Related Experiment Video
Updated: Jul 13, 2026
Stereotactic Radiosurgery for Gynecologic Cancer
Published on: April 17, 2012
Radiation exposure during head repositioning with the automatic positioning system for gamma knife radiosurgery
Yoichi Watanabe1, Bruce J Gerbi
1Department of Therapeutic Radiology, University of Minnesota, 420 Delaware Street, Minneapolis, MN 55455, USA. watan016@umn.edu
Purpose:
To measure radiation exposure to a patient during head repositioning with the automatic positioning system (APS) for Gamma Knife radiosurgery.
Methods And Materials:
A 16-cm diameter spherical solid phantom, provided by the manufacturer, was mounted to the APS unit using a custom-made holder. A small-volume ionization chamber (0.07-cm(3) volume) was placed at the center of the phantom. We recorded the temporal variation of ionization current during the entire treatment. Measurements were made for 3 test cases and 7 clinical cases.
Results:
The average transit time between successive shots, during which the APS unit was moving the phantom for repositioning the shot coordinates, was 20.5 s for 9 cases. The average dose rate, which was measured at the center of the phantom and at a point outside the shot location, was 0.36 +/- 0.09 cGy/min when the beam output was approximately 3.03 Gy/min for the 18-mm collimator helmet. Hence, the additional intracranial radiation dose during the APS-driven head repositioning between two successive shots (or APS transit dose) was 0.12 +/- 0.050 cGy. The APS transit dose was independent of the helmet size and the position of shots within the phantom relative to the measurement point.
Conclusion:
The head repositioning with the APS system adds a small but not negligible dose to the dose expected for the manual repositioning method.
