Segmental Perfusion Differences on Paired Tc-99m Macroaggregated Albumin (MAA) Hepatic Perfusion Imaging and Yttrium-90 (Y-90) Bremsstrahlung Imaging Studies in SIR-Sphere Radioembolization: Associations with Angiography

Abstract

Surgically unresectable primary and metastatic liver tumors have been increasingly treated with Y-90 radioembolization. In preparation for Y-90 radioembolization therapy, a baseline angiogram and a Tc-99m MAA hepatic perfusion study simulating Y-90 microsphere infusion are routinely performed, followed by a 2 nd angiogram in which the catheter is positioned in the same position as during the baseline angiography. However, radiotracer distribution on paired Tc-99m MAA hepatic perfusion imaging and post-therapy Y-90 bremsstrahlung imaging studies does not always match. The purpose of this study was to examine perfusion differences or mismatch which involve hepatic segment(s) and to identify underlying causes by correlating with angiography. 81 paired Tc-99m MAA hepatic perfusion imaging and post-therapy Y-90 bremsstrahlung imaging studies and corresponding angiograms were reviewed. 31 studies showed segmental perfusion differences (SPDs). SPDs were less frequently observed with infusion into the left hepatic artery (LHA) as compared to the proper (PHA) and right hepatic artery (RHA) (P<0.05). Significant associations were found with differences in catheter tip position between the two angiograms (P<0.001), catheter tip in proximity to an arterial bifurcation (P<0.01) or a small branch (P<0.01). Differences in catheter position, in combination with proximity to an arterial bifurcation or an arterial branch showed strong association with SPDs (P<0.001). In conclusion, when the catheter tip is in proximity to an arterial bifurcation or a branch, subtle differences in its position can alter microsphere perfusion or trajectory to the target vessels, which can be demonstrated by segmental perfusion mismatch on paired Tc-99m MAA hepatic perfusion imaging and posttherapy Y-90 bremsstrahlung imaging studies.

Reply: Results Confounded by a Disregard for Basic Dose–Response Radiobiology

“…99m Tc-MAA scintigraphy may be considered a 'simulation study' for 90 Y resin microsphere predictive dosimetry" (supplemental data of (2)), yet he acknowledges in his letter that " 99m Tc-MAA is an imperfect surrogate for 90 Y microspheres." The latter assumption is well in line with the evidence from several other studies that investigated 99m Tc-MAA and 90 Y microsphere distribution in different tumor entities (3)(4)(5)(6). Consequently, relating 99m Tc-MAA distribution to the accumulated dose is a questionable practice.…”

A review of 3D image-based dosimetry, technical considerations and emerging perspectives in 90Y microsphere therapy

“…A study of RMS in 39 patients (with both HCC & metastatic lesions) segmented the liver into segments, and showed that for 68% of all segments (n=225), a difference of >10% between MAA and MS activity distribution was found, and that in every procedure at least 1 segment showed a >10% difference [58]. A similar study of 81 patients with a mix of HCC and metastases treated with RMS showed 31 patients had segmental perfusion differences, influenced highly by catheter position [75]. A recent study of 18 HCC patients treated with RMS found that the ratio of MAA to MS uptake in the tumour was 1.4:1, indicating that using MAA imaging for dosimetry calculations can overestimate D T [76].…”

“…Surgical procedures have been identified as a cause of MAA-MS mismatch such as differences in injection rates, microcatheter positioning [75] and arterial flow hemodynamics [23]. A 5-10 mm difference in catheter position between tip and artery opening has been shown to have a major impact on microsphere flow distribution [58,77].…”

Multiagent imaging of liver tumors with reference to intra-arterial radioembolization

“…The number of albumin particles is significantly lower than the number of injected 90 Y-microspheres (0.1-0.2 millions of MAA versus 30-60 millions of resin and 4-5 millions of glass particles), and a similar pattern is seen with the density (1.1 versus 1.6 g/mL for resin and 3.3 g/mL for glass particles). These features might explain why the mismatch problem seems to be more serious for embolic resin spheres [41][42][43]. The literature is controversial, however, since Kao et al [44], for instance, found excellent correspondence between 99m Tc-MAA SPECT and 90 Y PET dosimetry (median relative error 3.8 %).…”