## 3 Results and Discussion
### Absorbed Dose to Other Organs  
In order to estimate the absorbed dose from \({}^{159}\)Gd to other organs when 120 Gy is delivered to the tumour, we selected the parameter combinations which have higher impacts on the absorbed dose: TI (70%), LS (20%), and T/N (1), as illustrated in Figure 9.  
The outcome following radioembolization is predominantly linked to the radiation dose absorbed by normal liver, lungs, and other organs [30]. As radiation oncologists carry out hepatic brachytherapy on a routine basis, they should have an empirical comprehension of the absorbed dose which reaches the tumour [31]. This is paramount in order to maximize the radiation received by the tumour and to reduce the collateral damage to normal tissue as much as possible. Previously, hepatic radioembolization has been applied without a precise appreciation of the respective quantities of radiation absorbed by the normal liver, lungs, and other organs [32; 33]. From this study, it has been observed that the absorbed dose to the normal liver is primarily dependent on T/N because when T/N increases, the absorbed doses of the normal liver decrease due to the lower administered activity required to deliver the 120 Gy tumour dose [34] and not due to TI and LS (Figure 6). The absorbed dose to left and right lungs are impacted by all three factors, i.e., TI, LS, and T/N; and LS was the most influential parameter [35] as illustrated in Figures 7 and 8. Figure 9 show the absorbed doses from gamma emission to the other organs which are similar in shape and equal in mass; it is clearly observed that organs located on the same side as the liver (right side of the body) absorb a higher dose than organs located on the left side according to the inverse square law, and the absorbed dose to other organs decreases as the distance from the liver increases [36]. The highest absorbed dose was found in the right adrenal because it is located just below the liver. Despite the fact that the right and left adrenals are roughly equal in mass, the right adrenal absorbs a significantly higher dose than the left adrenal due to their unequal distance from the liver, as shown in Figure 9. Results demonstrate that \({}^{159}\)Gd gamma emission is not risky and is completely safe, and that the treatment is not restricted by the absorbed dose received by other organs. This is because when 120 Gy is delivered to the tumour, all other organs' absorbed doses were below 1 Gy or only less than 1% as compared to the absorbed dose given to the tumour. This was supported by  
Figure 9: Absorbed dose to other organs for tumour involvement of 70%, lung shunting (LS) (20%), and tumour to normal liver uptake ratio (T/N) 1, when 120 Gy is delivered to the tumour. L: left, R: right, ULI: upper large intestines, LLI: lower large intestines. dosimetric research for radioembolization with Holmium-166 microspheres, which found that the gamma emission contributed just 1.1% of the overall absorbed dose [37]. The \({}^{90}\)Y, \({}^{166}\)Ho, \({}^{153}\)Sm, and \({}^{177}\)Lu radioisotopes have been studied and investigated by [PERSON] et al. (2016) using the MIRD phantom. However, in their study it was concluded that the total estimated tumour dose for all radionuclides was 262.9 Gy. Furthermore, the tumour dose of 1.82 GBq \({}^{90}\)Y has been obtained, whereby \({}^{153}\)Sm, \({}^{166}\)Ho, and \({}^{177}\)Lu obtained same tumour doses at 8.32, 5.83, and 4.44 GBq, respectively. In terms of comparison, the normal liver doses of the other radionuclides were lower than \({}^{90}\)Y, which was advantageous for sparing normal tissue. Interestingly, even though the other organ doses from \({}^{153}\)Sm and \({}^{177}\)Lu were higher due to higher gamma energy, they were still below 1 Gy. They show promise as \({}^{90}\)Y substitutes, delivering comparable tumour doses, reduced normal liver and lung doses, and doses absorbed by other organs considerably below the tolerance limit [13].