Geant4-based Monte Carlo Simulation Research Articles

GPU-acceleration of GEANT4-based Monte Carlo Simulations for Radio Therapy

GPU-acceleration of GEANT4-based Monte Carlo Simulations for Radio Therapy

SU‐GG‐I‐31: Comparison of Breast‐Centered and Volume‐Of‐Interest (VOI)‐Centered VOI Cone Beam CT Techniques — Dose and Scatter Considerations with Monte Carlo Simulation

Purpose: To evaluate and compare dose saving and scatter reduction properties of VOI‐centered and breast‐centered approaches to VOI cone beam CT with Monte Carlo simulation. Method and Materials: To implement the VOI scanning technique, a mask with an opening is inserted between the x‐ray source and the patient to deliver higher exposures inside the VOI and lower exposures outside the VOI during the scan. There are two approaches to implement this technique. One is to center the breast with the rotation axis and move the VOI mask to track the VOI. The other is to center the VOI with the rotation axis, thus keeping the VOI mask fixed during the scan. A cylindrical breast model with a VOI close to the breast boundary was constructed to evaluate and compare the two approaches with Geant4 based Monte Carlo simulation. Dose distribution in the breast and scatter‐to‐primary ratios (SPRs) at the detector input were evaluated and compared to those estimated for full field cone beam CT. Results: Both VOI scanning techniques significantly reduce the radiation doses and scatter intensities both inside and outside the VOI. However, dose saving with the breast‐centered approach was approximately twice as much as that with the VOI‐centered approach both inside and outside the VOI. SPRs inside the VOI were similar for the two approaches and varied little with rotation degree. Conclusion: The breast‐centered scan appears to be the preferred approach to VOI cone beam CT because it resulted in substantially better dose saving while similar scatter reduction as compared to the VOI centered approach. Effort to implement this technique is underway to demonstrate this technique and to validate the simulation results.Acknowledgement: This work was supported in part by grants CA104759 and CA124585 from NIH‐NCI, a grant EB00117 from NIH‐NIBIB, and a subcontract from NIST‐ATP.

Coherent radio pulses from showers in different media: A unified parametrization

We study the frequency and angular dependences of Cherenkov radio pulses originated by the excess of electrons in electromagnetic showers in different dense media that are being given consideration as targets for ultra high energy neutrino detection such as ice, salt and the lunar regolith. By means of a simple model of shower development we rederive the scaling of the electric field spectrum with the properties of the media such as density, radiation length, Moli\`ere radius, critical energy and refraction index. We compare the predictions of the scaling relations to the numerical results obtained in our own developed GEANT4-based Monte Carlo simulation, and address in a quantitative manner the predictive power of the scaling relations. We also give a unified parametrization of the frequency spectrum and angular distribution of the electric field in ice, salt, and the lunar regolith, in terms of the relevant properties of the media to be used in practical applications. We establish the applicability of our parametrizations. Our formulas are useful for estimates of the acceptance of current and future neutrino detectors using the radio technique, and for many other practical applications.

SIMULATIONS OF RADIO EMISSION FROM ELECTROMAGNETIC SHOWERS IN DENSE MEDIA

By means of GEANT4-based Monte Carlo simulations, we have studied the frequency and angular behavior of Cherenkov radio pulses originated by the excess charge in electromagnetic (EM) showers in different dense media. We have developed a simple model to relate the main characteristics of the electric field spectrum to the longitudinal and lateral development of the EM showers. Using this model the electric field spectrum is shown to have a scaling behavior with a number of medium parameters. We explore the validity of our model by comparing its predictions against full Monte Carlo simulations.

A study of the water Cherenkov calorimeter

The novel idea of a Cherenkov calorimeter made of water tanks as the next generation neutrino detector for ν factories and ν beams is investigated. A water tank prototype with a dimension of 1 × 1 × 13 m 3 is constructed, its performance is studied and compared with a GEANT4 based Monte Carlo simulation. By using measured parameters of the water tank, including the light collection efficiency, attenuation length, angular dependent response, etc., a detailed Monte Carlo simulation demonstrates that the detector performance is excellent for identifying neutrino charged current events while rejecting neutral current and wrong-flavor backgrounds.

Reconstruction for proton computed tomography by tracing proton trajectories: A Monte Carlo study

Proton computed tomography (pCT) has been explored in the past decades because of its unique imaging characteristics, low radiation dose, and its possible use for treatment planning and on-line target localization in proton therapy. However, reconstruction of pCT images is challenging because the proton path within the object to be imaged is statistically affected by multiple Coulomb scattering. In this paper, we employ GEANT4-based Monte Carlo simulations of the two-dimensional pCT reconstruction of an elliptical phantom to investigate the possible use of the algebraic reconstruction technique (ART) with three different path-estimation methods for pCT reconstruction. The first method assumes a straight-line path (SLP) connecting the proton entry and exit positions, the second method adapts the most-likely path (MLP) theoretically determined for a uniform medium, and the third method employs a cubic spline path (CSP). The ART reconstructions showed progressive improvement of spatial resolution when going from the SLP [2 line pairs (lp) cm(-1)] to the curved CSP and MLP path estimates (5 lp cm(-1)). The MLP-based ART algorithm had the fastest convergence and smallest residual error of all three estimates. This work demonstrates the advantage of tracking curved proton paths in conjunction with the ART algorithm and curved path estimates.

Neutron interactions in AGATA and their influence on [formula omitted]-ray tracking

A GEANT4-based Monte Carlo simulation of the future 4 π γ -ray spectrometer AGATA has been performed. Emphasis was put on studies of neutron interactions, how they affect the γ -ray tracking performance of the array, and if AGATA could be used as a neutron detector. The obtained results show that there is a large probability to detect neutrons in AGATA. Using an energy threshold of 5 keV on the HPGe detector signals, which is the goal for AGATA, the neutron detection efficiency is 40– 50 % and the number of interactions per detected neutron is 3–11, for neutrons with energies in the range 0.5–18 MeV. The depth profile and the distance between nearest-neighboring interaction points have been investigated and were found to be rather similar for neutron and γ -ray-induced events. For neutrons detected in coincidence with γ -rays, the photo-peak efficiency of AGATA was found to be reduced by about 1 % per emitted neutron using existing γ -ray tracking algorithms, while the peak-to-background ratios were reduced to a much larger extent. The possibility to discriminate between detection of neutrons and γ -rays using the time-of-flight technique was evaluated. In addition two new neutron- γ -ray discrimination methods were developed and tested. The first one is based on tracking of γ -rays following inelastic neutron scattering, and the determination of the direction of emission of such γ -rays, which is randomly oriented compared to γ -rays originating from the center of AGATA. The second method makes use of the excess of low-energy interactions produced by the recoiling Ge ions, assigning such interaction points, which are left over after γ -ray tracking has been performed, as being due to neutrons. None of the methods have so far given satisfactory results, which means that further developments regarding the neutron- γ discrimination in AGATA are needed.