Clinical impact of 99mTc-MAA SPECT/CT-based dosimetry in the radioembolization of liver malignancies with 90Y-loaded microspheres

Abstract

Radioembolization with 90Y-loaded microspheres is increasingly used in the treatment of primary and secondary liver cancer. Technetium-99 m macroaggregated albumin (MAA) scintigraphy is used as a surrogate of microsphere distribution to assess lung or digestive shunting prior to therapy, based on tumoral targeting and dosimetry. To date, this has been the sole pre-therapeutic tool available for such evaluation. Several dosimetric approaches have been described using both glass and resin microspheres in hepatocellular carcinoma (HCC) and liver metastasis. Given that each product offers different specific activities and numbers of spheres injected, their radiobiological properties are believed to lightly differ. This paper summarizes and discusses the available studies focused on MAA-based dosimetry, particularly concentrating on potential confounding factors like clinical context, tumor size, cirrhosis, previous or concomitant therapy, and product used. In terms of the impact of tumoral dose in HCC, the results were concordant and a response relationship and tumoral threshold dose was clearly identified, especially in studies using glass microspheres. Tumoral dose has also been found to influence survival. The concept of treatment intensification has recently been introduced, yet despite several studies publishing interesting findings on the tumor dose-metastasis relationship, no consensus has been reached, and further clarification is thus required. Nor has the maximal tolerated dose to the liver been well documented, requiring more accurate evaluation. Lung dose was well described, despite recently identified factors influencing its evaluation, requiring further assessment. Conclusion: MAA SPECT/CT dosimetry is accurate in HCC and can now be used in order to achieve a fully customized approach, including treatment intensification. Yet further studies are warranted for the metastasis setting and evaluating the maximal tolerated liver dose.

Radioembolization Super Survivors: Extended Survival in Non-operative Hepatocellular Carcinoma

“…The application of segmental treatments significantly improved long-term OS in our cohort supporting the concept of radiation segmentectomy for improved preservation of liver parenchyma, especially in the absence of transplantation [11]. Dosing >200Gy was not associated with improved OS or earlier response consistent with the concept of threshold dose [11,18,19]. Y90 dosing has not been significantly linked to imaging response, survival, or toxicity [16,20,21].…”

High Impact of Preferential Flow on 99mTc-MAA and 90Y-Loaded Microsphere Uptake Correlation

“…Therefore, differences in the catheter position cannot be ruled out with certainty but seem quite unlikely and cannot be considered a major confounding issue. This is also supported by the results of Ulrich et al, who did not find any correlation between catheter position, 99m Tc-MAA uptake, and therapy response (6). Second, we experienced only a very limited number of vasospasms during angiography.…”

“…The lower correlation between 99m Tc-MAA and microsphere uptake in non-HCC liver tumors is supported by several studies, partly with high numbers of included patients. Ulrich et al found no significant correlation between response and 99m Tc-MAA uptake in 66 patients with colorectal liver metastases (6). Also, Wondergem et al reported significant differences in 99m Tc-MAA and microsphere uptake (7).…”

Biodistribution of 99mTc-MAA on SPECT/CT performed for 90Y-radioembolization therapy planning: a pictorial review

“…The main limitation to 90 Y radioembolization, however, is hepatopulmonary shunting of radiotracer and subsequent pulmonary injury. To avoid this complication, pre-procedural planning using 99m Tc-MAA is performed and lung shunt fractions are calculated, with 90 Y dosage adjusted accordingly or radioembolization avoided entirely [1]. …”