arXiv subjects

Shih-Chang Lee

Publications and source records attributed to Shih-Chang Lee.

14 recordsLinked to original sources

arXiv2022

Direct mapping from PET coincidence data to proton-dose and positron activity using a deep learning approach

$Objective$. Obtaining the intrinsic dose distributions in particle therapy is a challenging problem that needs to be addressed by imaging algorithms to take advantage of secondary particle detectors. In this work, we investigate the utility of deep learning methods for achieving direct mapping from detector data to the intrinsic dose distribution. $Approach$. We performed Monte Carlo simulations using GATE/Geant4 10.4 simulation toolkits to generate a dataset using human CT phantom irradiated with high-energy protons and imaged with compact in-beam PET for realistic beam delivery in a single-fraction ($\sim$2Gy). We developed a neural network model based on conditional generative adversarial networks to generate dose maps conditioned on coincidence distributions in the detector. The model performance is evaluated by the mean relative error, absolute dose fraction difference, and shift in Bragg peak position. $Main$ $results$. The relative deviation in the dose and range of the distributions predicted by the model from the true values for mono-energetic irradiation between 50 MeV and 122 MeV lie within 1% and 2%, respectively. This was achieved using $\mathrm{10^5}$ coincidences acquired five minutes after irradiation. The relative deviation in the dose and range for spread-out Bragg peak distributions were within 1% and 2.6% uncertainties, respectively. $Significance$. An important aspect of this study is the demonstration of a method for direct mapping from detector counts to dose domain using the low count data of compact detectors suited for practical implementation in particle therapy. Including additional prior information in the future can further expand the scope of our model and also extend its application to other areas of medical imaging.

physics.ins-det↗

arXiv2022

New approaches to particle induced prompt gamma imaging

The distribution of the prompt gamma emissions induced by proton interactions in a target material carries information concerning the proton range and target composition. In order to image prompt gamma we present different approaches. The first approach is based on knife-edge collimator utilized in tandem with a compact PET type detector in order to verify proton range by measuring the depth distribution of prompt gamma relying on Compton scattered events. A second approach aims at unambiguously identifying the presence of protons in a region of interest by introducing a bio-compatible fiducial marker in the patient and measuring the characteristic prompt gamma of the marker against background material. A third approach illustrates a novel design for position sensitive gamma imaging with a millimeter level adjustable position resolution with a high detection efficiency which is a step towards 3D prompt gamma imaging, useful to better understand the target composition. Simulations of the designs were performed using GATE/Geant4 Monte Carlo framework. Experimental tests on fiducial marker were conducted at the proton facilities in INER and Chang Gung Memorial hospital. Using the knife-edge PET approach a range verification of 0.7 mm can be achieved for shifts within 1 cm near the tumor region and up to 4 mm for shifts within a 4 cm window. For the fiducial marker approach we identify 984 keV as the dominant prompt gamma and show that for the 50% relative PG intensity, the R80 position falls within a 3 mm thick 48Ti marker. Using the position sensitive gamma imaging approach we present a feasible design to achieve spatial resolution values of 2.6 mm with a detection efficiency of 5.4E-6 at 6.1 MeV and up to eight depth positions in a single run. The relative advantage of these methods and the challenges in the implementation are discussed.

physics.ins-det↗

arXiv2012

Continuous simulation of hypothetical physics processes with multiple free parameters

We propose a new approach to simulate hypothetical physics processes which are defined by multiple free parameters. Compared to the conventional grid-scan approach, the new method can produce accurate estimations of the detector acceptance and signal event yields continuously over the parameter space with fewer simulation events. The performance of this method is illustrated with two realistic cases.

hep-ex↗

arXiv2011

A program for the Bayesian Neural Network in the ROOT framework

We present a Bayesian Neural Network algorithm implemented in the TMVA package, within the ROOT framework. Comparing to the conventional utilization of Neural Network as discriminator, this new implementation has more advantages as a non-parametric regression tool, particularly for fitting probabilities. It provides functionalities including cost function selection, complexity control and uncertainty estimation. An example of such application in High Energy Physics is shown. The algorithm is available with ROOT release later than 5.29.

physics.data-an↗

arXiv2001

Λ_b \to ΛJ/ψdecay in perturbative QCD

We calculate the amplitudes involved in the heavy baryon nonleptonic decay $Λ_b \rar ΛJ/ψ$ using perturbative QCD factorization theorem, which are expressed as convolutions of hard $b$ quark decay amplitudes with the $Λ_b$ baryon, $Λ$ baryon and $J/ψ$ meson distribution amplitudes. It is found that nonfactorizable contributions dominate over factorizable ones. Because of soft cancellation in pairs of nonfactorizable diagrams, the $Λ_b \rar ΛJ/ψ$ decay is characterized by a large scale, such that perturbative QCD is applicable. Employing the distribution amplitudes determined in our previous works and from QCD sum rules, we derive the branching ratio $B(Λ_b \rar ΛJ/ψ)=(1.7 \sim 5.3)\times 10^{-4}$ in agreement with data. We predict an asymmetry parameter $α= -0.17 \sim -0.14$ associated with the anisotropic angular distribution of the $Λ$ baryons produced in polarized $Λ_b$ baryon decays.

hep-ph↗

arXiv2000

Polarized $Λ_b\to Λ_c l \barν$ decay in perturbative QCD

We study the polarized $Λ_b$ baryon semileptonic decay $Λ_b \to Λ_cl{\barν}$ using perturbative QCD factorization theorem. In this approach heavy baryon transition form factors are expressed as the convolutions of hard $b$ quark decay amplitudes with universal $Λ_b$ and $Λ_c$ baryon wave functions. With the heavy baryon wave functions determined in our previous work, we predict the asymmetry parameter $α({\hat e})\equiv (N_+-N_-)/(N_++N_-)=-0.31 {\bf P}\cdot{\hat e}$, where ${\bf P}$ is the $Λ_b$ baryon polarization, ${\hat e}$ a unit vector perpendicular to the $Λ_b$ baryon momentum, $N_+$ ($N_-$) the number of leptons whose momenta possess positive (negative) components along ${\hat e}$. This result is useful for extracting the transverse polarization of a $Λ_b$ baryon from data of exclusive semileptonic decays.

hep-ph↗

arXiv1999

Applicability of perturbative QCD to $Λ_b \to Λ_c$ decays

We develop perturbative QCD factorization theorem for the semileptonic heavy baryon decay $Λ_b \to Λ_c l\barν$, whose form factors are expressed as the convolutions of hard $b$ quark decay amplitudes with universal $Λ_b$ and $Λ_c$ baryon wave functions. Large logarithmic corrections are organized to all orders by the Sudakov resummation, which renders perturbative expansions more reliable. It is observed that perturbative QCD is applicable to $Λ_b \to Λ_c$ decays for velocity transfer greater than 1.2. Under requirement of heavy quark symmetry, we predict the branching ratio $B(Λ_b \to Λ_c l{\barν})\sim 2%$, and determine the $Λ_b$ and $Λ_c$ baryon wave functions.

hep-ph↗

arXiv1998

The $Λ_b\to pl{\barν}$ decay in perturbative QCD

We develop perturbative QCD factorization theorems for the exclusive semileptonic heavy baryon decay $Λ_b \to pl{\barν}$, in which the relevant hadronic form factor is expressed as the convolution of a hard subamplitude with the $Λ_b$ baryon wave function and the proton wave function. The specific evolution scale for the proton wave function, determined from the best fit to the data of the proton form factor, is adopted. The Sudakov resummation for a heavy-light system (the $Λ_b$ baryon) and the quark-level decay diagrams with at least one hard gluon attaching the $b$ quark, which were ignored in the literature, are incorporated. It turns out that these additional ingredients are important: the neglect of the former and the latter reduces the results of the form factor by factors 1.5 and 3, respectively. We present the predictions of the form factor and of the proton energy spectrum for the various choices of the parameter involved in the $Λ_b$ baryon wave function.

hep-ph↗

arXiv1996

Exact Solution of Frenkel-Kontorova Models with a Complete Devil's Staircase in Higher Dimensions

We solve exactly a class of Frenkel-Kontorova models with piecewise parabolic potential, which has $d$ sub-wells in a period. With careful analysis, we show that the phase diagram of the minimum enthalpy configurations exhibits the structure of a complete $d$-dimensional devil's staircase. The winding number of a minimum enthalpy configuration is locked to rational values, while the fraction of atoms in each sub-well is locked to values which are sub-commensurable with the winding number.

solv-int↗

arXiv1996

Farey Tree and the Frenkel-Kontorova Model

We solved the Frenkel-Kontorova model with the potential $V(u)= -\frac{1}{2} |λ|(u-{\rm Int}[u]-\frac{1}{2})^2$ exactly. For given $|λ|$, there exists a positive integer $q_c$ such that for almost all values of the tensile force $σ$, the winding number $ω$ of the ground state configuration is a rational number in the $q_c$-th level Farey tree. For fixed $ω=p/q$, there is a critical $λ_c$ when a first order phase transition occurs. This phase transition can be understood as the dissociation of a large molecule into two smaller ones in a manner dictated by the Farey tree. A kind of ``commensurate-incommensurate'' transition occurs at critical values of $σ$ when two sizes of molecules co-exist. ``Soliton'' in the usual sense does not exist but induces a transformation of one size of molecules into the other.

solv-int↗

arXiv1995

On the Observation of Top Spin Correlation Effect at Tevatron

We propose to observe the top spin correlation effect at Tevatron through the measurement of the correlated asymmetries of the charged lepton momenta using the dilepton decay events of top and anti-top quark pairs. The possibility of reconstructing the events and observing the asymmetries at 3$σ$ level with projected luminosity of the Tevatron for Run II is demonstrated by simulation. The effect can provide the first direct measurement of the spin of a quark.

hep-ph↗

arXiv1995

Transfer Matrix Method in Sandpile Models

We present a transfer matrix method which is particularly useful for solving some classes of sandpile models. The method is then used to solve the deterministic nonabelian sandpile models for N=2 and N=3. The possibility of generalization to arbitrary N is discussed briefly.

cond-mat↗

arXiv1995

Exact Solution of an One Dimensional Deterministic Sandpile Model

Using the transfer matrix method, we give the exact solution of a deterministic sandpile model for arbitrary $N$, where $N$ is the size of a single toppling. The one- and two-point functions are given in term of the eigenvalues of an $N \times N$ transfer matrix. All the n-point functions can be found in the same way. Application of this method to a more general class of models is discussed. We also present a quantitative description of the limit cycle (attractor) as a multifractal.

cond-mat↗

arXiv1995

The Effect of Top Quark Polarization at Hadronic Colliders

We derive a simple analytic expression for q \bar{q}, g g -> t \bar{t} -> b W^+ \bar{b} W^- -> b \bar{l} ν_l \bar{b} l' \bar{ν_{l'}} for on shell intermediate states with the interference effects due to the polarizations of the t and \bar{t}. We then investigate how this effect may be measured at Tevatron or other hadronic colliders.

hep-ph↗