⁹⁰Y SPECT/CT quantitative study and comparison of uptake with pretreatment ^99 mTc‐MAA SPECT/CT in radiomicrosphere therapy

Abstract

IntroductionYttrium‐90 (90Y) microsphere post‐treatment imaging reflects the true distribution characteristics of microspheres in the tumor and liver compartments. However, due to its decay spectra profile lacking a pronounced photopeak, the bremsstrahlung imaging for 90Y has inherent limitations. The absorbed dose calculations for 90Y microspheres radiomicrosphere therapy (RMT) sustain a limitation due to the poor quality of 90Y imaging. The aim of this study was to develop quantitative methods to improve the post‐treatment 90Y bremsstrahlung single photon emission tomography (SPECT)/computed tomography (CT) image analysis for dosimetric purposes and to perform a quantitative comparison with the 99mTc‐MAA SPECT/CT images, which is used for theranostics purposes for liver and tumor dosimetry.MethodsPre and post‐treatment SPECT/CT data of patients who underwent RMT for primary or metastatic liver cancer were acquired. A Jasczak phantom with eight spherical inserts of various sizes was used to obtain optimal iteration number for the contrast recovery algorithm for improving 90Y bremsstrahlung SPECT/CT images. Comparison of uptake on 99mTc‐MAA and 90Y microsphere SPECT/CT images was assessed using tumor to healthy liver ratios (TLRs). The voxel dosimetry technique was used to estimate absorbed doses. Absorbed doses within the tumor and healthy part of the liver were also investigated for correlation with administered activity.ResultsImprovement in CNR and contrast recovery coefficients on patient and phantom 90Y bremsstrahlung SPECT/CT images respectively were achieved. The 99mTc‐MAA and 90Y microspheres SPECT/CT images showed significant uptake correlation (r = 0.9, P = 0.05) with mean TLR of 9.4 ± 9.2 and 5.0 ± 2.2, respectively. The correlation between the administered activity and tumor absorbed dose was weak (r = 0.5, P > 0.05), however, healthy liver absorbed dose increased with administered activity (r = 0.8, P = 0.0).ConclusionsThis study demonstrated correlation in mean TLR between 99mTc‐MAA and 90Y microsphere SPECT/CT.

Comparison of 90Y SIRT predicted and delivered absorbed doses using a PSF conversion method

“…Prospective treatment planning with pre-therapy 99m Tc-MAA SPECT has demonstrated a good correlation between tumour dose and response [35] , [36] , [37] . However, studies have shown contrasting findings when investigating the predictive power of the pre-therapy 99m Tc-MAA distribution [16] , [17] , [19] , [20] , [38] , [39] , [40] . To allow direct quantitative comparison between predicted and delivered 90 Y absorbed dose, a novel RCM method was developed to address the differences in partial volume effects between 99m Tc-MAA SPECT and 90 Y bremsstrahlung SPECT images by converting the spatial resolution of the pre-therapy scan data to that of the post-therapy scan data.…”

“…However, there are a number of reasons why this assumption may be flawed which include differences in the size and number of particles administered [12] , the catheter position [13] , [14] , [15] , administration flow rates [13] , [14] , [15] and regional blood flow differences between administrations [16] . Previous studies have compared the pre- and post-therapy imaging [14] , [17] , [18] , [19] , [20] , [21] , with the majority of these studies taking no account of the differences in the partial volume effect of the images [14] , [17] , [18] , [19] . However, Gnesin et al [20] applied recovery coefficients to predicted and delivered absorbed doses to tumours derived from 99m Tc-MAA SPECT and 90 Y PET images respectively, while a recent study by Mikell et al [21] convolved 90 Y PET images with a Gaussian function to match the spatial resolution of 99m Tc-MAA SPECT images.…”