Prompt Gamma-Ray Imaging

L. Xu and R. P. Gardner

North Carolina State University, Raleigh, NC, 27695, Email: Gardner@ncsu.edu

ABSTRACT

A new imaging modality called prompt gamma-ray imaging (PGI) has been identified and investigated primarily by Monte Carlo simulation. This approach consists of irradiating objects in a thermal neutron beam of a nuclear reactor to produce prompt gamma rays from the elements in the objects by neutron capture (n,γ) reactions. These prompt gamma rays are emitted in energies that are characteristic of each element and they are also produced in characteristic coincident chains. After measuring these prompt gamma rays by a surrounding spectrometry array, the distribution of each element of interest in the object is reconstructed from the mapping of each detected signature gamma ray, by either electronic or mechanical collimation or both. Currently, this approach is proposed for use in Neutron Capture Therapy (NCT) to monitor neutron-capture-reaction rate distributions, which are directly proportional to the dose distribution in the irradiated object.

The primary approach is to use Monte Carlo simulation methods to provide forward models of prompt gamma-ray detection to investigate the feasibility of this new imaging idea. The Geant4-based simulation platform has been developed and used for this purpose. Benchmark experiments have been conducted to test the capability of the code to simulate prompt gamma rays by following the nuclear structures of each irradiated isotope. Coincidence counting techniques have also been treated since they are considered to be the most important future improvement in neutron-related gamma-ray detection applications to reduce the gamma-ray background and improve system signal-to-noise ratios. The common SPECT imaging algorithms are presently being used for image reconstruction.

Keywords PGI, Neutron Capture Therapy, NCT.