Focused radiation continues to be an effective means to treat cancerous tumors, particularly when there is a clear-cut shot at the target. Finding that shot, however, is no simple task for clinicians for several reasons; the target is often surrounded by healthy tissue, it can grow, shrink or shift over time, and it is affected by changes in the patient’s anatomy.
The Hi·Art® treatment system, a radiation therapy device that uses 3D CT imaging, was developed by TomoTherapy Inc., Madison, Wis., to address this challenge. The device leverages the ring gantry geometry used in CT scanning to deliver intensity-modulated radiation therapy (IMRT) from all angles around the patient, with minimal side effects.
Graham Reitz, Research Engineer, says “Most cancer centers and medical providers now know the need for image guidance. Our co-founders, Rock Mackie and Paul Reckwerdt, got together 17 years ago at the University of Wisconsin to mount the linear accelerator of the Hi·Art® device on a ring gantry. This configuration allowed helical fan-beam delivery of IMRT, with integrated megavoltage CT imaging. The advance lets clinicians better focus radiation beams and treat the most complex cases.”
Essentially, a patient lays on a table or couch that slides into the gantry. Once in, the gantry rotates 360º to deliver IMRT that uses tens of thousands of narrow beamlets, all targeting the tumor and individually set to contribute to the total tumor dose. A DMC-2153 5-axis controller from Galil Motion Control handles the X-Y-Z motion of the couch. It places the table to an accuracy of +/- 1 mm. TomoTherapy is moving toward sub-millimeter accuracy in future models.
The X-Y-Z motion of the couch in the TomoTherapy CT imaging system is controlled by a DMC-2153 5-axis controller from Galil Motion Control to within +/-1mm accuracy.
“We considered several motion controllers and Galil’s met our requirements for its Ethernet-based control of step and servo motors, ability to multitask, SSI feedback capability and robust programming language,” added Reitz. “It also was small enough to fit in our very small space.”
The controller’s PID compensation feature controls the Z-axis for the up and down motion of the couch. An integrated motor and step driver work with the DMC-2153 to control the Y-axis to move the couch in and out of the bore, and the X-axis for right and left lateral movements.
The controller accepts two forms of feedback, incremental and SSI absolute, to check and maintain the couch position should there be any disruption from a power loss, and to ensure precise synchronization of the X-Y axis.
“Along with integrated CT guidance,” said Reitz, “the two key differentiators of our systems over
conventional systems are the ring gantry design for helical delivery, and our binary multi-leaf collimator for beam shaping and modulation.” He explains that since the width of the helical fan-beam IMRT sent to the axis is 40 cm, and that maximum couch length is 160 cm, very large volumes can be treated in a single, simple set-up. In fact, it is possible to treat anywhere within a cylindrical volume of 40 cm in diameter by 160 cm long. Even larger diameter volumes can be treated with fewer beams.
Typically, tens of thousands of beamlets are included in a precise treatment. A single beamlet corresponds to the radiation emitted through an open leaf of the system’s patented Multi-Leaf Collimator (MLC) with the gantry at any given angle, during any given rotation. The need for a large number of beam angles to achieve a highly-conformal dose distribution is much like the need for a large number of image projection angles in CT imaging.
The DMC-2153 is an integrated motor and step driver that accepts two forms of feedback, incremental and SSI absolute, to check and maintain the couch position and to ensure precise synchronization of the X-Y axis.
Lane Rosen, MD, Director, Radiation Oncology at Willis-Knighton Cancer Center, Shreveport, LA, explained the benefits of this approach: “The TomoImage™ capability gives you better visualization and accuracy of patient position than the step-and-shoot systems, while the delivery of the helical treatment provides better coverage and conformality of the target than with previous rotational IMRT systems.”
In addition, Galil engineers customized the controller so it could easily accept all of the SSI devices for feedback. The I/O manages data for machine shutdown, clutch status, and emergency stops. It also sends signals to its embedded computer for motion calculations while the TomoImage’s Linux computer calculates, coordinates and talks directly to the Galil controller to provide redundancy and better safety.
Today, TomoTherapy has over 150 Hi·Art® treatment systems installed at clinics around the world, treating tumors of prostate cancer, lung metastasis, scalp carcinoma, multiple lesions and more.
Galil Motion Control
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