## 2 Materials and Methods
### Patient Studies
#### 2.2.2 Patient Imaging  
SPECT-MAA and PET-MS imaging were always performed for clinical purposes, using a single AFOV of 406 mm and 180 mm long, respectively. These images were processed and analyzed following the same protocol for all treatments. All of the SPECT-MAA images were reconstructed with CTAC using the same clinical reconstruction parameters. In the initial nine treatments, we used the CT component of the PET/CT MS data acquisition. For the other seven treatments, we have acquired, on purpose, a CT data set (on our PET/CT system) immediately after the SPECT acquisition, as detailed below:  
1. Five multi-modality fiducial markers (Izi Medical) were fixed on the skin of the patient, one at the level of the xyphoid, one at the level of the inferior rib cage of the right, one at the level of the inferior rib cage on the left, one at the level of the spinous \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Pn\_t** & **Diagnosis** & \
\begin{tabular}{c} **No. Administrations** \\ **MAA MS** \\ \end{tabular} &
\begin{tabular}{c} **Administration Site** \\ **Total Volume (mL)** \\ \end{tabular} \\ \hline P1\_1 & Metastatic thymoma & 1 & 1 & proper hepatic artery & 16; 2-34; 241 \\ P2\_2 & Metastatic pancreatic cancer & 3 & 3 & (2) segment II \& III & 9; 4–79; 574 \\ P3\_3 & Metastatic colorectal cancer & 1 & 1 & proper hepatic artery & 3; 33–230; 314 \\ P4\_4 & Metastatic colorectal cancer & 2 & 2 & (2) segment II \& IV & 1; 462; 462 \\ P4\_5 & Metastatic colorectal cancer & 1 & 1 & right hepatic artery & 5; 7–508; 1626 \\ P5\_6 & Multifocal cholangiocarcinoma & 2 & 2 & (1) right hepatic artery & 6; 3–131; 451 \\ P6\_7 & Metastatic colorectal cancer & 2 & 2 & (2) left hepatic artery & 3; 27–300; 389 \\ P7\_8 & Metastatic colorectal cancer & 1 & 1 & proper hepatic artery & 5; 13–1016; 1154 \\ P8\_9 & Metastatic colorectal cancer & 1 & 1 & left hepatic artery & 8; 2–20; 123 \\ P8\_10 & Metastatic colorectal cancer & 1 & 1 & right hepatic artery & 5; 5–125; 202 \\ P9\_11 & Hepatocarcinoma & 1 & 1 & left hepatic artery & 1; 772; 772 \\ P10\_12 & Metastatic colorectal cancer & 1 & 1 & right hepatic artery & 14; 2–49; 93 \\ P11\_13 & cholangiocarcinoma & 1 & 1 & segment IV & 1; 256; 256 \\ P12\_14 & Hepatocarcinoma & 2 & 2 & (1) right hepatic artery & 1; 1047; 1047 \\ P13\_15 & Metastatic pancreatic cancer & 1 & 1 & right hepatic artery & 1; 510; 510 \\ P14\_16 & Cholangiocarcinoma & 2 & 2 & (1) right hepatic artery (I) & 2; 5–89; 94 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Eligible patients (n) and RE treatments (t) included in this work and PTV characterization. process of the second lumbar vertebra (L2), and finally, the other one at the level of the spinous process of the fourth lumbar vertebra (L4). These fiducial markers are small discs of CT radiopaque material that, when loaded with \({}^{99\text{m}}\)Tc, become visible during SPECT imaging [35]. Each fiducial marker was loaded with approximately 0.5 MBq of \({}^{99\text{m}}\)Tc, diluted in a physiological saline solution at a concentration of 50 MBq/0.5 mL immediately before the acquisition of the SPECT-MAA images. During the registration of the SPECT and CT images of the patients with fiducial markers attached to their skin, these were easily located on both SPECT and CT images and were used as reference points (i.e., landmarks) in the registration algorithm. 2. All these fiducial markers were used to assist in the registration of SPECT-MAA images with the corresponding CT images. The five fiducial markers were always applied on each of the last seven treatments. For the first nine treatments, for whom the fiducial markers technique was not used, the SPECT-MAA and CT images were registered by an experienced nuclear medicine physician, using the semi-automatic technique with cursor-based anatomical landmarks positioned in well-identified liver structural features of each patient's anatomy.