Browsing by Author "Chen, Z."

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Analysis of delivery and recalculation of dose using DICOM treatment records
    (Elsevier, 2022) Chen, Z.; Moyers, M.F.; Deng, Y.; Chen, H.L.; Li, J.; Shen, Z.M.; Lin, J.; Wang, Q.; Yepes, P.
    Objective A procedure has been proposed for patient-specific QA that, instead of comparing a measurement to the planned dose, compares the dose calculated by an independent system to the dose calculated by the planning system. It is still prudent, however, to check the accuracy of the beam delivery. For this purpose, the DICOM records from the first treatment fraction can be compared to the planned treatment using an in-house developed planning system. Methods Totally 1,398 patient portals were subjected to the new QA procedure. The dose distribution for each portal was first recalculated on a water phantom by two treatment planning systems and the dose distributions were compared. When agreement was observed, the patient was allowed to start treatment without a measurement. The record from the first day was imported into an in-house planning system which was used to evaluate the delivery for errors and calculate the delivered dose distribution and compare it to the planned dose distribution. Results A total of 266 portals passed a strict comparison between the clinical and QA dose calculations and directly used for treatment without measurements. For those portals, the comparison of the delivery records to the plan showed that 99% of spot positions deviated less than 0.2 ​mm and 99.7% of spot metersets deviated by less than 0.3%. On the other hand, 64 portals showed spot size deviations greater than the tolerance of ± 15% with some as large as ±25%. For 32 portals in which the record was used to calculate the delivered dose distribution, the Gamma passing rates between the planned and delivered distributions were always above 95% using a 2% dose difference and 2 ​mm distance-to-agreement criteria. Conclusions The new QA process has been implemented slowly with strict constraints. The amount of beam time required has been reduced while maintaining safety.
  • Thumbnail Image
    Item
    Combined Measurement of the Higgs Boson Mass in pp Collisions at √s=7 and 8 TeV with the ATLAS and CMS Experiments
    (American Physical Society, 2015) Adair, A.; Akgun, B.; Chen, Z.; Ecklund, K.M.; Geurts, F.J.M.; Guilbaud, M.; Li, W.; Michlin, B.; Northup, M.; Padley, B.P.; Redjimi, R.; Roberts, J.; Rorie, J.; Tu, Z.; Zabel, J.
    A measurement of the Higgs boson mass is presented based on the combined data samples of the ATLAS and CMS experiments at the CERN LHC in the H→γγ and H→ZZ→4ℓ decay channels. The results are obtained from a simultaneous fit to the reconstructed invariant mass peaks in the two channels and for the two experiments. The measured masses from the individual channels and the two experiments are found to be consistent among themselves. The combined measured mass of the Higgs boson is mH=125.09±0.21 (stat)±0.11 (syst)  GeV.
  • Thumbnail Image
    Item
    Role of internal motions and molecular geometry on the NMR relaxation of hydrocarbons
    (AIP, 2018) Singer, P.M.; Asthagiri, D.; Chen, Z.; Parambathu, A. Valiya; Hirasaki, G.J.; Chapman, W.G.
    The role of internal motions and molecular geometry on 1H NMR relaxation rates in liquid-state hydrocarbons is investigated using MD (molecular dynamics) simulations of the autocorrelation functions for intramolecular and intermolecular 1H–1H dipole-dipole interactions. The effects of molecular geometry and internal motions on the functional form of the autocorrelation functions are studied by comparing symmetric molecules such as neopentane and benzene to corresponding straight-chain alkanes n-pentane and n-hexane, respectively. Comparison of rigid versus flexible molecules shows that internal motions cause the intramolecular and intermolecular correlation-times to get significantly shorter, and the corresponding relaxation rates to get significantly smaller, especially for longer-chain n-alkanes. Site-by-site simulations of 1H’s across the chains indicate significant variations in correlation times and relaxation rates across the molecule, and comparison with measurements reveals insights into cross-relaxation effects. Furthermore, the simulations reveal new insights into the relative strength of intramolecular versus intermolecular relaxation as a function of internal motions, as a function of molecular geometry, and on a site-by-site basis across the chain.