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Effect of Scanning Speed On MV and FFF Dosimetric Measurements Using a Scanning Chamber and EDGE Detector


E Sayler

E Sayler*, S Gardner, I Buzurovic, M Studenski, Thomas Jefferson University, Philadelphia, PA

SU-E-T-131 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:

This study quantifies the effect of scanning speed on photon beam profiles and PDD measurements in a water tank.

Methods:

Data was acquired using OmniPro-Accept 7 (IBA Dosimetry) for Varian TruebeamTM, 6 MV and 6 FFF, 3x3 and 10x10 cm² fields. A CC13 compact chamber (Wellhofer) and an EDGE Detector (Sun Nuclear) were used to measure PDD, inline and crossline profiles (at dmax and 10 cm depths) in a Blue Phantom² (IBA Dosimetry). Each scan was acquired five times at ten different scanning speeds [0.35 - 2.50 cm/sec], and compared to a reference scan (discrete steps of 1.0 mm/step, 2 sec/step). MATLAB was used to calculate the mean difference between the reference and scanned data, and the standard deviation, at each measured point in the scan.

Results:

For the CC13, the mean difference and the standard deviation of the measured PDDs increased with increasing scan speed for all field sizes and energies. The range of mean differences for speeds below 1.0 cm/sec was [0.04% - 0.13%], and above 1.5 cm/sec was [0.13% - 0.30%].

For the EDGE detector, the mean difference and the standard deviation of the PDDs also increased with increasing scan speed. The range of mean differences for speeds below 1.0 cm/sec was [0.09% - 0.28%], and above 1.5 cm/sec was [0.21% - 0.57%].

The mean difference for in-field profile scans did not show significant dependence on scanning speed for either detector. The range of mean differences was [0.08% - 0.99%] for the CC13, and [0.13% - 2.16%] for the EDGE.

Conclusion:

Increased scanning speed was correlated with an increase in the mean difference of PDD curves. The mean difference for in-field profile scans did not show significant dependence on scanning speed for either detector. The EDGE scan data exhibited larger mean difference for all scan types.

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