Open XAML Window in Visual Studio Extension and Lock DTE Until window is closed again

I got a Visual Studio Extension project. 

In this Project I got a XAML window. 
In a ContextMenu click, I'm open the window up. 

Like this:

var window = new XamlWindow();
window.Show();

When I do this I want to lock the DTE until you have closed the window again. 
Just as the "Add New Item" window works. You cant do anything els until you have closed the window again. 

I have tried to find settings for this on the window, but cant find anything about it.
How can I acomplish this?