ABSTRACT
Online monitoring of the stopping distribution of particle beams used for radiotherapy provides the possibility of detecting possible errors in dose deposition early during a given treatment session, and may therefore help to improve the quality of the therapy. Antiproton annihilation events produce several long-range secondary particles which can be detected in real time by standard high energy particle physics detector systems. In this note, Monte Carlo calculations are performed in order to study the feasibility of real-time imaging by detecting charged pions produced during antiproton irradiation of typical biological targets. A simple treatment plan in a water phantom is simulated and the results show that by detecting pi+/- the position and the size of the planned target volume can be located with precision in the order of 1 mm.
Subject(s)
Diagnostic Imaging , Proton Therapy , Radiometry/methods , Models, Biological , Monte Carlo Method , Radiotherapy Dosage , Time FactorsABSTRACT
Monte Carlo simulations are increasingly used in scintigraphic imaging to model imaging systems and to develop and assess tomographic reconstruction algorithms and correction methods for improved image quantitation. GATE (GEANT4 application for tomographic emission) is a new Monte Carlo simulation platform based on GEANT4 dedicated to nuclear imaging applications. This paper describes the GATE simulation of a prototype of scintillation camera dedicated to small-animal imaging and consisting of a CsI(Tl) crystal array coupled to a position-sensitive photomultiplier tube. The relevance of GATE to model the camera prototype was assessed by comparing simulated 99mTc point spread functions, energy spectra, sensitivities, scatter fractions and image of a capillary phantom with the corresponding experimental measurements. Results showed an excellent agreement between simulated and experimental data: experimental spatial resolutions were predicted with an error less than 100 microns. The difference between experimental and simulated system sensitivities for different source-to-collimator distances was within 2%. Simulated and experimental scatter fractions in a [98-182 keV] energy window differed by less than 2% for sources located in water. Simulated and experimental energy spectra agreed very well between 40 and 180 keV. These results demonstrate the ability and flexibility of GATE for simulating original detector designs. The main weakness of GATE concerns the long computation time it requires: this issue is currently under investigation by the GEANT4 and the GATE collaborations.
Subject(s)
Gamma Cameras , Animals , Computer Simulation , Image Processing, Computer-Assisted , Monte Carlo Method , Normal Distribution , Phantoms, Imaging , Scattering, Radiation , Sensitivity and Specificity , SoftwareABSTRACT
The results of studies conducted with a small field of view tomographic gamma camera based on a Position Sensitive Photomultiplier Tube are reported. The system has been used for the evaluation of radiopharmaceuticals in small animals. Phantom studies have shown a spatial resolution of 2mm in planar and 2-3mm in tomographic imaging. Imaging studies in mice have been carried out both in 2D and 3D. Conventional radiopharmaceuticals have been used and the results have been compared with images from a clinically used system.
Subject(s)
Bombesin/pharmacokinetics , Neoplasms, Experimental/diagnostic imaging , Radiopharmaceuticals/pharmacokinetics , Technetium/pharmacokinetics , Algorithms , Animals , Gamma Cameras , Image Processing, Computer-Assisted/instrumentation , Kidney/diagnostic imaging , Mice , Mice, Nude , Radionuclide Imaging , Sensitivity and Specificity , Signal Processing, Computer-Assisted/instrumentation , Technetium/chemistryABSTRACT
This paper investigates the possibility of developing a SPECT system that combines the high spatial resolution of position sensitive photomultiplier tubes (PSPMTs) with the excellent performance of iterative reconstruction algorithms. A small field of view (FOV) camera based on a PSPMT and a pixelized scintillation crystal made of CsI(Tl) have been used for the acquisition of the projections. With the use of maximum likelihood expectation maximization (ML-EM) and ordered subsets expectation maximization (OSEM) slices of the object are obtained while three-dimensional (3D) reconstruction of the object is carried out using a modified marching cubes (MMC) algorithm. The spatial resolution of tomographic images obtained with the system was 2-3mm. The spatial resolution of a conventional system that uses filtered backprojection (FBP) for slices reconstruction was more than 9 mm.
