2016 AAPM Annual Meeting
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Session Title: The EPID Strikes Back
Question 1: Using the EPID for in-treatment target position assessment has the benefit that:
Reference:Rottmann et al 2010, Phys Med Biol Vol. 55(18), pp. 5585-5598 http://dx.doi.org/10.1088/0031-9155/58/12/4195
Choice A:The BEV perspective captures both directions of steep dose gradient.
Choice B:MV image contrast formation is dominated by the photoelectric effect.
Choice C:The additional patient dose is negligible if the EPID is placed >15cm away from the patient.
Choice D:A and C
Choice E:None of the above
Question 2: What are the requirements to generate in-treatment fluoroscopic 3D images from in-treatment fluoroscopic (2D) EPID images?
Reference:Mishra et al 2014, Med. Phys. 41, 081713 http://dx.doi.org/10.1118/1.4889779
Choice A:The gantry has to rotate for a minimum of 180° during treatment delivery.
Choice B:A patient specific motion model derived from pre-treatment imaging (4DCT).
Choice C:Optimization of motion model parameters to generate the DRR best matching the current EPID image.
Choice D:B and C
Choice E:None of the above
Question 3: Transit dose is measured through different phantom thicknesses with an EPID. To determine the dose that would be measured by an ion-chamber in solid water at the same position, a non-linear mapping from EPID signal to dose is required. Assuming that this is only due to primary dose i.e. ignoring scatter, what is the main physical mechanism for the difference in EPID response to ion-chamber?
Reference:Chen et al. Med. Phys 33(3), 584-594, 2006
Choice A:Attenuation of the beam
Choice B:Settings of the EPID acquisition
Choice C:Energy-dependent response of the EPID
Choice D:Different size of the EPID
Question 4: The major difference for an EPID backprojection method for VMAT compared to IMRT is:
Reference:Mans et al. Radiother. Oncol. 94, 181-187, 2010
Choice A:Dose calculation method
Choice B:Requirement for cine-mode imaging
Choice C:Increase in EPID sensitivity
Choice D:EPID sag/flex correction
Question 5: What is the typical Detective Quantum Efficiency of current flat-panel electronic portal imaging devices?
Reference:Antonuk LE: Electronic Portal Imaging Devices: A Review and Historical Perspective of Contemporary Technologies and Research.  Phys. Med. Biol. 47(6), R31-R65, 2002.  PMID: 11936185
Choice A:1-2%
Choice B:30-35%
Choice C:60-70%
Choice D:80-100%
Question 6: It is possible to significantly improve the Detective Quantum Efficiency of flat-panel electronic portal imaging devices while largely preserving spatial resolution.
Reference:Wang Y, Antonuk LE, Zhao Q, El-Mohri Y and Perma L:  High-DQE EPIDs based on thick, segmented BGO and CsI:Tl scintillators:  Performance evaluation at extremely low doses.  Med. Phys. 36(12), 5707-5718, 2009.  PMID: 20095283  PMCID: PMC2797046
Choice A:True.
Choice B:False.
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