SIRT and Its Unresolved Problems—Is Imaging the Solution? A Review

Abstract

Selective Internal Radiation Therapy (SIRT) is used as a treatment option for unresectable liver tumors. In SIRT, microspheres, which have a radioactive substance as an integral component, are placed via image guided catheters into the hepatic artery. The ionizing radiation is directly deli-vered to the tumor. Currently used commercially available microspheres are based on Yttrium 90, a β-emitter, which has been shown to be safe and to produce good clinical results. The technical features of Y90, their applications and their limitations are presented. Image guidance and intra-operative depiction of Yttrium 90 microspheres are restricted, which is currently one of the main limitations in SIRT. Therapy planning and control is currently based on pre-and post-operative images to evaluate the placement of the microspheres respectively. Holmium 166, another possi-ble nuclide integrated into the microspheres emits a higher amount of secondary γ-radiation (Bremsstrahlung) than Yttrium 90. This enables an improved depiction of the microspheres inside the patient during and immediately after application, but comes with other shortfalls. Imaging of delivery and verification of the microsphere placement could solve many of the identified prob-lems with SIRT. The different technologies are reviewed and an outlook in future developments is given particularly on image guidance and therapy control. Keywords Selective Internal Radiation Therapy (SIRT), Radioembolization, Yttrium 90, Holmium 166, Liver Tumors