Validation Calibration Factor of Single Photon Emission Computed Tomography for Iodine-131 using Non-Spherical Targeted Volume

Abstract

Absolute quantification of Iodine-131 (¹³¹I) on Single Photon Emission Computed Tomography (SPECT) imaging is extremely necessary for the lesion dose per administrative differentiated thyroid cancer procedure. However, non-quantitative SPECT imaging makes determining the dose required for a tumour to be treated is challenging. This multi-vendor and multi-centre research uses phantom measures to assess the quantitative accuracy and inter-system variability of various SPECT/CT systems. Hence, this study aims to determine the calibration factor (CF) for ¹³¹I activity quantification using the National Electrical Manufacturer Association (NEMA) phantom uptake for the Philips BrightView XCT modality. The accuracy activity concentration for a non-spherical targeted volume is less than 15% compared to a spherical targeted volume (<9%). Furthermore, the CF has no significant difference in the value between the matrix sizes of 64×64, 128×128, and 256×256. Therefore, the gamma camera CF must be precisely determined to convert the reconstructed images' counts into activity values for quantitative imaging. However, the NEMA phantom with spherical geometrical is the standard tool for determining CF, the various geometrical shapes other than spherical should be considered for determining CF because the effect of photon distribution contribution is different for any different lesion geometrical.