Point Dosimetry in Patient-specific Quality Assurance of a Robotic Radiosurgery System Using a Scintillation Detector.

PURPOSE: Patient-specific quality assurance (QA) for CyberKnife is typically performed using micro ionization chambers and film dosimetry. However, micro ionization chambers tend to underestimate dose measurements in small radiation fields. Therefore, scintillation detectors, with their small detector size, may be more suitable for point dosimetry in CyberKnife QA. The purpose of this study was to evaluate the utility of a scintillation detector (Exradin W2 [W2]) for point dose measurements in CyberKnife patient-specific QA.

METHODS: Dosimetric measurements for 50 treatment plans involving intracranial stereotactic radiotherapy were performed using both the W2 and a micro ionization chamber (Exradin A16 [A16]).

RESULTS: The mean point dose differences in patient-specific QA were 0.5% for W2 and -6.6% for A16; dose differences with W2 were generally within ±3%. Factors contributing to measurement robustness included the optical fiber dose for W2, and the static cable dose and collimator size for A16.