Determination of energy windows for the triple energy window scatter correction method in I-131 on a Siemens SYMBIA gamma camera: a GATE simulation study

Image correction for scattered photons is important for the quantification of gamma-camera imaging using I-131. Many previous studies have addressed this issue but none have compared scattered photon fractions of I-131 with varying energy windows, to determine optimal main- and sub-energy windows for the implementation of TEW correction in I-131 imaging. We assessed the scattered photon fractions and determined the optimal main- and sub- energy windows for TEW in I-131 using a Siemens SYMBIA T2 SPECT/CT using a Monte Carlo method (GATE simulation). To validate the GATE simulation code, we compared the spatial resolutions obtained experimentally and from GATE simulation, for I-123 and Tc-99m. A high-energy general purpose (HE) collimator was used to assess the scattered photon fractions measured with the I-131 radioisotope placed at eight different field-of-view locations in a water phantom (diameter 16 cm, length 32 cm), and at the center in air. To implement the TEW (triple energy window) method, two different main-energy window widths (15 and 20%) and two different sub-energy window widths (3 and 5 keV) were used. The experimental measurement and simulation results exhibited a similar pattern with < 15% difference in spatial resolution with increasing distance. The I-131 scatter fraction with 15% of the main-energy window and 5 keV sub-energy windows was similar to the ''goldstandard'' scatter fraction. Main- and sub-energy window selection for the TEW correction in I-131 is important to avoid over- or under-correction in the scatter fraction. A 15% of main energy window with 5 keV sub-energy windows were found to be optimal for implementation of the TEW method in I-131. This result provides the optimal energy window for I-131 scintigraphy data and will aid the quantification of I-131 imaging