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Purpose: This study aims to evaluate different methods for calibrating EBT-XD films to develop a precise pre-treatment verification method for stereotactic radiotherapy (SRT) patients using the HyperArc (HA, Varian Medical System) technique. Methods: Gafchromic EBT-XD films were calibrated using three different approaches: manual calibration, EDW calibration, and PDD calibration. Films were digitalized with an Epson V850 Pro scanner applying the local scanning protocol. Three clinical treatment plans were selected for evaluation. Patient-specific QA films were irradiated in the Mobius MVP phantom and the STEEV phantom. Scanned film images were converted into dose images using the calibration curves. Gamma analysis was performed to compare film dose and TPS calculated dose with various criteria. Results: The scan-to-scan variation was evaluated to be ≤ 0.2%. The accuracy of the calibration curves was verified and the deviation from the converted dose deviates ≤ 3% from the known delivered dose. The gamma passing rate for all calibration methods was found to be over 94% with clinically relevant criteria. EDW calibration demonstrated higher average gamma passing rates compared to the manual method for single target plans, which is 99% ± 1.2% and 98.8% ± 1.5%, respectively. PDD method demonstrated improved agreement for multiple targets with the result of 99.3% ± 0.8%. Conclusions: The three calibration methods were validated, and they produced accurate calibration curves for EBT-XD films to enable pre-treatment patient-specific QA for stereotactic radiotherapy. [ABSTRACT FROM AUTHOR]

Abstract: The inhibition of catalytic hydrodesulfurization (HDS) by basic nitrogen compounds is an important problem in the production of ultra low sulfur transportation fuels and the origin of the inhibition effects is presently elucidated by performing density functional theory (DFT) calculations on the interaction of pyridine with the two types of edges of MoS2 catalyst nanoparticles. Particular attention is given to studies of the hydrogenation (HYD) pathway in HDS since this is the favored pathway for refractory sulfur compounds and it is the pathway, which is most severely poisoned by basic nitrogen compounds. In order to understand the observed inhibitor trends, DFT studies on the adsorption of benzene, which is a weaker poison than pyridine, and H2S, which has no or only a very minor influence on the HYD pathway, have also been made. We find that the adsorption of pyridine is quite strong and especially strong at positions along the so-called Mo edge. Thus, the HYD reaction most likely involves sites at this edge. This suggestion is substantiated by the observation that the adsorption blocks the metallic like so-called brim sites, which were recently shown to be involved in the HYD pathway. Furthermore, H2S is observed not to interact strongly with these sites. The present results have also provided insight into the nitrogen compound inhibition of the direct desulfurization DDS pathway. The difference in the poisoning by benzene and pyridine is observed to be related to the ease with which hydrogen from neighboring SH group can be transferred to the pyridine molecule resulting in the creation of more strongly held pyridinium ions. At the so-called S edge, hydrogen is tightly bound and this transfer is not favored. The present results, therefore, also stress the importance of the hydrogen binding properties of HDS catalysts. [Copyright &y& Elsevier]