The PTR keyword denotes an integral type that stores a pointer to a memory location. It is usually compiled to the System.IntPtr .Net Type.
Please note that the size of the PTR depends on the underlying operating system and it will also be different when your application runs in x86 or x64 mode.
In Visual Objects PTR is always 32 bits. Many people have written code that CAST INT values to PTR and back. This works because both values are 32 bit in VO.
Safe code in .Net cannot do this, since the size of PTR is not fixed.