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Implementation of the Electronic Portal Imaging Device for Daily CyberKnife Quality Assurance

L Wang*, A Lo , A Ho , Stanford University Cancer Center, Stanford, CA


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

Room: Exhibit Hall

Purpose: The CyberKnife M6 is equipped with variable aperture Iris collimator and InCise 2 Multi-Leaf Collimator (MLC). The daily targeting accuracy and collimator quality assurance (QA) are traditionally performed with films which are time consuming without instantaneous results. To improve the efficiency and stability, a filmless QA system using the newly released StereoChecker (Standard Imaging Inc., Middleton, WI) was implemented in our institute for CyberKnife M6 system. This work reports our eight-month experience and QA results using the StereoChecker.

Methods: The StereoChecker consists of a high spatial-resolution (0.2mm) electronic portal imaging device (EPID) packed in a case with imbedded fiducial markers. CT images of the device were provided by the vendor. Three treatment plans were created following the instructions: 1) Target Localization System (TLS) plan is a five-field iso-centric plan for targeting accuracy QA. 2) Iris QA plan delivers one anterior beam at all the available apertures. 3) MLC QA plan delivers a five-strip garden fence pattern using all the leaf pairs. The base lines were first setup by the physicist. Daily QA was performed by the therapists in the morning. The results were compared with the baseline, saved and reviewed by the physicists.

Results: The QA procedure with all three plans takes about 40 minutes including the time used for equipment setup and collimator exchanges. The targeting deviation from the TLS QA are: -0.035mm±0.171mm Right/Left, 0.074mm±0.238mm Superior/Inferior, 0.056mm±0.124mm Anterior/Posterior, and 0.310mm±0.097mm Total. For 11 Iris field sizes (7.5mm-60mm) measured, average field width deviation from the baseline is -0.05mm ±0.03mm, with a maximum deviation < 0.2mm. All the MLC garden fence measurements passed with 0.5mm leaf position deviation limit.

Conclusion: The StereoChecker is an accurate and stable filmless QA tool for CyberKnife. Better software design and integration with the delivery system could further improve the QA efficiency.


Quality Assurance, Flat-panel Imagers


TH- External beam- photons: cyberknife

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