Purpose: To evaluate variability in response between two copies of SunNuclear’s SRS MapCHECK diode array.
Methods: Measurements suitable for device commissioning were collected with each copy of the SRS MapCHECK. The irradiations tested the devices’ dependencies on beam angle, pulse repetition rate (PRR), dose per pulse (DPP), total dose, and field size for flattened and unflattened 6MV and 10MV beams. Angular dependence was tested with both axial and vertex beams. DPP was varied by changing SDD. Additionally, three treatment plans (lung SBRT, spine SBRT, 3D conformal SRS) for each energy were delivered to each device. Measurements were collected on one Varian TrueBeam on the same day to reduce variability of linac behavior. Differences in dependence on each variable were compared between the two devices.
Results: Differences in dependence on beam angle were less than 1% for angles >10° from parallel with the array for axial and vertex orientations. Changing PRR and DPP resulted in differences between devices of less than 0.5% across the available range of PRR, less than 0.8% across the range of DPP, and within 0.4% for all but the highest DPP. Dose linearity varied by <0.2% between the two devices from 10 to 3500 cGy. Variability in field size dependence was <0.5% for all field sizes except for the 10FFF 1cmx1cm field, where the greatest difference was 0.9%. Finally, passing rates from each device were at least 94.8% and within 3% of each other using a 1%/1mm gamma comparison (lung SBRT and 3D SRS, all energies) and >89% and within 4.3% of each other with 2%/2mm criteria for the spine SBRT plans.
Conclusion: The two diode arrays responded similarly across a wide range of tests. Only small differences in dependence to various conditions were observed. Gamma passing rates matched closely with more stringent criteria than used clinically.