Commissioning of SRS Mapcheck for Cyberknife Mlc Patient-Specific QA
Abstract
Purpose
To commission the SRS MapCHECK detector for patient-specific quality assurance (PSQA) of CyberKnife multileaf collimator (MLC) treatment plans and to evaluate its clinical performance across multiple disease sites using stringent gamma analysis criteria.
Methods
An SRS MapCHECK detector (77 mm × 77 mm) mounted in the StereoPhan was scanned on a CT simulator with 1-mm slice thickness in two orientations (0° and 90°). The StereoPhan density was overridden to 1.20 g/cm³ in the Precision Treatment Planning System. A calibration plan was generated using the CyberKnife MLC with a 10 × 10 cm² field size and 100 MU delivered to the detector plane. The delivered dose, determined by averaging five points, was used to calibrate the SRS MapCHECK. Two patient QA templates were created from the 0° and 90° StereoPhan CT datasets. Embedded SRS MapCHECK fiducials were used for phantom setup and alignment. Templates were fused with approved patient plans to generate patient-specific QA plans. QA plans were registered to the phantom geometry and optimized by aligning the 50% isodose line within the active detector area. Manual phantom isocenter adjustments were performed to improve detector coverage, particularly for targets with large longitudinal extent. Patient-specific QA measurements were evaluated using gamma analysis with criteria of 3%/1 mm and a 10% dose threshold.
Results
The commissioned SRS MapCHECK system evaluated 113 CyberKnife MLC plans, including 27 spine, 42 prostate, 33 brain, 6 lung, and 5 abdominopelvic cases. All plans achieved gamma passing rates greater than 95% using the 3%/1 mm criteria. Dual StereoPhan orientations and manual registration improved detector coverage across a wide range of target sizes and anatomical sites.
Conclusion
SRS MapCHECK was successfully commissioned for CyberKnife MLC PSQA using stringent gamma criteria and demonstrated reliable performance across multiple treatment sites, supporting its clinical use for high-precision CyberKnife treatments.