Practical reconstruction protocol for quantitative ⁹⁰Y bremsstrahlung SPECT/CT

Abstract

Purpose: To develop a practical background compensation (BC) technique to improve quantitative 90 Y-bremsstrahlung single-photon emission computed tomography (SPECT)/computed tomography (CT) using a commercially available imaging system. Methods: All images were acquired using medium-energy collimation in six energy windows (EWs), ranging from 70 to 410 keV. The EWs were determined based on the signal-to-background ratio in planar images of an acrylic phantom of different thicknesses (2-16 cm) positioned below a 90 Y source and set at different distances (15-35 cm) from a gamma camera. The authors adapted the widely used EW-based scatter-correction technique by modeling the BC as scaled images. The BC EW was determined empirically in SPECT/CT studies using an IEC phantom based on the sphere activity recovery and residual activity in the cold lung insert. The scaling factor was calculated from 20 clinical planar 90 Y images. Reconstruction parameters were optimized in the same SPECT images for improved image quantification and contrast. A count-to-activity calibration factor was calculated from 30 clinical 90 Y images. Results: The authors found that the most appropriate imaging EW range was 90-125 keV. BC was modeled as 0.53× images in the EW of 310-410 keV. The background-compensated clinical images had higher image contrast than uncompensated images. The maximum deviation of their SPECT calibration in clinical studies was lowest (<10%) for SPECT with attenuation correction (AC) and SPECT with AC + BC. Using the proposed SPECT-with-AC + BC reconstruction protocol, the authors found that the recovery coefficient of a 37-mm sphere (in a 10-mm volume of interest) increased from 39% to 90% and that the residual activity in the lung insert decreased from 44% to 14% over that of SPECT images with AC alone. Conclusions: The proposed EW-based BC model was developed for 90 Y bremsstrahlung imaging. SPECT with AC + BC gave improved lesion detectability and activity quantification compared to SPECT with AC only. The proposed methodology can readily be used to tailor 90 Y SPECT/CT acquisition and reconstruction protocols with different SPECT/CT systems for quantification and improved image quality in clinical settings. C

Characterization of 90Y‐SPECT/CT self‐calibration approaches on the quantification of voxel‐level absorbed doses following 90Y‐microsphere selective internal radiation therapy

“…Investigators have reported on the positive role of 90 Y planar and 90 Y bremsstrahlung SPECT/CT in disease management after 90 Y‐SIRT . Furthermore, 90 Y SPECT/CT also facilitates dosimetry at the voxel level that allows for investigations into the volume distribution of absorbed doses in tumors and normal liver tissue . A number of approaches have been described in the literature for generation and quantitation of 90 Y bremsstrahlung SPECT/CT, as described in a recent review article .…”

“…A number of approaches have been described in the literature for generation and quantitation of 90 Y bremsstrahlung SPECT/CT, as described in a recent review article . Some of the approaches for 90 Y SPECT quantitation include Monte Carlo‐based modeling of SPECT corrections and reconstructions to multiple energy window–based scatter compensations …”

SPECT/CT image‐based dosimetry for Yttrium‐90 radionuclide therapy: Application to treatment response

“…Since β‐radiation emitted by 90 Y interacts with body tissues resulting in Bremsstrahlung radiation, SPECT/CT has traditionally been regarded as the gold‐standard modality to image the biodistribution of this radionuclide. However, the low photon yield and continuous nature of the Bremsstrahlung x‐ray spectrum make SPECT imaging involving 90 Y technically challenging 17. On the other hand, the 90 Y decay to the 0 + excited state and then ground state of 90 Zr may result in emission of a positron‐electron pair.…”

“…For therapy, 90 Y glass microspheres (TheraSphere, BTG Inc., Ottawa, Canada) were administered with an activity calculated according to the manufacturer's specifications 3. Within 90 min after the administration of the 90 Y, a bremsstrahlung SPECT/CT was acquired using a Siemens Symbia T6 (Siemens Medical Solutions Inc., Malvern, PA) with an energy window of 90–125 keV based on a highly optimized acquisition and reconstruction protocol published by Siman et al 17. The SPECT projection images were acquired with a matrix size of 128 × 128, 4.8 mm pixel size, 28 s/view for 128 views over 360°.…”

“…The SPECT projection images were acquired with a matrix size of 128 × 128, 4.8 mm pixel size, 28 s/view for 128 views over 360°. The SPECT images were reconstructed using the manufacturer's three‐dimensional ordered subset expectation maximization algorithm (Flash3D, Siemens) using 8 iterations with 16 subsets, geometric collimator response modeling, CT‐based attenuation correction using effective energy of the imaging window, dual‐energy window‐based scatter correction, and a 9.6 mm FWHM postreconstruction Gaussian filter 17. Dosimetry was performed using the 90 Y microsphere dosimetry navigator (RapidSphere) within Velocity (Varian Medical Systems, Atlanta, GA) as illustrated in Fig.…”