Towards a comprehensive validation for Monte Carlo SPECT simulations

Abstract

Aim/Introduction: Monte Carlo (MC) simulations directly track the interactions of each gamma ray emitted from a source and record all instances of scatter and attenuation. They are therefore a valuable tool for the optimisation of acquisition protocols and image corrections in Single-Photon Emission Computed Tomography (SPECT). Accurate image corrections are becoming increasingly important due to the need for quantitative SPECT, and their methodologies are frequently based on results from MC. The results of MC simulations are often used as a ‘ground-truth’, but this is only the case if the simulation is fully validated against experimental data. This work aims to establish a comprehensive validation for a MC SPECT simulation. Materials and Methods: A full MC simulation of the Mediso AnyScan SPECT system installed at the National Physical Laboratory has been developed in the GATE (Geant4 Application for Tomographic Emission) toolkit [1]. The simulation models the components of each detector head and the collimators according to technical specifcations provided. The simulation can run in both dual- and triple-head acquisition modes. Experimental measurements of detection efciency for a range of energies were collected, permitting an energy-dependent camera efciency to be modelled and applied to the simulation. Validation data have been collected in a range of geometries, including commercial and 3D-printed phantoms, for Lu-177 and Tc-99m. Experimental observables have been considered to verify the simulation output is comparable to that of the physical SPECT system; these include the sensitivity, energy spectra, tomographic acquisition and movement of the detector heads, and the projection images. Results: Quantitative analysis has confrmed that the simulated acquisitions are equivalent to the physical SPECT acquisitions based on the given observables. Conclusion: This work provides a validation protocol which can be applied to any MC SPECT simulation. The validated simulation is now being used to optimise clinical imaging protocols and corrections for the novel isotopes Tb-155 and Tb-161.