Room: Exhibit Hall | Forum 4
Purpose: The purpose of this study is to investigate the characteristics of a two dimensional (2D) diode detector array used with a stereotactic phantom (StereoPHAN) for use in the verification of stereotactic radiotherapy plans with field sizes up to 7x7 cm using 6X and 6FFF energy fields.
Methods: The SRS MapCHECK diode detector inserted in the StereoPHAN phantom, both from Sun Nuclear Corporation, was used on this study. The SRS MapCHECK is a 2D array of 1,013 diode detector on a 2.47 mm detector grip with a 0.5mm resolution. The detector reproducibility, dose linearity, and angular dependence were investigated on the Varian TrueBeam STX unit for both 6X and 6FFF energies. Open and wedged field planar doses were also measured and compared with the predicted dose from the Varian Eclipse planning system.
Results: Reproducibility results in Figure 1 show a mean standard deviation was 0.20% and 0.43% for 6X and 6FFF beam, respectively, over the 46-day measurement period. Angular dependence results show that the largest central axis normalized dose response of 3.2% and 4.6%, for 6X and 6FFF, respectively, comes from side (perpendicular to the front). The linear response with dose for both 6X and 6FFF is shown in Figure 3. Table 1 shows excellent agreement between measured doses and calculated doses for static fields. Preliminary measurements for stereotactic VMAT plans in relative mode show excellent agreement with predicted dose using a 2%, 2mm gamma index.
Conclusion: The SRS MapCHECK-StereoPHAN detector system was investigated for use in pre-treatment verification of stereotactic plans. The SRS MapCHECK-StereoPHAN exhibited a reproducible and linear response to dose. There seems to be an angular dependence behavior that peaks at directions parallel to the detector axis. Initial planar dose comparisons show promise in the detectorâ€™s ability for use in routine stereotactic pre-treatment QA plans.