(Saturday, 4/7/2018) 10:30 AM - 12:30 PM
Room: Marquis Ballroom 5-8
Purpose: Stereotactic Radiosurgery (SRS) and Body Radiotherapy (SBRT) commonly utilize small field sizes for radiation delivery, and thus require high spatial resolution quality assurance (QA) devices. Diodes offer high spatial resolution but are also known to exhibit dependencies on field size, beam energy, dose rate, and incident beam angle, reducing dose measurement accuracy. The purpose of this study is to evaluate the dosimetric accuracy of a high spatial resolution diode array.
Methods: A prototype of the SRSMC (SNC, Melbourne, FL) was used to evaluate and quantify its dependencies on field size (5mm to 80mm), beam energy (6MV WFF, 6MV FFF, and 10MV FFF), dose rate (repetition rates 100MU/min to 2400MU/min), and incident beam angle (0° to 90°). The SRSMC was calibrated on an Elekta VersaHD linac according to the vendor's instructions. Nine clinical VMAT treatment plans with energies of 6MV, 6MVFFF, and 10MVFFF were measured with the SRSMC, for which it was placed inside SNC’s StereoPHAN phantom and stereotactically positioned using the cone-beam CT on-board imaging system. The dose distribution was analyzed using the global gamma index with 3%/1mm criteria. The absolute dose was evaluated in comparison to the measured dose using a PinPoint3D (PTW, Freiburg, Germany) ion chamber in a separate plan delivery.
Results: The SRSMC has field size and beam energy dependencies for field sizes <2x2cm². Dose rate dependencies are >1% for dose rates <300 MU/min. Incident beam angle dependence is 2%. The end result of these dependencies on clinical plans is insignificant as measured by patient specific QA versus ion chamber dose.
Conclusion: The SRSMC is suitable for small field plan QA with some of the measured effects washing out on clinical plans. Plans with a majority of MUs delivered below 300MU/min and segment sizes <1x1cm² show larger errors and may require corrections of the diode dependencies.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by Sun Nuclear Corporation (SNC).
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