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Remote Dosimetric IMRT Auditing Using EPID Derived Doses in Patient CT Model and DVH Analysis

P Greer

P Greer1,3*, R David2,3 , (1) Calvary Mater Newcastle, Newcastle, Australia, (2) CCLHD, Gosford, NSW, Australia, (3) University of Newcastle, Newcastle, Australia


SU-I-GPD-T-255 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To investigate the feasibility of a new method to perform remote dosimetric IMRT audits for clinical trials using EPID reconstructed delivered doses in a patient CT model and DVH analysis.

Methods: The remote center developed a trial benchmarking IMRT plan in a reference patient CT dataset, calculated dose for each beam in a flat virtual water phantom, and acquired an integrated image of each beam with EPID in-air. The auditing central site converted EPID image to dose in flat virtual water phantom, estimated delivered dose in the reference patient CT dataset and performed DVH analysis comparing to the benchmarking plan. The sensitivity of the method to deliberately introduced dose errors was compared to traditional gamma comparison. The percentage change in DVH parameters (2% acceptance criterion) was compared to 2D gamma for flat-phantom planar dose with 2%,2mm criteria (90% pass-rate acceptance criterion). The method was trialled as a remote audit procedure for 3 centers to determine feasibility. The centers planned a benchmark post-prostatectomy trial plan for the audit.

Results: For introduced dose errors ranging from ±1% to ±5% for 6 IMRT fields the gamma comparison was sensitive to 28% of the introduced errors whereas the DVH analysis was sensitive to 71% of the errors. The remote audit results were assessed by comparing D2, D98 for the PTV and V60 for the rectum. The difference between PTV dose for the EPID reconstruction compared to the reference plan was on average 1.1% (SD 0.6%). The difference between the rectal dose metric was on average 1.5% (SD 1.0%).

Conclusion: The new method is more sensitive to dose delivery errors than gamma comparison. The method is feasible to perform remotely for dosimetric audits and is potentially less expensive, more rapid to perform, and results in more clinically meaningful results than current audit methods.

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