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Evaluation of SRSMapCHECK for Small-Field CyberKnife G4 Patient Specific Quality Control

B Wilson*, J Szanto, The Ottawa Hospital, Ottawa, ON CA,


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: The SRSMapCHECK (Sun Nuclear Corporation), is a diode array dosimeter developed with the intent of replacing film-based small field patient specific dosimetry. In this work, we evaluate the dosimetric and geometric accuracy of the device. We also measured its functionality and usability for measuring patient specific and machine specific QC of CyberKnife treatments.

Methods: The device was placed in the accompanying bullet shaped phantom and the angular dependence was measured. Dose rate, and field size were measured for cones ranging from 5-60mm. We tested the functionality of the device for patient specific QC by measuring an array of CyberKnife G4 treatment sites including prostate, spine, brain metastases, AVM, trigeminal neuralgia and liver.

Results: We measured an angular dependence on detector response of 2% in the roll direction and 1.5% error in the yaw direction. We measured up to 4% variation in relative output factor measurements when compared with the treatment planning calculated values. There was a 1% dose rate dependence measured between 70-2200 MU/min with a 10MV FFF beam. All patient specific QC passed with greater than 99% gamma pass rate at 2% 1mm passing criteria. The smallest cone treatment (5 mm trigeminal neuralgia), passed with 0.2% central axis dose error and (0.2mm, 0.2mm, 0 mm) calculated shift which demonstrates very accurate tolerances of the device. The device was also found to be suitable for the measurement of 60 mm profiles.

Conclusion: The SRSMapCHECK was shown to be suitable for all patient-specific measurements in the treatments that were tested. Further clinical experience is required to determine whether the dosimetric errors introduced by dose rate, angular response and field size necessitate a 2% or 3%, 1 mm passing criteria.


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