Fast technetium‐99m liver SPECT for evaluation of the pretreatment procedure for radioembolization dosimetry

Abstract

Purpose: The efficiency of radioembolization procedures could be greatly enhanced if results of the 99m Tc-MAA pretreatment procedure were immediately available in the interventional suite, enabling 1-day procedures as a result of direct estimation of the hepatic radiation dose and lung shunt fraction. This would, however, require a relatively fast, but still quantitative, SPECT procedure, which might be achieved with acquisition protocols using nonuniform durations of the projection images. Methods: SPECT liver images of the 150-MBq 99m Tc-MAA pretreatment procedure were simulated for eight different lesion locations and two different lesion sizes using the digital XCAT phantom for both single-and dual-head scanning geometries with respective total acquisition times of 1, 2, 5, 10, and 30 min. Three nonuniform projection-time acquisition protocols ("half-circle SPECT (HCS)," "nonuniform SPECT (NUS) I," and "NUS II") for fast quantitative SPECT of the liver were designed and compared with the standard uniform projection-time protocol. Images were evaluated in terms of contrast-tonoise ratio (CNR), activity recovery coefficient (ARC), tumor/non-tumor (T/N) activity concentration ratio, and lung shunt fraction (LSF) estimation. In addition, image quality was verified with a physical phantom experiment, reconstructed with both clinical and Monte Carlo-based reconstruction software. Results: Simulations showed no substantial change in image quality and dosimetry by usage of a nonuniform projection-time acquisition protocol. Upon shortening acquisition times, CNR dropped, but ARC, T/N ratio, and LSF estimates were stable across all simulated acquisition times. Results of the physical phantom were in agreement with those of the simulations. Conclusion: Both uniform and nonuniform projection-time acquisition liver SPECT protocols yield accurate dosimetric metrics for radioembolization treatment planning in the interventional suite within 10 min, without compromising image quality. Consequently, fast quantitative SPECT of the liver in the interventional suite is feasible.

A Monte Carlo study to investigate the feasibility of an on‐board SPECT/spectral‐CT/CBCT imager for medical linear accelerator

“…The relatively long scanning time for SPECT imaging of the OBI system might rely on the advance of fast SPECT acquisition techniques and region of interest (ROI) SPECT acquisition methods including the emerging AI techniques to translate this design to clinical implementation. 31,32 A previous study reported that fast pretreatment liver SPECT scans within 10 min were achieved based on parallel hole collimators without compromising quantitative image quality in the interventional suite. 31 This scanning time can be further reduced by using focusing collimators (such as cone-beam collimators) with an ultrahigh sensitivity without sacrificed imaging spatial resolution at the expense of smaller FOV, which is not questionable for ROI scans of SPECT in RT applications.…”

“…31,32 A previous study reported that fast pretreatment liver SPECT scans within 10 min were achieved based on parallel hole collimators without compromising quantitative image quality in the interventional suite. 31 This scanning time can be further reduced by using focusing collimators (such as cone-beam collimators) with an ultrahigh sensitivity without sacrificed imaging spatial resolution at the expense of smaller FOV, which is not questionable for ROI scans of SPECT in RT applications. 32 To shorten SPECT image reconstruction time, the FBP algorithm was chosen with the reasons described in Appendix C8.…”

Streamlining TARE or personalizing SIRT? Different philosophies to treat different HCCs with Yttrium-90…

“…Other approaches have also been developed to streamline TARE, such as faster SPECT analysis. 12 However, we believe that streamlining might not be the only way to improve the diffusion of the technique, and we would like to stress that the usefulness of MAA-SPECT is not limited to the search for LSF or extrahepatic deposits. Our team and others have for several years worked around the very straightforward notion that response to SIRT treatment is related to the dose delivered to the tumor 13,14 As SIRT is a radiation therapy, one might be surprised to learn that the current way to prescribe glass-microspheres is based on the dose delivered to the injected liver (considering in the same volume tumor and non-tumoral tissues), and for resin-microspheres on the body surface area.…”

Technical Development of Interventional Nuclear Imaging

“…This argument similarly holds for regions of increasingly smaller sizes. We acknowledge that high visual quality is currently not crucial for dosimetry, as activity recovery remains accurate for low count rates as with gating [37]. However, it could be argued that uniformity will become an increasingly important measure when voxel-based dosimetry [38] is further developed, as the activity will then also need to be correctly measured for small regions.…”

“…The image quality phantom consisted of the spheres from a regular image quality (IQ) phantom (37,28,22,17,13, and 10 mm diameter) (IEC NEMA 2007) in their usual pattern, but they were enclosed in a different cylinder (Hoffman Brain phantom). The latter was used because it is somewhat smaller than the regular IQ enclosing, which ensured that no truncation effects affected the acquisition.…”