arXiv subjects

Qianxia Wang

Publications and source records attributed to Qianxia Wang.

8 recordsLinked to original sources

arXiv2026

Beam modelling of Hitachi PROBEAT proton therapy system for a GPU-based Fast Monte Carlo dose engine

Background: An in-house dose engine independent of clinic TPS is not only a reliable tool for patient QA verification. More importantly, it plays vital role in cutting-edge research due to its flexibility in implementing new functions. In this study, we upgraded our existing beam model with using double-Gaussian distributions for both spatial and opening angle distributions of particles to obtain more accurate phase space files. It is expected to potentially improve the performance of this independent dose engine in both clinic and research at the expanded MD Anderson proton center.

physics.med-ph↗

arXiv2026

Planned, delivered and variable RBE dose difference analysis for a patient cohort with base-of-tongue cancer treated with IMPT

Background: To our knowledge, no tools have been installed in clinic for delivered and planned dose differences evaluation. This difference could be large for head and neck patients who suffer the most anatomy changes compared with other treatment sites due to long treatment courses and difficulty in eating. At the same time, variable RBE dose is an increasing concern for proton therapy. The constant RBE 1.1 is widely applied in clinics, however, the real RBE is larger than 1.1 especially at the end of beam range. How they are different and what the influence on plan evaluation are an interesting topic to investigate.

physics.med-ph↗

arXiv2025

Applying voxel-based analysis to oropharyngeal cancer proton therapy patients: a correlation study on radiation-induced acute dysphagia

Background: Voxel-based analysis (VBA) is an analytic approach to evaluate correlations between local dose and the development of different toxicities. DVHs are used for toxicity prediction as well. Compared with DVH, no contours are required for VBA technique and results tell specific voxels that may be related to the toxicity instead of the whole contoured area. The VBA has been used on different cancer sites and for different toxicities. Most of these studies included patients treated with photon, all published studies were based on planned dose and VBA tools used were developed in house. In our study, patient cohort were treated with proton, our VBA tool was developed based on RayStation and doses fed to the VBA tool were delivered doses with constant and two variable RBE models.

physics.med-ph↗

arXiv2021

Optimization of FLASH Proton Beams Using a Track-Repeating Algorithm

Methods: A phase space file in a plane at 202 mm downstream of the beam exit window is generated through tuning parameters to match FDC results with measured or MCNPX Monte Carlo-simulated integrated depth-dose distribution (IDD) and lateral dose profiles. To spread out the Bragg peak, widen the beam and reduce the penumbra, a ridge filter (RF), a high-Z material scatterer and a collimator with compensator are inserted in the beam path and their shapes and sizes have been optimized. The FDC calculations are validated by comparing Geant4 Monte Carlo simulations. In addition, a set of algorithms to automatically choose the optimum dimensions of the beam shaping elements is developed and tested using the same beams. At the last part, dose rates for optimized beams were estimated by scaling their dose distributions to that of their original beams. Results: The optimized 86.4 MeV beam had an 8.5 mm wide spread-out Bragg peak (SOBP) (proximal 90% to distal 90% of the maximum dose), 14.5 mm, 12.0 mm and 11.0 lateral widths with dose above 50%, 80% and 90% respectively and a 2.5 mm penumbra from 80% to 20% in the lateral profile for the energy. The 159.5 MeV beam had a SOBP of 39.0 mm and the lateral widths with dose above 50%, 80% and 90% of 20.5 mm, 15.0 and 12.5 mm when the source to surface distance (SSD) was 550 mm. Wider lateral widths was obtained with increased SSD. The FDC calculations had passing rates higher than 96% using 3mm/3% as the gamma-index criterion comparing with Geant4 simulations for both energies. The set of automatic algorithms can choose the proper dimensions for the high-density scatterer, RF, collimator and compensator efficiently. And the optimized 159.5 MeV beam with different SDDs had entrance dose rate higher than 40 Gy/s if the entrance dose rate of the original beam was 150 Gy/s.

physics.med-ph↗

arXiv2019

First evidence of enhanced recombination in astrophysical environments and the implications for plasma diagnostics

We report the first unambiguous observational evidence of Rydberg Enhanced Recombination (RER), a potentially important recombination mechanism that has hitherto been unexplored in low-temperature photoionized plasmas. RER shares similarities with dielectronic recombination, with the difference that the electron is captured into a highly excited state below the ionization threshold -- rather than above the threshold -- of the recombining ion. We predict transitions of carbon and oxygen ions that are formed via the RER process, and their relative strengths with collisional-radiative spectral models. Optical C II RER features are detected in published high-resolution spectra of eight planetary nebulae, and a C III transition has been found in the ultraviolet spectrum in a symbiotic star system. The relative intensities of these lines are consistent with their production by this recombination mechanism. Because RER has not previously been accounted for in photoionized plasmas, its inclusion in models can significantly impact the predicted ionization balance and hence abundance calculations of important astrophysical species. Calculations for C+ suggest that the enhancement in the total recombination rate can amount to a factor of 2.2 at 8100 K, increasing to 7.5 at T = 3500 K. These results demonstrate the importance of including RER in models of photoionized astrophysical plasmas and in elemental abundance determinations.

astro-ph.SR↗

arXiv2019

Automatic phase space generation for Monte Carlo calculations of Intensity Modulated Particle Therapy

Monte Carlo (MC) is generally considered as the most accurate dose calculation tool for particle therapy. However, a proper description of the beam particles kinematics is a necessary input for a realistic simulation. Such a description can be stored in phase space (PS) files for different beam energies. A PS file contains kinetic information such as energies, positions and travelling directions for particles traversing a plane perpendicular to the beam direction. The accuracy of PS files play a critical role in the performance of the MC method for dose calculations. A PS file can be generated with a set of parameters describing analytically the beam kinematics. However, determining such parameters can be tedious and time consuming. Thus, we have developed an algorithm to obtain those parameters automatically and efficiently. In this paper, we present such an algorithm and compare dose calculations using PS automatically generated for the Shanghai Proton and Heavy Ion Center (SPHIC) with measurements. The gamma-index for comparing calculated depth dose distributions (DDD) with measurements are above 96.0% with criterion 0.6%/0.6 mm. For each single energy, the mean difference percentage between calculated lateral spot sizes at 5 different depths and measurements are below 3.5%.

physics.med-ph↗

arXiv2018

Validation of a track repeating algorithm for intensity modulated Carbon therapy with GEANT4

The Fast Dose Calculator (FDC), a track repeating algorithm Monte Carlo method was initially developed for proton therapy. The validation for proton therapy has been demonstrated in a previous work. This method can be expanded to ion applications. Our purpose of this paper is to validate the FDC for carbon therapy. We compare the 3D dose distributions and dose-volume-histograms (DVH) for carbon calculated by FDC with a full Monte Carlo method, GEANT 4. 19 patients in total will be discussed, including 3 patients of prostate, 5 of brain, 3 of head and neck, 4 of lung and 4 of spine. We use gamma-index technique to analyse dose distributions and we do dosimetric analysis for DVH, a more direct and informative quantity for planning system assessment. The FDC calculations of both quantities agree with GEANT4. The gamma-index passing rates of all patients discussed in this paper are above 90% with the criterion 1%/1 mm, above 98% with the criterion 2%/2 mm and over 99.9% with the criterion 3%/3 mm. The Root Mean Square (RMS) of percent difference of dosimetric indices D02, D05, D50, D95 and D98 are 0.75%, 0.70%, 0.79%, 0.83% and 0.76%. And all the difference are allowed for clinical use.

physics.med-ph↗

arXiv2017

Fine-structure electron-impact excitation of Ne$^{+}$ and Ne$^{2+}$ for low temperature astrophysical plasmas

Collision strengths for electron-impact of fine-structure level excitation within the ground term of Ne$^{+}$ and Ne$^{2+}$ are calculated using the Breit-Pauli, Intermediate Coupling Frame Transformation, and DARC $R$-matrix methods. Maxwellian-averaged effective collision strengths and excitation rate coefficient qij are presented for each. The application of the current calculations is to very low temperature astrophysical plasmas, thus we examine the sensitivity of the effective collision strengths down to 10 K. The use of the various theoretical methods allows us to place estimated uncertainties on the recommended effective collision strengths. We also investigate the sensitivity of the collision strengths to the resonance positions and underlying atomic structure. Good agreement is found with previous R-matrix calculations at higher temperature.

physics.atom-ph↗