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A Simple Method to Monitor Unexpected Patient Movement with Respiratory Gating System

C Liu*, M Axente , J McKay , Erlanger Medical Center, Signal Mountain, TN


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: Unexpected motion can result from a patient’s sneeze, cough, tremble, deep breath or any possible movement related to uncomfortable set up/long treatment time. These movements can cause target position motion, thus decrease the accuracy of the treatment. In the present work, a simple patient surface monitoring method is described to control the radiation beam on/off when an unexpected movement occurs during the treatment.

Methods: This study is focused on non-gated treatments where the respiratory motion is not typically tracked for treatment accuracy. The Varian RPM system was used to control the beam on/off. A reflective marker was placed on the patient’s surface close to treatment site. Amplitude gating mode was used and the gating thresholds were established to include the patient’s respiratory motion, i.e. the patient’s normal breathing motion was ignored. When unexpected motion occurred, the tracking system interrupted the beam immediately to avoid dose delivery to an unplanned location. When patient motion becomes regular, the treatment was restarted automatically.

Results: A volunteer lay on the treatment couch and simulated four different phenomenon including cough, tremble, deep breath, and movement related to uncomfortable set up. Thorax, abdomen, and pelvis treatment sites were tested by placing the reflective marker at each site. The active tracking method was able to catch all four actions in a thorax treatment. For abdomen treatment and pelvis treatment, this method detected cough, deep breath, and uncomfortable movement.

Conclusion: This simple technique may improve accuracy in treatment delivery without extra treatment planning, and minimal additions to setup. If no movement occurred, the treatment time remained the same compared with unmonitored free breathing treatments. If an unexpected motion occurs, this method reduced the possibility of unintended treatment delivery and uncertainty in localization.


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