AAPM: Researchers develop hybrid linac/MRI
Researchers at the University of Alberta's Cross Cancer Institute are developing a new technology that integrates linear accelerators, or linacs, and MRI systems. The group will discuss their findings at the 2009 American Association of Physicists in Medicine (AAPM), which takes place this week in Anaheim, Calif.
The proposed hybrid linac/MRI system seeks to help doctors treat certain types of cancer by allowing them to monitor soft-tissue tumor movement--such as the liver, lungs or prostate--in real time during radiation treatment. Though the new technology is not yet available in the clinic, Canadian scientists have demonstrated its feasibility.
Modern cancer radiotherapy often depends on how well radiation oncologists and medical physicists can determine the location and shape of a tumor. When doctors plan radiotherapy treatment, they first define the outline of target tumors by collecting 3D images. Physicians now can define the edges of many tumors to within a fraction of an inch, according to the researchers. Due to tumor movement, radiation is delivered to the area surrounding the tumor to ensure that it is always in the beam's sight. Therefore, adjacent normal tissue as well as critical organs may receive a radiation dose.
B. Gino Fallone, PhD, director of medical physics at the Cross Cancer Institute, said that image-guided radiotherapy (IGRT) is the latest way of doing what radiologists have always done.
"Track it and treat it," he said. "That's been the goal of radiation oncology for 50 years."
While existing IGRT techniques are effective, they are limited because they do not give true image-based guidance of the entire volume of the tumor, according to Amit Sawant, PhD, from the department of radiation oncology at Stanford. Instead of imaging the whole anatomic volume containing the tumor,markers and seeds provide a few points in space that doctors can follow, which Sawant calls "faith-based radiation delivery."
With CT, it is often difficult to distinguish tumors from normal tissues. Researchers said that MRI provides superior distinction between normal and cancerous tissues, but the technology has not been available to place an MR scanner in the treatment room. They reported that a more robust way to guide radiotherapy would be to image the entire tumor continuously and adjust the radiation beams accordingly.
Fallone and his colleagues are testing a prototype linac/MRI system. Linacs use radio waves to accelerate electrons to high speeds and crash them into a solid metal target--typically tungsten--producing high-energy x-rays in the collision.
According to the investigators, the x-rays destroy cancerous cells by causing irreparable damage to the cells' DNA. MRI systems are successful at imaging soft tissue and could be ideal for combining with linacs because cancers occur in soft tissue. However, they found that the problem is making MRI systems and linacs work together. Linacs emit radio waves, which interfere with MRI hardware, while MRI magnets can interfere with linac systems.
Fallone and colleagues have built a prototype linca/MRI device that overcomes the obstacles to integrating the two technologies--making it the first working system to do so.
In December 2008, they performed experiments with the system and produced MRI test images with the linac on and off to demonstrate that interference is eliminated. A working, clinically-ready system is not here yet, but Fallone said it will be in five years or so.
In related research being presented at AAPM this week, Sawant's group from Stanford University in Stanford, Calif., is determining specifications on how the new technology can be used
Sawant, and Stanford colleagues Kim Butts Pauly and Paul Keall, have been working on the technical details of how a linac/MRI system could be used to achieve real-time image guidance. Sawant said their goal is to achieve performance at least ten times faster than a traditional MRI. They are developing imaging specifications for a system to image the entire volume of a tumor in real time, about three times per second.
The proposed hybrid linac/MRI system seeks to help doctors treat certain types of cancer by allowing them to monitor soft-tissue tumor movement--such as the liver, lungs or prostate--in real time during radiation treatment. Though the new technology is not yet available in the clinic, Canadian scientists have demonstrated its feasibility.
Modern cancer radiotherapy often depends on how well radiation oncologists and medical physicists can determine the location and shape of a tumor. When doctors plan radiotherapy treatment, they first define the outline of target tumors by collecting 3D images. Physicians now can define the edges of many tumors to within a fraction of an inch, according to the researchers. Due to tumor movement, radiation is delivered to the area surrounding the tumor to ensure that it is always in the beam's sight. Therefore, adjacent normal tissue as well as critical organs may receive a radiation dose.
B. Gino Fallone, PhD, director of medical physics at the Cross Cancer Institute, said that image-guided radiotherapy (IGRT) is the latest way of doing what radiologists have always done.
"Track it and treat it," he said. "That's been the goal of radiation oncology for 50 years."
While existing IGRT techniques are effective, they are limited because they do not give true image-based guidance of the entire volume of the tumor, according to Amit Sawant, PhD, from the department of radiation oncology at Stanford. Instead of imaging the whole anatomic volume containing the tumor,markers and seeds provide a few points in space that doctors can follow, which Sawant calls "faith-based radiation delivery."
With CT, it is often difficult to distinguish tumors from normal tissues. Researchers said that MRI provides superior distinction between normal and cancerous tissues, but the technology has not been available to place an MR scanner in the treatment room. They reported that a more robust way to guide radiotherapy would be to image the entire tumor continuously and adjust the radiation beams accordingly.
Fallone and his colleagues are testing a prototype linac/MRI system. Linacs use radio waves to accelerate electrons to high speeds and crash them into a solid metal target--typically tungsten--producing high-energy x-rays in the collision.
According to the investigators, the x-rays destroy cancerous cells by causing irreparable damage to the cells' DNA. MRI systems are successful at imaging soft tissue and could be ideal for combining with linacs because cancers occur in soft tissue. However, they found that the problem is making MRI systems and linacs work together. Linacs emit radio waves, which interfere with MRI hardware, while MRI magnets can interfere with linac systems.
Fallone and colleagues have built a prototype linca/MRI device that overcomes the obstacles to integrating the two technologies--making it the first working system to do so.
In December 2008, they performed experiments with the system and produced MRI test images with the linac on and off to demonstrate that interference is eliminated. A working, clinically-ready system is not here yet, but Fallone said it will be in five years or so.
In related research being presented at AAPM this week, Sawant's group from Stanford University in Stanford, Calif., is determining specifications on how the new technology can be used
Sawant, and Stanford colleagues Kim Butts Pauly and Paul Keall, have been working on the technical details of how a linac/MRI system could be used to achieve real-time image guidance. Sawant said their goal is to achieve performance at least ten times faster than a traditional MRI. They are developing imaging specifications for a system to image the entire volume of a tumor in real time, about three times per second.