## 3 Results
### Tumor Object Characteristics  
Table 2 summarizes tumor object characteristics and reports the target registration error. Descriptive analysis of the segmented tumor volumes revealed a mean tumor volume of \(13.6\pm 16.0\) cm\({}^{3}\) (mean \(\pm\) SD) and a median of \(8.5\) cm\({}^{3}\) in MRI, whereas it was \(13.5\pm 16.0\) cm\({}^{3}\) (mean \(\pm\) SD) with a median of \(8.8\) cm\({}^{3}\), when segmented in ultrasound. The data were not normally distributed (D'Agostino and Pearson test). For further analysis a two-tailed Wilcoxon matched pairs test was used (Figure 2), demonstrating a median of differences of \(0.11\) cm\({}^{3}\), which was not significant (\(p=0.0595\)). To take into account that some of the values were negative and thus the median of differences might be misleading, we also determined the median of the magnitude of the differences, which was \(0.40\) cm\({}^{3}\) \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Case**} & **Age** & \multirow{2}{*}{**Sex**} & \multirow{2}{*}{**Localization**} & **Diagnosis/** \\  & **[Years]** & & & **Primary Tumor** \\ \hline
1 & 59.5 & male & left frontal & melanoma \\
2 & 73.3 & male & right frontal & ADC, colon \\
3 & 32.7 & male & left frontal & melanoma \\
4 & 64.2 & male & cerebellar & ADC, lung \\
5 & 50.7 & female & left temporal & ADC, lung \\
6 & 69.0 & male & right parietio-occipital & ADC, gall bladder \\
7 & 78.1 & male & cerebellar & RCC \\
8 & 76.6 & female & left occipital & ADC, lung \\
9 & 79.1 & male & right frontal & RCC \\
10 & 62.8 & female & left frontal & ADC, lung \\
11 & 57.2 & female & left frontal & CA, CUP \\
12 & 59.2 & female & cerebellar & ADC, lung \\
13 & 62.8 & female & left frontal & NEC, lung \\
14 & 56.7 & female & left frontal & melanoma \\
15 & 67.3 & female & left parietal & RCC \\
16 & 72.8 & male & right insular & ADC, GI \\
17 & 74.1 & female & left occipital & ADC, colon \\
18 & 71.1 & male & cerebellar & RCC \\
19 & 56.0 & male & left frontal & melanoma \\
20 & 28.6 & female & right frontal & mammary CA (NST) \\
21 * & 53.5 & male & right frontal & NEC, lung \\
22 & 50.5 & female & right occipital & melanoma \\
23 & 59.5 & male & left parietal & ADC, lung \\
24 & 51.2 & female & cerebellar & NEC, lung \\
25 & 65.3 & female & left temporo-parietal & ADC, lung \\
26 & 74.6 & female & left occipital & ADC, colon \\
27 & 71.5 & male & left frontal & ADC, esophagus \\
28 & 78.2 & male & left temporal & melanoma \\
29 & 67.6 & female & left parietal & NEC, lung \\
30 & 69.5 & female & cerebellar & ADC, lung \\
31 & 55.4 & female & right frontal & ADC, lung \\
32 & 70.7 & male & right frontal & ADC, lung \\
33 & 41.8 & female & right frontal & mammary ADC \\
34 & 69.7 & male & right parietal & mammary ADC \\
35 & 58.6 & male & left CN & melanoma \\
36 & 58.6 & male & left frontal & ADC, lung \\
37 * & 64.9 & female & left frontal & ADC, lung \\ \hline \hline \end{tabular} ADC: adenocarcinoma; CA: carcinoma; CN: caudate nucleus; CUP: carcinoma of unknown primary site; GI: gastrointestinal; NEC: neuroendocrine carcinoma; NST: no specific type; RCC: renal cell carcinoma; *patient excluded.  
\end{table} 
Table 1: Patient characteristics. The mean Dice coefficient C\({}_{\text{DSC}}\) was \(0.68\pm 0.22\) (mean \(\pm\) SD) with a median of 0.75. As demonstrated in Figure 3, the Dice coefficient ranged from 0 (case no. 31) to 0.88 (case no. 11). When looking at the cases with a Dice coefficient below 0.5, it is noteworthy that the median tumor size (segmented in MRI) was significantly (\(p\) = 0.0001, two-tailed Mann-Whitney test) smaller in this subgroup (0.7 cm\({}^{3}\) vs. 9.8 cm\({}^{3}\)). MRI-segmented tumor volume and Dice coefficient correlated positively (r = 0.59, \(p\) = 0.0002, nonparametric Spearman correlation).