We also found that 10-MV FFF showed very similar trend. The agreement ranged from 0.996 to 1.004 and 0.995 to 1.002 for 6-MV and 6-MV FFF, respectively. The NPSF agreement between the 6-MV and 6-MV FFF with the BJR#25 were all within ☐.5%. From BJR #25, NPSFs were obtained for comparison with the measurements. For in-air measurements, the chamber was positioned at 100 cm source-to-axis distance with appropriate build-up cap. For measurements in water, the chamber was positioned at 100 cm source-to-axis distance at the depth of dose maximum. Both water and in-air measurements were made to obtain NPSFs normalized to the 10 × 10 cm 2 field size. For all measurements, a Scanditronix CC04 ionization chamber was used. The purpose of this work was to determine whether the energy independent NPSFs BJR#25 are valid for comparison with FFF photon beams.Īll measurements were performed using a Varian TrueBeam linear accelerator with photon energies of 6-MV, 6-MV FFF and 10-MV FFF modes. During the commissioning of an accelerator with flattening filter free (FFF) photon beams (Varian True Beam 6 MV FFF and 10 MV FFF) we compared measured Phantom Scatter Factors (Sp) with the Normalized Peak Scatter Factors (NPSFs) from the British Journal of Radiology Supplement 25 (BJR #25). In the process of measuring and validating fundamental dosimetry data prior to the clinical use of a treatment unit, it is prudent to compare measurements with previously published equivalent data.
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