Acquiring two scans at unequal energy levels helps reduce metal artifacts, those X-ray shadows cast by implants. Another promising area of research is the tailored treatment of tissue based on functional information. “Usually we think of healthy tissue on a volume basis,” Roberge says. He takes the example of the lung, where radiation treatment is considered safe if it does not affect more than, say, a certain percent of the organ’s 1,000 cubic centimeters. In that regard, lungs, kidneys, or livers “are considered a piece of meat.”
But in reality not all parts of the lung are equally active. “If patients have been smoking for many years and they have underlying lung disease, some parts of the lung might be contributing more to the respiratory function and some less,” David Roberge explains. The aim is to irradiate the different areas of the lung unequally and, if possible, avoid as much as possible treatment beams going through healthy and functionally active parts. This is where Dual Energy comes in. “It allows us to automatically quantify the iodine that is in the contrast material,” says Roberge. “In many cases we think the amount of iodine correlates with the function. So we have a project looking at a lung with a Dual Energy scan and quantifying lung function based on contrast.”
Potential to open up new approaches in radiation therapy
As Roberge explains, Dual Energy can improve image quality with iodine contrast. “But to calculate the dose we must look at the body without contrast. We typically did one scan without contrast and then injected contrast and did it again. And we used one to define the target and one to calculate the dose. We hope to come up with a methodology to use the Dual Energy to do the scan just once with the contrast and to use software to remove the contrast for the dose calculation.” As a result, the second scan would be unnecessary. “It will mean less radiation dose for the patient, and it is also faster.”
“Exact dosing is particularly important with brachytherapy, because often larger doses are delivered internally than externally,” Roberge says. “If we can better define the tissues and their electron density, that is, how much radiation tissue can absorb, with Dual Energy, maybe it will have an impact in brachytherapy dose calculation.” Dual Energy promises even better results for proton therapy, he believes. “But there is currently no proton therapy in my neck of the woods.” Canada’s healthcare system affords only one proton accelerator in Vancouver. In the United States, 13 of the very expensive machines are in use.
Again and again, Roberge returns to his SOMATOM Definition Flash. Its advantage beyond the Dual Energy capability is image quality and speed. Hélène Lama, a radiotherapy technician, is full of praise for the SOMATOM Definition Flash scanner. “Acquisition of the image is faster and the definition of the image is really, really good,” she says. Patients can be intimidated by the large size of the machine. “Some are claustrophobic. Then we talk to them and explain that the machine is there to help them.”
For the radiation oncologist, fast acquisition offers the unique chance to scan organs in motion. “We have seen things we did not imagine,” says Roberge. “For example, CT scans where you see someone swallowing, displayed in a video.” Looking into the future, the caring father of a young daughter can visualize highly specific radiation treatments of critical organs such as the pulsating heart. Aided by fast Dual Energy CT images, the therapeutic radiation could eventually be applied “only at one point in the heart’s cycle, for instance at maximum dilation.”
But Roberge knows that such innovations take time. “Proving the concept can be achieved soon, but the clinical proof will only be possible later.” The slow rhythm of research does not discourage him, though. The additional information provided by Dual Energy CT, particularly with fast single sourcing, has already yielded the most important results for any physician, he says. “It has changed how we treat certain patients.”
About the Author
Martin Suter, based in New York City since 1993, is a correspondent for the Swiss Sunday newspaper, Sonntags - Zeitung and has written for a variety of major European publications on topics ranging from politics and technology to business and healthcare.
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