ESTRO 2021 Abstract Book

S233

ESTRO 2021

For the same detector, the differences observed between RFM and IFM were <0,5%, except for the diode at 6 FFF energy (1,4%). The correction factors applied tend to homogenize the results measured with the different detectors, finding discrepancies <1% in most cases, although they are occasionally exceeded: 2,3% for 2x2 cm 2 6 FFF measured with diode, 3% for 1x1 cm 2 6 WFF measured with EBT3, and 2,1% for 1x1 cm 2 10 WFF measured with Pinpoint. EBT3 data shows good agreement with other detectors, except for 10 WFF energy (>5%). On the other hand, the use of the DC method (without applying TRS-483 correction factors) implies discrepancies >2% for the smallest fields: -4% for 1x1 cm 2 measured with Pinpoint, and up to 5% for 0,6x0,6 cm 2 with diode. Conclusion The correction factors published in the TRS-483 protocol make it possible to homogenize the OF data and reduce the discrepancies between the measurements made with different detectors, obtaining differences between both methods lower than 1%. On the other hand, the DC method (IFM without correction) can lead to underestimations or overestimations about 4% in OF values for field sizes < 1x1cm 2 , therefore its use in this range is not recommended. PH-0323 clinical evaluation of the myQA SRS detector for stereotactic body radiotherapy plan verification C. Stepanek 1 , A. Stapleton 1 , J. Haynes 1 , S. Fletcher 1 1 University Hospitals Bristol & Weston NHS Foundation Trust, Radiotherapy Physics, Bristol, United Kingdom Purpose or Objective We report the clinical testing of the myQA SRS detector (IBA Dosimetry, Germany), a unique sensor based on Complementary Metal-Oxide-Semiconductor (CMOS) technology designed for stereotactic plan verification, and machine QA. It offers sub-mm spatial resolution & aims to provide good sensitivity & specificity to treatment delivery errors.