Varian Medical Systems has received FDA 510(k) clearance for patient position monitoring capabilities that have been added to its RPM respiratory gating system, which is used to synchronize imaging and radiation therapy treatment with a patient’s respiratory cycle. The new feature in Varian’s RPM system detects any motion that compromises the accuracy of the treatment, according to a release.
The RPM system works by placing a reflective marker box on the patient's chest or abdomen and monitoring its motion using special cameras positioned in the treatment room. The previous system monitored the motion of the marker block only in the vertical dimension, to correlate it with the rhythmically repeating tumor motion that occurs as the patient breathes, and to trigger the treatment beam on and off as the tumor moves in and out of range. The new version of the RPM system analyzes the marker block motion in all three dimensions as it moves up and down, forward and back, and side to side. A new display on the system’s console immediately alerts the radiation therapist if the patient moves and should be repositioned, Varian said.
“The system actually learns, for each patient, how the marker block is going to move when that particular patient stays still and breathes normally,” said Mika Miettinen, product manager for the RPM system. “If the patient shifts on the treatment couch in any direction beyond the natural range of motion, the system alerts the clinician to halt the treatment and reposition the patient.”
“Immobilization—especially for moving tumors in the thorax—is never perfect. Patients are not locked down; they have some freedom to move,” Miettinen added. “With this new version of the RPM gating system, if a patient moves, the therapist will know it.