Motion Tracking for Respiratory Motion in Radiosurgery

Achim Schweikard, John R. Adler, Jr.


Respiratory motion is difticult to track with conventional radiotherapy ayhtems. To track a moving target, the beam source or the patient would have to be moved in real-time during treatment. Safety margins currently used in radiation therapy increase the radiation dose by a very large amount. An accurate tracking method for following the motion of the tumor is of utmost clinical relevance. We investigate methods to compensate for respiratory motion using robotic radiosurgery with a modified Cyberknife system. Thus. the therapeutic beam is moved by a robotic arm. and follows the moving target tumor. To determine the precise position of the moving target we combine infrared trackin g with synchronized X-ray imaging. Infrared emitters are used to record the motion of the patient’s skin surface. The position of internal gold fiducials is computed repeatedly during treatment. via computer image processing. Thus, stereo X-ray imaging is used during treatment to determine the precise spatial location of the implanted gold markers via automated image analysis. Using stereo X-ray imaging, precise marker positions can be established once every IO seconds. External markers (placed on the patient’s skin) can be tracked automatically with optical methods at very high speed. Updated positions can be reported to the control computer more than 60 times per second. External markers alone cannot adequately reflect internal displacements caused by breathing motion. Large external motion may occur together with very small internal motion. and vice versa. In addition the direction of the visible external motion may deviate substantially from the direction of the target motion. We correlate the motion between external and internal markers. to predict the placement of the internal target in time periods between X-ray imaging. Although the infrared tracking is combined with X-ray imaging, it is not necessary to detect to position of the infrared emitters in an X-ray image. Time-stamps permit the simultaneous positions of both marker types to be established. and can therefore be used to determine respiratory motion patterns. These motion patterns are patient-specific, and can be updated durin g treatment. Experiments show that robotic tracking is ?dst and reliable enough to track the moving internal target. Clinical trials confirm our hypothesis that internal motion and external motion can indeed be correlated to predict internal motion with very high accuracy and reliability.
Original languageEnglish
Number of pages1
Publication statusPublished - 01.10.2000
EventProceedings of the 42nd annual ASTRO meeting - Boston, United States
Duration: 22.10.200025.10.2000


ConferenceProceedings of the 42nd annual ASTRO meeting
Abbreviated titleASTRO 2000
Country/TerritoryUnited States
Internet address


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