Program Information
QA BeamChecker Plus for the Daily Quality Assurance of a CyberKnife
J Gersh*, Gibbs Cancer Center & Research Institute - Pelham, Greer, SC
Presentations
PO-BPC-Exhibit Hall-16 (Saturday, March 7, 2015) Room: Exhibit Hall
PURPOSE:
Described is the utilization of the QA BeamChecker Plus (BC+, Standard Imaging Inc., Middleton, WI), for the efficient and consistent test of the CyberKnife’s (CK) output constancy.
METHODS:
To use the BC+ with the CK, a water-equivalent extension is attached to the BC+. This contains four fiducial markers on the same coronal plane; appearing with acceptable separation on the CK’s stereoscopic imagers. The user first attaches the CK extension to the BC+ and CT scan the phantom in a technique consistent with the density table setup in the treatment planning system. Following export of the imaging study and import into the MultiPlan TPS, five targets are contoured in the coronal plane (center, superior, left, inferior, and right), each representing the central and peripheral-most plane-parallel ionization detectors of the BC+ unit. During planning, single-path isocentric targets are placed on each of the five detectors. For each of the targets, 500 MU are delivered. Baselines are acquired and automatically corrected for temperature and pressure.
RESULTS:
Testing uncertainty in repeat measurements, ten measurements were performed immediately after setting baselines. Average output was +0.25% with an SD of 0.11%. On the same day as baseline acquisition, ten acquisitions were delivered with a change in the position of the BC+ system. This required the treatment localization system to recalculate translation and rotation as well as the positional adjustment of the treatment nodes of the accelerator. By performing this study on the same day as the baseline acquisition, output variation is suppressed. The average output was +0.30% high with an SD of 0.13%. In a three-week study, average output was +0.23% with an SD of 0.12%.
CONCLUSION:
When used in conjunction with the CK-specific extension, the QA BeamChecker Plus provides the user with an efficient and consistent means for the daily verification of beam output.
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