90Y-radioembolization is a palliative treatment for liver cancer. 90Y decays via beta emission, making imaging difficult due to absence of gamma radiation. Since post-procedure imaging is crucial, several theranostic radionuclides have been explored as alternatives. However, exposures to gamma radiation throughout the treatment caused concern for the organs near the liver. Geant4 Monte Carlo simulation using MIRD Pamphlet 5 reference phantom was carried out. A spherical tumour with 4.3cm radius was modelled within the liver. 1.82GBq of 90Y sources were isotropically distributed within the tumour, with no extrahepatic shunting. The simulation was repeated with 153Sm, 166Ho and 177Lu. The estimated tumour doses for all radionuclides were 262.9Gy. Tumour dose equivalent to 1.82GBq 90Y can be achieved with 8.32, 5.83, and 4.44GBq for 153Sm, 166Ho and 177Lu, respectively. Normal liver doses by the other radionuclides were lower than 90Y, hence beneficial for normal tissue sparing. The organ doses from 153Sm and 177Lu were relatively higher due to higher gamma energy, but were still well below 1Gy. 166Ho, 177Lu and 153Sm offer useful gamma emission for post-procedure imaging. They show potential as 90Y substitutes, delivering comparable tumour doses, lower normal liver doses and other organs doses far below the tolerance limit.