BOSTONFor the cancer patient who can’t hold a
breath or stay still during radiation therapy, a team of medical experts and
engineers is working on a tracking solution worthy of James Bondspy cameras
and robotic vision.
Andre Kalend, PhD, of the University of Pittsburgh Medical
Center, described the Robotics Artificial Vision (RAV) system at the 42nd
annual meeting of the American Society for Therapeutic Radiology and Oncology
RAV "anticipates" slight movements, such as tremors,
breathing, coughing, and sighing. Then, by moving the treatment table, it
realigns the patient for more precise delivery of radiation beams or alerts the
operator in time to halt therapy until the movement stops.
"The accelerator itself can ‘see’ the patient,
recognize the patient’s skin anatomy, and treat only when the robotic eye
sees that the patient is in alignment with the isocenter of the beams,"
Dr. Kalend told ONI (see Figures 1 and 2). The full RAV-Venturi system can
distinguish normal breathing from movements triggered by normal physiologic
A radiotherapy medical physicist, Dr. Kalend developed the RAV
system prototype with Joel Greenberger, MD, chairman of the Department of
Radiotherapy at the University of Pittsburgh Medical Center, and Takeo Kanade,
PhD, of the Carnegie Mellon University Robotics Institute, also in Pittsburgh.
The group began work 5 years ago on ways to make radiotherapy
more dynamic and more accurate with respect to the tight target margins
required for 3D conformal radiation therapy and intensity modulated radiation
Cancer patients are often weak, Dr. Kalend said, and cannot
tolerate today’s invasive respiration-gated treatments. Tracking breathing is
important, however, because the margins of error for precision beams are so
small that coughing, sniffing, sneezing, or burping can cause misalignment.
A Wobbly Dart Board
"Radiation beams and fields are tailored to the irregular
shape of the mobile tumor with margins no longer of single centimetersnow it’s
a few millimeters," Dr. Kalend said. With this small margin of error, he
said, "the patient, the target, is like a wobbling dart board."
He summarized his thinking behind RAV as, "If I can’t
stop [movement], I must be able to track it. If it’s normal, I treat; if it’s
abnormal, I stop." To do that, he equipped the accelerator with
"vision" or "eyes" to see patient movement and
"ears" to hear the patient breathe.
The System’s Eyes
RAV has eight independently operating cameras that serve as
eyes. They are mounted on the walls of the treatment room and the accelerator.
The cameras use patented technology called CCD-based Robotics Vision Tracking
to lock alignment lasers from the accelerator onto the patient’s natural skin
features or standard radiotherapy tattoos (see Figure 2).
Dr. Kalend stressed that CCD tracks patient anatomy rather than
the treatment table (traditional mechanical
fixtures). He calls this process "virtual fixation" as opposed to
traditional "mechanical fixation."
Like a cruise missile, he said, the system finds its targets
via image, or shape, matching, rather than alignment via x,y,z coordinates. The
RAV system homes in on the target (the patient’s skin rather than a missile
target) and only "fires" when the image matches that of the radiation
therapy treatment plan. To get that match, the automated treatment table
responds like a joystick to video commands to move and rotate until the
alignment is correct.
The System’s Ears
The Venturi "ears" of the system listen for the
patient’s laryngeal Venturi waveforms, made by the jet streams of air passing
through the lower orifice of the larynx, to distinguish normal breathing from
Tumors in the lung and abdomen are mobile and deform with
breathing; consequently, they are almost impossible to target with precision
conformal radiation therapy or IMRT beams. Dr. Kalend and a third-year
University of Pittsburgh medical student, Kenneth Clark, last year invented the
Venturi respiration tracking system.
It is sort of an FM stethoscope that tunes in and listens to
the patient breathing, and gates the radiation machine to fine beams that are
on only during very specific breathing cycles or phases of the patient
breathing freely under treatment, Dr. Kalend said.
This summer, Dr. Karen Shimoga from Carnegie Mellon University
joined Dr. Kalend, and together they are perfecting the Venturi’s FM wave
tuning decision logic so that it operates faster than a single accelerator beam
The first treatment session is basically a learning session,
during which RAV learns the normal sequence of movements and skin
characteristics of the patient.
The system studies how a person coughs and learns the
"signature of coughing," he said, as it affects the position of the
"We know that no matter how you constrain the patient from
breathing, natural respiration urgeslike swallowing, coughing, sniffing, and
even just lifting a leg or taking a deep inspiration differentlyaffect the
position of the diaphragm and therefore throw out your beam port
position," he explained.
Dr. Kalend set four requirements when his group began
developing the RAV-Venturi technology, he said. The system had to be
noninvasive, competitive economically, accommodate patients who could not hold
their breath for 12 seconds, and operate in real time.
In benchmark studies, RAV is reported to have achieved an
alignment accuracy of 2 mm (limited by the width of the laser) and 0.95
tracking correlation with Venturi interrupts measured in milliseconds, Dr.
So far, the system has been tested on volunteers, and the group
has applied for NIH funding for a clinical trial with Internal Review Board
approval to start testing the system in patients during actual radiation