(Saturday, 3/30/2019)
Room: Exhibit Hall
Purpose: This study is aiming to evaluate a 2D detector array (SRS MapCHECK [SMC] from Sun Nuclear Corp.) for SRS plan verification.
Methods: The SMC was placed in a StereoPHAN phantom and irradiated with a conventional 6MV or a 6MVFFF beam from a Varian TrueBeam accelerator. A comprehensive suite of evaluation measurements was performed, among them the 180° rotation, angular dependence (against an ion chamber, IC), field size dependence (against a scintillator), and end-to-end (against radiochromic film) tests.
Results: The mean differences in the flip test detector readings were within 0.01±0.2%. The SMC sensitivity angular dependence in the axial plane, with both energies, was under 2% for all gantry angles, except with the beam central axis within ±5° from the array plane. Most combinations of gantry and couch angles resulted in <2% deviation from the IC. Discrepancies of 2-3% were observed with the beams incident at ±30° to the detector array and the couch rotations >50°. The output factors agreed with the scintillator within 2%, with the only exception of the 6X 5mm field (3.2% error). For the SRS plans, the average γ-analysis passing rates were 98.03% ± 0.8% and 97.95% ± 1.2% for 3%/1mm and 2%/2mm criteria, respectively.
Conclusion: SRS MapCHECK detector spacing (2.5 mm) makes it theoretically capable of faithfully representing any gradients encountered in modern x-ray radiotherapy. Our data show that after application of built-in correction factors, its calibration is sufficiently accurate to make it a feasible device for the composite SRS measurements, provided that the couch/gantry angle combinations do not result in direct irradiation of the device electronics. SMC exhibits common sensitivity variations when the beam is nearly parallel to the detector plane, which does not meaningfully affect the composite dose.
Funding Support, Disclosures, and Conflict of Interest: This work was supported in part by a grant from Sun Nuclear Corporation. SA is a graduate student supported by SNC grant, VF is the PI on the project.
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