SIRT of liver metastases: physiological and pathophysiological considerations

• Published in: European journal of nuclear medicine and molecular imaging 2012-10, Vol.39 (10), p.1646-1655
• Main Authors: Van de Wiele, Christophe, Maes, Alex, Brugman, Eddy, D’Asseler, Yves, De Spiegeleer, Bart, Mees, Gilles, Stellamans, Karin
• Format: Article
• Language: English
• Subjects: Albumin; Angiotensin II; Animals; Cardiology; Data processing; Humans; Imaging; Liver; Liver cancer; Liver Circulation - radiation effects; Liver Neoplasms - blood supply; Liver Neoplasms - radiotherapy; Liver Neoplasms - secondary; Medicine; Medicine & Public Health; Metastases; Metastasis; Microspheres; Microvasculature; Nuclear Medicine; Oncology; Orthopedics; Pathology; Radiation; Radiation therapy; Radiology; Review Article; Reviews; Rheology; Scintigraphy; Starch; Yttrium Radioisotopes - therapeutic use
• ISSN: 1619-7070; 1619-7089
• DOI: 10.1007/s00259-012-2189-6

Available literature on the differences in circulation and microcirculation of normal liver and liver metastases as well as in rheology of the different radiolabelled microspheres [ 99m Tc-labelled macroaggregates of albumin (MAA), 90 Y-TheraSpheres and 90 Y-SIR-spheres] used in selective internal radiation therapy (SIRT) are reviewed and implications thereof on the practice of SIRT discussed. As a result of axial accumulation and skimming, large microspheres are preferentially deposited in regions of high flow, whereas smaller microspheres are preferentially diverted to regions of low flow. As flow to normal liver tissue is considerably variable between segments and also within one segment, microspheres will be delivered heterogeneously within the microvasculature of normal liver tissue. This non-uniformity in microsphere distribution in normal liver tissue has a significant “liver-sparing” effect on the dose distribution of 90 Y-labelled microspheres. Arterial flow to liver metastases is most pronounced in the hypervascular rim of metastases, followed by the smaller metastases and finally by the central hypoperfused region of the larger metastases. Because of the wide variability in size of labelled MAAs and because of the skimming effect, existing differences in flow between metastatic lesions of variable size are likely exaggerated on 99m Tc-MAA scintigraphy when compared to 90 Y-TheraSpheres and 90 Y-SIR-spheres (smaller variability in size and probably also in specific activity). Ideally, labelled MAAs would contain a size range similar to that of 90 Y-SIR-spheres or 90 Y-TheraSpheres. Furthermore, the optimal number of MAA particles to inject for the pretreatment planning scintigraphy warrants further exploration as it was shown that concentrated suspensions of microspheres produce more optimal tumour to normal liver distribution ratios. Finally, available data suggest that the flow-based heterogeneous distribution of microspheres to metastatic lesions of variable size might be optimized, that is rendered more homogeneous, through the combined use of angiotensin II and degradable starch microspheres.