Geant4 Simulation Study of Plasma Panel Sensor based ... âFirst Results with a Microcavity Plasma Panel Detectorâ, NIM A (http://arxiv.org/pdf/1407.6491v4.pdf).
Geant4 Simulation Study of Plasma Panel Sensor based Particle-Tracker for Proton Radiography and CT Peter S. Friedman1, Vladimir A. Bashkirov2, Reinhard W. Schulte2 1 Integrated Sensors, LLC, Ottawa Hills, OH 43606, 2 Department of Basic Sciences, Division of Radiation Research, Loma Linda University, Loma Linda, CA 92354
Proton CT is currently being explored with Monte Carlo simulation studies as well as first experimental scanner prototypes as a method to improve the planning and delivery accuracy of particle therapy. The existing scanner prototype (Phase II) built by a collaboration of investigators at Loma Linda University (LLU), UC Santa Cruz, and Baylor University is based on silicon (Si) strip detectors for tracking individual protons through the object to be imaged (a patient in the future clinical application). Si detectors are mainly available up to ~9 cm in side length and thicknesses of 0.3 mm or more, requiring tiling of individual detectors to cover the required relatively large sensitive area and leading to unwanted scattering of tracked protons with possible compromise of spatial resolution. Here we explored the potential use of plasma panel sensors (PPS) for proton tracking in proton radiography and computed tomography (CT) with a Geant4 simulation. PPS are an inherently digital, high gain, novel variant of micropattern gas detectors inspired by many operational and fabrication principles common to plasma display panels. 1,2 The PPS is comprised of a dense array of small, plasma discharge, gas cells within an inert “open” panel envelope (e.g. typically glass), and is assembled from non-reactive, intrinsically radiationhard materials such as glass or ceramic substrates, refractory metal electrodes, and mostly inert gas mixtures. The Geant4 model used in the simulation is shown in Fig.1; it included the proton tracker consisting of two PPS panels installed in a gas-filled sealed chamber with ultrathin entrance and exit windows (i.e., 14 µm foil), a therapeutic proton beam line, and a water tank where the beam was stopped. Three possible gas mixtures (90%CF4/10%CO2, 70%Ar/30%CO2, and 70%Ar/30%CF4) were simulated. The detector pixel pitch defined by the internal hexagonal cell structure of the panel was set to either: 150, 300 or 500 µm. The gas gap between the front and back substrates was 2 mm. The simulation results for the energy deposition in the PPS (# of ion pairs) show that for the 90% CF4 / 10% CO2 mixture the proton detection efficiency per panel should be very close to 100%, and for both other mixtures better than 99%. The simulated track reconstruction 20 cm downstream from the PPS tracker is comparable (for 300 µm pitch) or superior ( 0.49 mm for pitch of 150 µm, Fig. 2) to that of the Si microstrip telescope currently installed in the Phase II pCT scanner at LLU ( 0.68 mm for pitch of 238 µm, Fig. 2). The simulation of the PPS shows promising results for applications in proton radiography and CT. These need to be validated by experimental studies.
Fig. 1. Simulation geometry.
1 2
Fig. 2. Track reconstruction accuracy 20 cm downstream from PPS tracker (left) and Si telescope (right).
R. Ball et al., “Development of a Plasma Panel Radiation Detector”, NIM A, 764 (2014) 122-132. R. Ball et al., “First Results with a Microcavity Plasma Panel Detector”, NIM A (http://arxiv.org/pdf/1407.6491v4.pdf).
Funded by NIH/NCI grant 1R43 CA183437 01.
