Theranostic Investigation of Gadolinium-159 for Hepatocellular Carcinoma: Monte Carlo Simulation Study

Gadolinium-159 (159Gd) is a beta emitter with appropriate energy for therapeutic application. However, this radioisotope additionally emits gamma rays, enabling the distribution of 159Gd to be detected by a gamma camera after each therapeutic administration. The current research is innovative in the investigation of 159Gd as a theranostic radioisotope in the radioembolization of HCC using Monte Carlo (MC) simulation. For 159Gd therapeutic investigation, various patient scenarios including varying tumour involvement (TI), tumour-to-normal liver uptake ratio (T/N), and lung shunting (LS) were simulated using Geant4 MC to estimate the absorbed doses to organs at risk. For 159Gd planar imaging investigation, the SPECTHead example from GATEContrib (GitHub) was utilized, and inside a liver a tumour was created and placed inside a torso phantom and simulated using GATE MC simulation. The majority of 159Gd absorbed doses by normal liver and lungs were less than the maximum dose limitations of 70 Gy and 30 Gy, respectively. Absorbed doses to other organs were observed to be below 1 Gy. The utilization of 58 keV and 363.54 keV photopeaks in combination produced optimal planar imaging of 159Gd. This research gives new insights into the use of 159Gd as a theranostic radioisotope, with the potential to be used as an Yttrium-90 (90Y) alternative for liver radioembolization.