## 3 Results
### MR Findings  
#### 3.3.1 MR Findings with Respect to Irradiated Tumors  
The MR findings with respect to irradiated tumors are summarized in Table 3.  
After MR imaging, _radiation induced necrosis_ was appreciable in 4/9 patients. Radiation-induced necrosis showed high signal intensity on T1-weighted, low signal intensity on T2-weighted, no restriction on DW images, and no enhancement on contrast-enhanced fat-suppressed T1-weighted images (Figure 1). In the one remaining patient with histopathologic evidence of necrosis (Table 3), the irradiated tumor was characterized by microscopic foci of necrosis, only appreciable under pathologic examination and, therefore, below the resolving power (spatial resolution) of MR imaging. At MR imaging _fibrosis_ was appreciable in 1/9 patients. Fibrosis showed intermediate signal intensity on T1-weighted images, low signal intensity on T2-weighted images, no restriction on DW images, and moderate enhancement on contrast-enhanced fat-suppressed T1-weighted images. At MR imaging _viable tumor tissue_ was appreciable in 7/9 patients. The MR appearance of viable tumor tissue resembled that of primary melanoma, largely depending on the melanin content. Typical pigmented melanomas showed high signal intensity on T1-weighted images and low signal intensity on T2-weighted images. Poorly pigmented lesions demonstrated intermediate signal intensity on both T1- and T2-weighted sequences. In any case, viable tumor tissue displayed restricted diffusion on DW sequences (high signal intensity on DW images, low signal intensity on the ADC map) due to high cellularity. Table 5 summarizes the MR imaging appearance of irradiated uveal melanomas. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Patient**} & **Radiation-Related** & **Vitreous** & **Optic Nerve** & **Iris Neovascular-** & **Periocular** \\  & **Intracocular Inflammation** & **Hemorrhage** & **Degeneration** & **ization** & **Fibrotic Adhesion** \\ \hline
1 & - & Yes & - & - & - \\
2 & Yes & - & - & - & - \\
3 & - & - & Yes & - & - \\
4 & - & - & - & - & - \\
5 & Yes & - & Yes & - & - \\
6 & Yes & - & - & Yes & - \\
7 & - & - & Yes & - & Yes \\
8 & - & Yes & - & - & - \\
9 & - & - & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Histopathologic findings with respect to irradiated extratumoral ocular tissues. Figure 1: _Radiation-induced necrosis._ A 60-year-old male patient (patient n. 3 of our series) affected by choroidal melanoma of the right eye treated with proton beam radiotherapy. Secondary enucleation was performed 35 months after radiotherapy because of local recurrence. Axial (**a**) T2-weighted turbo spin-echo STIR, (**b**) fat-suppressed T1-weighted, (**c**) DW (b = 1000 s/mm\({}^{2}\)), and (**d**) contrast-enhanced fat-suppressed T1-weighted images. A dome-shaped mass along the posterior aspect of the globe, covering the optic disc, shows central and lateral portions (white arrows) with intermediate signal intensity on the T2-weighted image and moderately high signal intensity on the T1-weighted image, indicative of viable tumor; the medial portion of the lesion (white arrowhead) exhibits low signal intensity on the T2-weighted image and high signal intensity on the T1-weighted image—a finding consistent with radiation-induced necrosis characterized by dispersion of the melanin pigment. The sharp boundary that separates the two different components of the lesion is better visible on the T2-weighted image. The viable tumor (white arrow) shows restricted diffusion with high signal intensity due to high cellularity on the DW image, and mild enhancement on the contrast-enhanced fat-suppressed T1-weighted image; the medial necrotic part (white arrowhead) displays no restriction on DW image and lack of contrast enhancement on T1-weighted image. Note a retinal detachment (white asterisks), lateral to the mass, with intermediate signal intensity on the T2- and T1-weighted images, and without contrast enhancement.