Holmium radioembolization : Efficacy and safety

Abstract

This thesis describes the application of holmium-166 (166Ho) microspheres for radioembolization of hepatic malignancies. In radioembolization, a scout dose of technetium-99m macroaggregated albumin (99mTc-MAA) is injected in the hepatic artery first, as a scout dose, to screen for any of two contraindications for treatment: deposition of microspheres in the lungs (by shunting into the hepatic vein) or in extrahepatic tissue (by incorrect targeting of the liver). However, we found that a scout dose of 99mTc-MAA does not accurately predict the lung shunt. Also, if another modality is used to image the scout dose, the lung shunt differs; planar scintigraphy overestimated the lung shunt of 99mTc-MAA compared with SPECT/CT. The second contraindication, extrahepatic deposition, can occur in, for example, the gallbladder. We showed that the absorbed dose to the gallbladder can by decreased by a small catheter adjustment which alters the preferential blood flow. Although 99mTc-MAA is commonly used to check for extrahepatic depositions, a scout dose can also consist of 166Ho microspheres. The advantage would be that the same microspheres are used for a scout dose and for treatment, which could increase the predictability of the treatment dose. Better treatment planning could increase efficacy and reduce toxicity. The disadvantage is that 166Ho microspheres emit beta radiation and could cause the same adverse events which a scout dose should prevent. However, we found that the radiation dose of a scout dose of 166Ho microspheres is not high enough to cause adverse events in the majority of patients. If the scout dose indicates that treatment is safe, patients can be treated with 166Ho microspheres. We found that treatment showed efficacy and is safe in salvage patients with liver metastases: in 49% of all patients, tumors in the liver did not show progression for 3 months after treatment. Furthermore, most of the adverse events were transient and were related to the so-called post radioembolization syndrome which consists of abdominal pain, nausea, vomiting, fever and fatigue. After treatment, patient emits radiation for which contact restrictions should be given, but we found these are necessary in only a minority of patients.