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A phantom study: Should 124 I-mIBG PET/CT replace 123 I-mIBG SPECT/CT?

Authors :: Beijst C
de Keizer B
Lam MGEH
Janssens GO
Tytgat GAM
de Jong HWAM
Source :: Medical physics [Med Phys] 2017 May; Vol. 44 (5), pp. 1624-1631. Date of Electronic Publication: 2017 Apr 17.
Publication Year :: 2017
Abstract: Purpose: The isotope <superscript>123</superscript> I is commonly labeled with meta-iodobenzylguanidine (mIBG) for imaging of neuroendocrine tumors, such as pheochromocytomas and neuroblastomas. <superscript>123</superscript> I-mIBG SPECT/CT imaging is performed for staging, follow-up and selection of patients for treatment with <superscript>131</superscript> I mIBG. As an alternative to <superscript>123</superscript> I, <superscript>124</superscript> I-mIBG PET/CT may be used, potentially taking advantage of the superior PET image quality. The purpose of this study was to investigate whether <superscript>124</superscript> I PET/CT improves image quality as compared with <superscript>123</superscript> I SPECT/CT for equal patient effective radiation dose (in mSv).<br />Methods: Phantom measurements were performed using the NEMA-2007 image quality phantom. SPECT and PET reconstruction settings were used with and without time-of-flight (TOF) and point-spread-function (PSF) modeling. As a measure of image quality, the contrast-to-noise ratio (CNR) was calculated. The ratio of the <superscript>123</superscript> I to <superscript>124</superscript> I activity concentration was determined at which the contrast-to-noise ratio was equal for both modalities. This metric was defined as the contrast equivalent activity ratio (CEAR).<br />Results: CEARs of 47.7, 25.6, 23.1, 14.6, 10.0, and 9.1 were obtained for a TOF and PSF modeled <superscript>124</superscript> I reconstruction method and an attenuation and scatter-corrected <superscript>123</superscript> I reconstruction method for sphere sizes of 10 to 37 mm, respectively. As the effective radiation dose of <superscript>124</superscript> I-mIBG is higher than of <superscript>123</superscript> I-mIBG (in mSv/MBq), an equal effective dose corresponds to a CEAR of 5 to 10. Therefore, CEARs higher than 5 to 10 indicate that <superscript>124</superscript> I PET/CT outperforms <superscript>123</superscript> I SPECT/CT in the sense of image quality for equal patient effective radiation dose.<br />Conclusion: The CEAR is much larger than a factor of 5 to 10 (needed for equal patient effective radiation dose) for most of the reconstruction methods and sphere sizes. Therefore, <superscript>124</superscript> I-mIBG PET/CT is expected to improve image quality and/or may be used to reduce effective patient dose as compared with <superscript>123</superscript> I-mIBG SPECT/CT.<br /> (© 2017 American Association of Physicists in Medicine.)