Program Information
Remote Dosmetric Auditing of VMAT Deliveries for Clinical Trials Using EPID
K Legge1*, J Lehmann2 , P Vial3 , N Miri1 , P Greer1,2 , (1) University of Newcastle, Australia (2) Calvary Mater Newcastle, Australia (3) Liverpool Hospital, Australia.
Presentations
SU-D-201-6 (Sunday, July 31, 2016) 2:05 PM - 3:00 PM Room: 201
Purpose:To develop a method for remote dosimetric auditing the delivery of VMAT using EPID which allows for simple, inexpensive and time efficient dosimetric credentialing for clinical trials.
Methods:Remote centers are provided with CT datasets and planning guidelines to produce VMAT plans for a head and neck and a post-prostatectomy treatment. Plans are transferred in the planning system to two virtual water equivalent phantoms, one flat and one cylindrical. Cine images are acquired during VMAT delivery to the EPID in air with gantry angle recorded in image headers. Centers also deliver provided calibration plans to enable EPID signal to dose conversion, determination of the central axis, and correction of EPID sag prior to analysis. EPID images and planned doses are sent to the central site. EPID cine images are converted to dose in the virtual phantoms using an established backprojection method (King et al., Med.Phys. 2012) with EPID backscatter correction. Individual arcs (with gantry angles collapsed to zero) are evaluated at 10 cm depth in the flat phantom using 2D gamma, and total doses are evaluated in the cylindrical phantom using 3D gamma. Results are reported for criteria of 3%,3mm, 3%,2mm and 2%,2mm for all points greater than 10% of global maximum.
Results:The pilot study for Varian centers has commenced, and three centers have been audited for head and neck plans and two for post-prostatectomy plans to date. The mean pass rate for arc-by-arc 2D analysis at 3%,3mm is 99.5% and for 3D analysis is 95.8%. A method for Elekta linacs using an inclinometer for gantry angle information is under development.
Conclusion:Preliminary results for this new method are promising. The method takes advantage of EPID equipment available at most centers and clinically established software to provide a feasible, low cost solution to credentialing centers for clinical trials.
Funding Support, Disclosures, and Conflict of Interest: Funding has been provided from Calvary Mater Newcastle Department of Radiation Oncology, TROG Cancer Research and the University of Newcastle. Kimberley Legge is the recipient of an Australian Postgraduate Award. Narges Miri is a recipient of a University of Newcastle postgraduate scholarship.
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