(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To evaluate the suitability of the SRS MapCHECK for patient-specific quality assurance (PSQA) of CyberKnife M6 plans in comparison to ionization chamber and radiochromic film.
Methods: PSQA plans for the most recent eleven CyberKnife patients at our center were generated for the SRS MapCHECK device in the StereoPHAN phantom. The device had a CyberKnife-specific dose calibration and an array calibration generated using a 6 MV FFF beam from a Varian TrueBeam linear accelerator. Treatment sites for the patient plans included brain, lung, spine, and liver. All PSQA plans were calculated using the Monte Carlo algorithm at high resolution and an uncertainty of 1.0%. Four fiducial markers inside the SRS MapCHECK device were used to position the device along with the StereoPHAN phantom. A 6DOF couch was used to correct for setup errors, and any residual corrections were taken into account during the treatment by the CyberKnife delivery system. The results were compared to standard PSQA using an Exradin A26 ionization chamber and radiochromic film. Gamma analysis for the SRS MapCHECK and radiochromic film measurements was performed at the 2%/2 mm threshold.
Results: Seven out of the eleven PSQA plans measured with the SRS MapCHECK had gamma pass rates exceeding 99.7%, with a median pass rate of 99.9%. Calculated shifts to maximize the pass rates were 1.0 mm or less in the lateral and longitudinal directions, and were applied in all cases. The median gamma pass rate for the radiochromic film measurements was 96.3%. One of the PSQA plans on the SRS MapCHECK had a pass rate below 80%, and the results were reproducible with a repeated delivery.
Conclusion: Although not yet officially supported by Sun Nuclear, the SRS MapCHECK shows promise as a replacement for radiochromic film and ionization chamber for CyberKnife PSQA, but some failures require further investigation.
Funding Support, Disclosures, and Conflict of Interest: Lena Tirpak is an employee of Sun Nuclear Corporation.
Keywords
Diodes, Quality Assurance, Stereotactic Radiosurgery
Taxonomy
TH- Radiation dose measurement devices: Multi-dimensional diode/chamber arrays
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