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Sunday, January 27, 2019

ANPA monthly talk series: January

Potential Efficacy of the Monte Carlo Dose Calculations of 6MV Flattening Filter-Free Photon Beam of M6 Cyberknife® System

Taindra Neupane, Theodora Leventouri, and Charles Shang
Department of Physics (Medical Physics) Forida Atlantic University, Florida, USA

The retrospective MapCheck measurements for 50 patient’s treatment plans suggested that the MapCheck could be effectively employed in routine patient specific quality assurance in M6 Cyberknife with beams delivered at different treatment angles. However, it suggested that for highly intensity modulated MLC plans, small segments of width < 8 mm should further be analyzed with a modified (-4%) correction factor. The preliminary results of the MC simulations of M6 Cyberknife using the EGSnrc program for 2-5 millions of incident particles histories in BEAMnrc and 10-20 millions in DOSXYZnrc have shown dose uncertainties within 3% for all the open fields (7.6 x 7.7 mm2 to 100 x 100 mm2). The energy and FWHM of incident particle source were optimized by comparing with water phantom measurements and the optimized energy, E = 7 MeV and FWHM = 2.2 mm were found. Good agreements for the field size (within 2%) and the dose outputs (within 3%) were found between the MC simulations and measurements in water phantom at 800 mm SAD for all the open fields. This research can further be extended to small MLC segments to investigate the field specific and detector specific correction factors using Gamma analysis and adapting the parallel computing in future.
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Graphene as a high-throughput platform to measure the charge dynamics at organic semiconducting interfaces

Bhupal Kattel, Tika R. Kafle, Liang Qin, and Wai-Lun Chan

Department of Physics, University of Kansas, Lawrence, KS 66045, USA


The formation of charge transfer (CT) excitons at the interface of organic semiconductors hinders the charge generation efficiency in devices such as photovoltaics and photodetectors. Therefore, a complete picture of how the tightly-bound CT excitons dissociate into free carriers is essential to improve the performance of these devices. The overall charge extraction mechanism can involve multiple stages such as charge transfer and charge separation. In this talk, I will present our newly developed time-resolved photoelectrical technique to measure the dynamics of charge-separation at a prototype organic donor-acceptor interface: Zinc phthalocyanine/fullerene (ZnPc/C60) interface. This method utilizes graphene as the electrical sensor to measure the ultrafast dissociation dynamics of CT excitons. By controlling the thickness of sample, we selectively measure the dissociation of the delocalized and localized CT states. We observe two distinct channels of dissociation- athermal dissociation of the hot-delocalized CT states and the thermally-activated dissociation of the localized CT states. The former channel is found to have faster dissociation rate and yield ~3 times higher than the latter. I will also shortly present the use of this technique in other materials such as hybrid perovskite-PCBM interfaces, in order to demonstrate the versatility of our method.

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Please join us by WebEx on Sunday, January 27, 2019 @ 9:30 PM EST.

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